Iridium(III) in Optoelectronic and Photonics Applications

The fundamental photophysical properties of iridium(III) materials make this class of materials the pre-eminent transition metal complex for use in optoelectronic applications.

Iridium(III) in Optoelectronic and Photonics Applications represents the definitive account of photoactive iridium complexes and their use across a wide variety of applications.  This two-volume set begins with an overview of the synthesis of these complexes and discusses their photophysical properties. The text highlights not only mononuclear complexes but also the properties of multinuclear and polymeric iridium-based materials and the assembly of iridium complexes into larger supramolecular architectures such as MOFs and soft materials. Chapters devoted to the use of these iridium-based materials in diverse optoelectronic applications follow, including: electroluminescent devices such as organic light emitting diodes (OLEDs) and light-emitting electrochemical cells (LEECs); electrochemiluminescence (ECL); bioimaging; sensing; light harvesting in the context of solar cell applications; in photoredox catalysis and as components for solar fuels.

Although primarily targeting a chemistry audience, the wide applicability of these compounds transcends traditional disciplines, making this text also of use to physicists, materials scientists or biologists who have interests in these areas.

• Language: English
• Publisher: Wiley
• Release date: Mar 7, 2017
• ISBN: 9781119007159

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Table of Contents

Cover

Volume 1

Title Page

List of Contributors

Foreword

Preface

1 Archetypal Iridium(III) Compounds for Optoelectronic and Photonic Applications: Photophysical Properties and Synthetic Methods

1.1 Introduction

1.2 Iridium Complex Ion Dopants in Silver Halide Photographic Materials

1.3 Overview of the Photophysical Properties of C^N and C^C: Cyclometalated Ir(III) Complexes

1.4 Importance of Ir─C Bonds in the Archetypal Ir(III) Complexes for Optoelectronic and Photonic Applications

1.5 Tuning Emission Color

1.6 Absorbance and Photoluminescence of C^N Cyclometalated Ir(III) Complexes

1.7 SOC Mechanism: Radiative Decay Rates and ZFS

1.8 Non‐Radiative Decay Rates

1.9 Synthetic Methods Targeting C^N Cyclometalated Ir(III) Compounds

1.10 Synthetic Methods for Cyclometalated Ir(III) Compounds Containing Carbenes

1.11 Conclusions

Acknowledgements

Abbreviations for Ligands in Ir(III) Complexes

References

2 Multinuclear Iridium Complexes

2.1 Introduction

2.2 Compounds Incorporating ‘Single Atom Bridges’: μ‐Chloro, μ‐Oxo and μ‐Aza

2.3 Polyatomic Acyclic Bridges: Acetylides, Cyanides and Hydrazides

2.4 Compounds with Heterocyclic Bridges

2.5 Multinuclear Complexes Featuring Conjugated Bridges between Iridium‐Bound Polypyridyl or Arylpyridyl Ligands

2.6 Concluding Remarks

Acknowledgements

References

3 Soft Materials and Soft Salts Based on Iridium Complexes

3.1 Introduction

3.2 Liquid Crystals

3.3 Gels

3.4 Micelles

3.5 Langmuir–Blodgett Films

3.6 Soft Salts

3.7 Conclusion

Acknowledgements

References

4 Porous Materials Based on Precious Metal Building Blocks for Solar Energy Applications

4.1 Introduction

4.2 The Luminescent Nature of MOFs and Their Use in Chemical Applications

4.3 Energy Transfer in Porous Materials

4.4 Porous Materials for Water Oxidation

4.5 Porous Materials for Proton Reduction

4.6 Porous Materials for CO2 Reduction

4.7 Conclusions and Outlook

References

5 Polymeric Architectures Containing Phosphorescent Iridium(III) Complexes

5.1 Introduction

5.2 Ir(III)‐Containing Polymers: Classification, Design Principles, and Syntheses

5.3 Hyperbranched and Dendritic Architectures

5.4 Concluding Remarks

References

6 Iridium(III) Complexes for OLED Application

6.1 Introduction

6.2 Iridium Complexes

6.3 Organic Light‐Emitting Diodes

6.4 Iridium(III) Complexes for PHOLED Application

6.5 Conclusions and Perspectives

References

7 A Comprehensive Review of Luminescent Iridium Complexes Used in Light‐Emitting Electrochemical Cells (LEECs)

7.1 Introduction

7.2 Device Fundamentals

7.3 Green Emitters

7.4 Blue Emitters

7.5 Yellow Emitters

7.6 Orange‐Red Emitters

7.7 Conclusions and Outlook

Acknowledgements

References

Volume 2

Title Page

List of Contributors

Foreword

Preface

8 Electrochemiluminescence of Iridium Complexes

8.1 Background and Overview of Electrochemiluminescence

8.2 Iridium ECL

List of Ligand Abbreviations Used in Text

References

9 Strategic Applications of Luminescent Iridium(III) Complexes as Biomolecular Probes, Cellular Imaging Reagents, and Photodynamic Therapeutics

9.1 Introduction

9.2 General Cellular Staining Reagents

9.3 Hypoxia Sensing Probes

9.4 Molecular and Ion Intracellular Probes

9.5 Organelle‐Targeting Bioimaging Reagents

9.6 Functionalized Polypeptides for Bioimaging

9.7 Polymers and Nanoparticles for Bioimaging

9.8 Photocytotoxic Reagents and Photodynamic Therapeutics

9.9 Conclusion

Acknowledgements

Abbreviations

References

10 Iridium Complexes in the Development of Optical Sensors

10.1 Generalities of Optical Sensors

10.2 Ir(III) Used as Optical Probes

10.3 Ir(III) Used in the Development of Sensing Phases

10.4 Conclusion and Future Challenges

Acronyms Used in the Names of the Complexes

References

11 Photoredox Catalysis of Iridium(III)‐Based Photosensitizers

11.1 Introduction

11.2 Iridium‐Based Photoredox Catalysis in Organic Synthesis

11.3 Conclusion

References

12 Solar Fuel Generation

12.1 Introduction

12.2 Fundamentals of [Ir(C^N)2(N^N)] Photosensitizers

12.3 Application of [Ir(C^N)2(N^N)] in Photocatalytic Water Reduction

12.4 Alternative Iridium Structures

12.5 Outlook

Acknowledgements

References

13 Iridium Complexes in Water Oxidation Catalysis

13.1 Introduction

13.2 Sacrificial Oxidants

13.3 Molecular Iridium Catalyst for Water Oxidation

13.4 Conclusions

Acknowledgements

Glossary of Terms and Abbreviations

References

14 Iridium Complexes as Photoactive Center for Light Harvesting and Solar Cell Applications

14.1 Introduction

14.2 Photoinduced Electron Transfer in Multicomponent Arrays

14.3 Iridium Complexes as Photoactive Center for Solar Cell Applications

14.4 Conclusions

References

Index

End User License Agreement

List of Tables

Chapter 02

Table 2.1 Photophysical properties of selected multinuclear iridium complexes with single atom or acyclic bridges, discussed in Sections 2.2 and 2.3.

Table 2.2 Photophysical properties of selected multinuclear iridium complexes with heterocyclic bridges, discussed in Section 2.4.

Chapter 06

Table 6.1 Commercial OLEDs efficiency and lifetime.

Table 6.2 Summary of the main photophysical data and device characteristics. All the abbreviation used can be found in Table 6.3.

Table 6.3 Abbreviation list.

Chapter 07

Table 7.1 Summary of LEECs reported employing green‐emitting complexes, where ‘green’ has been nominally defined as solution‐state emission maxima in the range of 501–560 nm. Complex 46 is included here due to pertinence to discussion.

Table 7.2 Summary of LEECs reported employing blue‐/blue‐green‐emitting complexes defined as λPL < 500 nm.

Table 7.3 Summary of LEECs reported employing yellow‐/yellow‐orange‐emitting complexes, nominally defined as solution‐state emission maxima in the range of 561–599 nm.

Table 7.4 Summary of LEECs reported employing orange‐red‐/red‐emitting complexes, nominally defined as solution‐state emission maxima with λPL > 599 nm.

Chapter 08

Table 8.1 Electrochemical, photophysical and ECL data for Ir(ppy)3, Ir(dfppy)3 and the complexes in Figure 8.35.

Chapter 10

Table 10.1 Ir(III) complexes used as optical probes for detecting O2.

Table 10.2 Ir(III) complexes used as optical probes for detecting CO2, CO, and VOCs.

Table 10.3 Ir(III) complexes used as optical probes for detecting cations.

Table 10.4 Ir(III) complexes used as optical probes for detecting pH.

Table 10.5 Ir(III) complexes used as optical probes for detecting anions.

Table 10.6 Ir(III) complexes used as optical probes for detecting biomolecules.

Table 10.7 Ir(III) complexes used as optical probes for detecting other small molecules.

Table 10.8 Optical sensing layers based on Ir(III) complexes for analyzing oxygen.

Table 10.9 Optical sensing layers based on Ir(III) complexes for analyzing ions.

Table 10.10 Optical sensing layers based on Ir(III) complexes for analyzing biomolecules.

Table 10.11 Optical sensing layers based on Ir(III) complexes for multiparametric sensing.

Chapter 12

Table 12.1 Summary of selected iridium‐based photosensitizers used for photocatalytic water reduction.

Chapter 13

Table 13.1 Summary of experimental parameters of CAN.

Table 13.2 Summary of catalytic results for iridium WOCs without Cp*.

Table 13.3 Summary of catalytic results for Cp*Ir WOCs.

Table 13.4 Summary of catalytic results for Cp*Ir WOCs bearing normal carbene ligands.

Table 13.5 Summary of catalytic results for Cp*Ir WOCs bearing abnormal carbene ligands.

Table 13.6 Summary of catalytic results for Cp*Ir WOCs bearing mesoionic imidazolylidene or mesoionic triazolylidene ligands.

Table 13.7 Summary of catalytic results for Cp*Ir WOCs incorporated into supports and homogeneous analogue.

Table 13.8 Photocatalytic performance of heterogeneous and homogeneous iridium WOC with [Ru(bpy)3]²+ and Na2S2O8.

List of Illustrations

Chapter 01

Scheme 1.1 Sterochemical diagrams of representative archetypal Ir(III) cyclometalates.

Scheme 1.2 Structural formulae of additional examples of Ir(III) cyclometalates.

Scheme 1.3 Structural formulae of representative Ir(III) cyclometalates comprising carbene ligands.

Scheme 1.4 Sterochemical diagrams of representative Ir(III) cyclometalates comprising tridentate ligands.

Figure 1.1 Energy level diagram for one‐electron orbitals in d⁶ MLCT–LC complexes.

Figure 1.2 Jablonski diagram for the many‐electron states in d⁶ MLCT–LC complexes.

Figure 1.3 Absorption, excitation, and emission spectra of Ir(ppy)3 in CH2Cl2 at 300 and 77 K as indicated.

Figure 1.4 Absorption and emission spectra of Ir(btp)2(acac) in CH2Cl2 at 300 K. Dashed line shows absorption on a scale expanded by a factor of 100.

Figure 1.5 Absorption and emission spectra of Ir(ppy)2(CO)(Cl) in THF at 300 K (solid curves). Dashed curve is the absorption spectrum of Ir(ppy)3 for comparison.

Figure 1.6 Emission spectra for several members of the series Ir(tpy)2(LX) (tpy = 2‐(p‐tolyl)pyridine) at room temperature (a) and 77 K (b) in 2‐MeTHF.

Figure 1.7 Emission spectra for the series mer‐Ir(piq)3−x(ppy)x (x = 0–2) and fac‐Ir(piq)3 at room temperature (top) in PMMA.

Figure 1.8 Temperature dependence of emission decay of Ir(ppy)3 in THF (λex = 337 nm). Inset on the left is on an enlarged scale for the lowest temperatures. Inset on the right lists the ZFS and sublevel decay times obtained from a fit to Equation 1.11 (solid line).

Figure 1.9 Correlation of average emission decay time at room temperature determined as described in the text with the ZFS for a variety of d⁶ and d⁸ MLCT–LC emitters. Open symbols represent radiative decay times. Shaded bar across the bottom indicates the classification of the emitting triplet sates as dominantly LC–LC with intermediate admixture of MLCT character or strongly MLCT in character.

Figure 1.10 Correlation diagram of metal dπ and ligand π orbitals according to the single‐ligand‐localized model in C2v symmetry in the coordinate system shown.

Figure 1.11 Plots of krversus (ΔE)−2 [ν(T1)/ν(¹MLCT)]³ (a) and ε for the lowest energy absorption versus (ΔE)−2 [ν(T1)/{ν(¹MLCT)}³] and (b) for the series Ir(tpy)2(LX).

Figure 1.12 (a) and (b) Emission spectra of Ir(ppy)3 in THF at various temperatures (λex = 364 nm).

Figure 1.13 Magnetic field effect upon emission spectrum of Ir(ppy)3 in THF at 1.5 K (λex = 458 nm). Inset illustrates diagrammatically the magnetic field‐induced borrowing of level II intensity allowed by SOC.

Figure 1.14 Energy level schematic of the three triplet sublevels of Ir(ppy)3 in THF and their allowed transitions to the ground state. Dashed lines labeled FC and HT represent Franck–Condon and Herzberg–Teller (odd‐parity) active vibrational modes, respectively. ZFS and decay times determined from the fit to Equation 1.11 shown in Figure 1.8 are also included.

Figure 1.15 Emission spectra of FIrpic in CH2Cl2 Shpol’skii matrix and in THF at 4.2 K from nonselective excitation at 355 nm.

Figure 1.16 High resolution, site‐selective (a) excitation (νem = 21,738 cm−1) and (b) emission (νex = 21,814 cm−1) spectra of FIrpic in CH2Cl2 Shpol’skii matrix at 4.2 K.

Figure 1.17 Emission spectrum of FIrpic in CH2Cl2 Shpol’skii matrix at 1.5 K following site‐selective excitation into the electronic origin of sublevel III of site A at 21,814 cm−1. The energy difference between the vibrational satellites and the electronic origin of sublevel I at 21,738 cm−1 are indicated about the satellite peaks.

Figure 1.18 Temperature dependence of emission lifetime for two blue‐emitting complexes that exhibit thermally activated non‐radiative decay above 250°C. Solid lines are fit to Equation 1.16.

Chapter 02

Figure 2.1 Chloro‐bridged dimers, exemplified by [Ir(N^C‐ppy)2(μ‐Cl)]21, are versatile intermediates in the synthesis of several of the main classes of photoactive, mononuclear Ir complexes.

Figure 2.2 Diagrammatic representation of the meso and racemic forms of [Ir(ppy)2(μ‐Cl)]21, and the crystal structure of [Ir(Meppy)2(μ‐Cl)]22 showing that the racemic form is the one obtained in practice (the structure of the ΛΛ enantiomer is shown [8]).

Figure 2.3 The formation of bis‐μ‐isocyanate‐bridged iridium complexes from chloro‐bridged dimers.

Figure 2.4 The reaction of chloro‐bridged dimers 1 and 2 with 3,5‐diphenylpyrazole (Ph2pzH) or 3‐phenyl‐5‐methylpyrazole (PhMepzH) in the presence of NaOMe as a base; adventitious water leads to the bridging OH groups in 5, 6, 7 and 9.

Figure 2.5 Cyclic voltammogram of 5 in CH2Cl2 at a scan rate of 100 mV s−1 (solid line) and differential pulse voltammogram with a step potential of 5 mV and an amplitude of 50 mV (broken line).

Figure 2.6 Structures of acetylide‐bridged di‐iridium compounds prepared by Lalinde and co‐workers.

Figure 2.7 Molecular structures of (a) 10a and (b) 10d in crystals grown by slow diffusion of n‐hexane into acetone solutions, obtained by X‐ray diffraction. Two molecules of acetone were found per molecule of Ir2 in each structure (not shown).

Figure 2.8 The proposed dynamic equilibria in the acetylide‐bridged Ir dimers, involving (i) fast inversion of the central bent Ir2(C≡C) dimetallacycle and (ii) fast σ/π intramolecular exchange of both C≡CR groups within the dimetallacycle.

Figure 2.9 Structural formula (bottom) and molecular structure in the crystal (top left) of the tetranuclear Ir complex 11 (hydrogen atoms are omitted from the structure for clarity). The representation in the top right omits selected phenyl rings to make clear the presence of two types of iridium centre in the structure, as well as the intramolecular π–π* interaction.

Figure 2.10 Top: X‐ray molecular structures of 12a (left) and 12b (right), with hydrogen atoms omitted for clarity. Bottom: the core parts of the respective structures; note the internal mirror plane in the ΛΔ structure of 12a.

Figure 2.11 Representative N^N‐coordinating bridging ligands. All those shown are charge neutral except for bpt−, the anion of bis(2‐pyridyl)‐1,2,4‐triazole.

Figure 2.12 Structures of 13 and 14 incorporating dpp, and of 15, 16, 17 and 18 incorporating HAT, bpt, tpphz and dpbq, respectively.

Figure 2.13 Molecular structures of (a) 19 (charge 2+), (b) 20 (3+) and (c) 21 (1+) in the crystals. Anions are not shown, and hydrogen atoms are omitted from 20 and 21 for clarity.

Figure 2.14 Diagrammatic structures of the three stereoisomers of 22 and of the TRISPHAT anion (Δ enantiomer).

Figure 2.15 ¹H NMR spectra (400 MHz, CDCl3/CD3CN 85/15) of (a) isomeric mixture of 22[Δ‐TRISPHAT]2 salts as synthesised, (b) the first eluted complex ΔΔ‐22[Δ‐TRISPHAT]2, (c) the second eluted complex meso‐(ΔΛ)‐22[Δ‐TRISPHAT]2 and (d) the last eluted complex ΛΛ‐22[Δ‐TRISPHAT]2, in lower diastereoisomeric purity.

Figure 2.16 Circular dichroism spectra of (a) ΔΔ‐22[Δ‐TRISPHAT]2, (b) meso‐(ΔΛ)‐22[Δ‐TRISPHAT]2 and (c) ΛΛ‐22[Δ‐TRISPHAT]2 in CH2Cl2 at 298 K. (Note that the Δ‐TRISPHAT anion common to all three is CD‐active at wavelengths <300 nm.)

Figure 2.17 Selected N^C‐coordinating bridging ligands discussed in this section. The protons that are lost in the process of bis‐cyclometallation are explicitly shown.

Figure 2.18 Structures of multinuclear complexes 23 and 24, incorporating bis‐N^C‐coordinating bridging ligands, and of the bis-: C^C− N‐heterocyclic carbene‐bridged Ir2 compound 26.

Figure 2.19 Absorption (top) and emission (bottom) spectra of complexes incorporating 4,6‐di‐(4‐tert‐butylphenyl)pyrimidine in CH2Cl2 at 298 K. Key: Pt and Ir are the respective mononuclear complexes Pt(N^C‐dppymH)(acac) and Ir(N^C‐dppymH)2(acac), Pt2 is [(dppym)Pt2(acac)2] and Pt2Ir is the heterotrinuclear compound 24.

Figure 2.20 Synthesis of Ir2(dpyp‐pym)(Meppy)2Cl225; schematic illustration of the relative disposition of the Cl ligands (centre) and corresponding structures obtained by X‐ray diffraction (right; for clarity, the structures are shown without H atoms, solvent molecules and minor disorder components) [35].

Figure 2.21 Structural formulae of selected multinuclear complexes incorporating C≡C and N═N linkages between the bipyridine ligands.

Figure 2.22 Structural formulae of selected multinuclear complexes incorporating phenyl rings within the bridges.

Figure 2.23 Synthetic route to multimetallic tetranuclear complex 34, employing a sequential cross‐coupling – bromination – cross‐coupling strategy.

Figure 2.24 Absorption (solid line, left), excitation spectrum (dashed line; λem = 629 mm) and corrected emission spectrum (solid line, right, λex = 360 nm) of 34 in CH3CN at 295 K. The corrected emission spectra of appropriate mononuclear model complexes are also shown: IrF4 = [Ir(F2ppy)2(phbpy)]+, Ir = [Ir(ppy)2(phbpy)]+, Ru = [Ru(bpy)2(phbpy)]²+.

Figure 2.25 Heterometallic complexes featuring linkers based on 1,3,5‐triethynylbenzene (37), spirobifluorene (38 and 39a,b) and triptycene (40).

Figure 2.26 Schematic representation of the photoinduced energy transfer processes occurring in 38, with the estimated energy levels of its constituent metallic units based on the properties of corresponding mononuclear model complexes [61].

Figure 2.27 Structural formulae of 41, 42ab, 43 and 44 that show evidence of emissive excited states localised primarily on the bridging ligands.

Figure 2.28 The PZn–Ir–PAu triad of Dixon et al. [73] that shows quantitative photoinduced formation of a charge‐separated state PZn+–Ir–PAu− with a lifetime of 450 ns.

Chapter 03

Figure 3.1 Early examples of LC iridium complexes using iridium(I).

Figure 3.2 Left: Chemical structure of complex 3. Right: Emission spectra of complex 3: (a) crystalline film (green), (b) mesophase film (yellow), (c) amorphous film (orange‐red), (d) dichloromethane solution; insets: real samples under UV illumination.

Figure 3.3 Mononuclear complexes and chloro‐bridged dimer using polycatenar ligands.

Figure 3.4 (a) Chemical structure of dimer 10; optical micrograph (on cooling) of (b) isomer 1 of 10 at 100°C; (c) isomer 2 of 10 at 60°C.

Figure 3.5 Left: Chemical structures of 11 and 12. Right: Emission spectra of acetonitrile gel of 11 and gels 11 + 12 with different molar ratios of 12/11 (λex = 356 nm, concentration of 11 = 25 mg mL−1).

Figure 3.6 Left: Chemical structures of iridium complexes 13–16. Middle: Gel phases obtained with complexes 13, 14, and 15 in water at 2.5% w/w. The gel formation was defined by the absence of flowing when the sample was turned upside down. Right: Schematic view of the proposed organization of iridium complexes in the gel phase; strands (solid gray) associate laterally into double rows incorporating water and counterions (gray dashed).

Figure 3.7 Chemical structures of complexes used for micelles.

Figure 3.8 Left: Chemical structures of complexes. Right: Normalized electroluminescence spectra for a series of ITO/pTPD/LB films of a mixture of 20 and 21 (30 ML)/Ba/Ag with ratios 1 : 0, 9 : 1, 4 : 1, and 0 : 1 of complex 20 and 21, respectively, in the LB films.

Figure 3.9 Left: Chemical structure of ion‐pair 22. Right: Spectra of compound 22 with anthraquinone loading (gray) and empty (black). Insets show fluorescence microscopy pictures of a filled crystal (a) and an empty crystal (b).

Figure 3.10 Soft0 salts based on dinuclear complexes, CD1.2A and CD2.2A.

Figure 3.11 Left: Chemical structure of ion‐pair 23 and 24. Right: Normalized emission spectra of 24 recorded in deaerated ACN at 298 K at different concentrations. λexc = 390 nm; A390 = 0.09. Insets are images of ACN solutions of 24 at different concentrations.

Figure 3.12 Chemical structure of ion‐pair 25.

Chapter 04

Scheme 4.1 Artificial photosynthesis can be categorized into several reactions. Each is thermodynamically uphill and requires multiple electrons.

Figure 4.1 The chemical structures of the blue dimer (a) and Bernhard’s iridium catalyst (b) for water oxidation. R1 = H or CH3 and R2 = H, Phenyl, F, or Cl.

Figure 4.2 The iridium‐based MOF, [Zn(L)2]‐3DMF‐5H2O (L = [Ir(ppy)(bpy‐dc)]+) shows decreased emission intensity with increasing concentrations of TNT (a). It was shown that the MOF PL decreases as the nitro content of aromatics increases (b).

Figure 4.3 The top view of the 2‐D layer CP‐1 (a). Stern‐Volmer quenching plots (b) show enhanced quenching for the coordination polymers (1 = Cp‐1, 2 = Cp‐2, 3 = Cp‐2 with different solvents) with respect to their homogeneous analogues (L1 = Ir[3‐(2‐pyridyl)benzoate]3 and L2 = Ir[4‐(2‐pyridyl)benzoate]3).

Figure 4.4 As more iridium content is confined within the MOF framework, larger PL intensity in the yellow region is observed to yield a white light‐emitting device (a). The [Ir(ppy)2(bpy)]+‐loaded MOF covering a blue LED is shown to emit light when excited by said LED (b).

Figure 4.5 The close proximity of metal centers in the ruthenium MOF (a) promotes active energy transport throughout the material. The emission decay kinetics show a shortening of Ru‐based excited‐state lifetimes upon increasing osmium concentration as well as a delayed growth of the osmium fluorescence edge, indicative of site‐to‐site energy migration (b).

Figure 4.6 The iridium catalyst in the MOF framework undergoes oxidation of the Cp* ligand yielding a precatalyst with a bound formate or acetate species (represented by X) that provides open coordination sites for water molecules to bind.

Figure 4.7 The insertion of POMs (a) and platinum nanoparticles (b) in the pores of photoactive MOFs promotes electron transfer to the catalyst and increases TON compared to the homogenous analogues.

Figure 4.8 The carbon dioxide reduction mechanism is shown with all the necessary steps including adsorption of light to yield an excited state, reduction of the catalyst, reduction absorbed CO2, and bond formation with a hydride to yield formate.

Chapter 05

Figure 5.1 Overview of the different categories of Ir(III)‐containing polymers and their photophysical features.

Scheme 5.1 Schematic representation of different general approaches for the synthesis of (co)polymers containing transition metal complexes.

Scheme 5.2 Schematic representation of the synthetic strategies utilized for the synthesis of cyclometallated Ir(III) complexes.

Scheme 5.3 Schematic representation of the synthesis of PDMS with an Ir(III) complex as end group.

Scheme 5.4 Schematic representation of the decoration of copolymers 4 and 8 with Ir(III) complexes via the formation of Schiff’s bases and subsequent reduction (a) as well as via CuAAC reaction (b).

Figure 5.2 Schematic representation of an early example for an Ir(III)‐containing polymer.

Scheme 5.5 Schematic representation of the synthesis of a metallocopolymer comprising Ir(III)‐terpyridine bis‐complexes within the side chains.

Scheme 5.6 Schematic representation of the synthesis of Ir(III)‐containing polymers having additional electron‐transport (ET) and hole‐transport entities as side chains.

Figure 5.3 Schematic representation of conjugated copolymers having quinolone‐based Ir(III) complexes in the side chain.

Scheme 5.7 Schematic representation of the synthesis of the diphenylphosphine‐substituted copolymer 18 (a), of a five‐coordinate bis‐cyclometallated Ir(III) complex according to Crabtree et al. (b) and of the Ir(III)‐containing polymer 19 (c).

Scheme 5.8 Schematic representation of the synthesis of polymers bearing Ir(III) centers complexed to the conjugated backbone. Two different approaches corresponding to methods II and V‐b are shown (see also Scheme 5.1).

Scheme 5.9 Schematic representation of the synthesis of a Ir(III)‐containing polymer 23 by coordination of Ir(III) centers to a conjugated backbone.

Figure 5.4 Schematic representation of the different types of polymer accessible via polymerization of Ir(III)‐containing monomers.

Figure 5.5 Schematic representation of some Ir(III)‐containing monomers for ROMP according to Weck et al.

Figure 5.6 Schematic representation of Ir(III)‐containing copolymer 25 as potent orange emitter.

Figure 5.7 Schematic representation of Ir(III)‐containing polymers 27 bearing dendron‐type substituents.

Figure 5.8 Schematic representation of the metal‐containing triblock copolymers 28 and 29. The TEM images of the self‐assembled micelles in aqueous media are also shown (scale bars: 200 nm) [60].

Figure 5.9 Schematic representation of copolymers 30 (a) and the binding of micellar 30 to STV‐coated magnetic beads (b). (c) The fluorescence spectra of 30 with (dashed lines) and without beads (solid lines) [61].

Scheme 5.10 Schematic representation of a polymer featuring an untypical type of Ir(III) complex as pending side chain.

Figure 5.10 Schematic representation of poly(3‐vinylcarbazole) 32N‐functionalized with blue‐emitting Ir(III) complexes.

Figure 5.11 (a) Schematic representation of cross‐linkable Ir(III) complexes 33 and (b) fabrication of a multilayered OLED device involving thermal cross‐linking of deposited complexes [81].

Figure 5.12 Schematic representation of the solution processing of the reactive components and their photo‐induced cationic cross‐linking [82].

Figure 5.13 Schematic representation of the microphase separation of copolymer 35 and its electroluminescence spectrum [85].

Scheme 5.11 Schematic representation of the synthesis of copolymer 36via NMP.

Scheme 5.12 Schematic representation of the synthesis of the Ir(III)‐containing copolymer 37via ATRP.

Figure 5.14 Schematic representation of the multicomponent metallopolymers 38 containing a photosensitizer and an electron relay (i.e., the photocatalytic system) as well as a solubility mediator [91].

Scheme 5.13 Schematic representation of the synthesis of Ir(III)‐containing conjugated polymers via metal‐catalyzed cross‐coupling reactions.

Figure 5.15 Schematic representation of conjugated polymer 39 with pending bis‐cyclometallated Ir(III) complexes.

Figure 5.16 Schematic representation of Ir(III)‐containing conjugated polymers 40 and 41 showing white emission.

Figure 5.17 Schematic representation of conjugated polymers 42–44 containing pending bis‐cyclometallated Ir(III) complexes.

Figure 5.18 Schematic representation of the multicomponent copolymer 45.

Figure 5.19 (a) Schematic representation of copolymers 46 featuring tetraphenylsilane moieties within the backbone. (b) Tapping‐mode AFM topographic image of copolymer 46a [102].

Figure 5.20 Schematic representation of conjugated polymers 47 having β‐diketonate units within the backbone.

Scheme 5.14 Schematic representation of the synthesis of polyfluorenes 48 endcapped with bis‐cyclometallated Ir(III)‐acac complexes.

Figure 5.21 Schematic representation of conjugated polymers 49–52 containing charged Ir(III) complexes coordinated to the backbone.

Figure 5.22 Schematic representation of conjugated polymer 53 containing 8‐hydroxyquinoline units as ancillary ligands within the backbone.

Scheme 5.15 Schematic representation of the synthesis of the conjugated copolymer 54 using a tris‐cyclometallated Ir(III) complex as comonomer.

Figure 5.23 Schematic representation of the Ir(III)‐containing copolymers 56–58 having a cyclometallating ligand within the backbone; the utilized Ir(III) complex monomer 55 is also shown.

Scheme 5.16 Schematic representation of the synthesis of conjugated polymers 59 and 60 featuring one Ir(III) complex within the backbone.

Figure 5.24 Schematic representation of copolymers 64–66 having Ir(III) complexes within the polymer main chain; the utilized Ir(III) complex monomers 61–63 are also shown.

Figure 5.25 Schematic representation of the white‐emitting copolymers 67 and 68.

Figure 5.26 Schematic representation of greenish‐blue‐emitting Ir(III)‐containing copolymers 69.

Scheme 5.17 Schematic representation of the synthesis of polyplatinynes via a polycondensation reaction (a) and of bis(ethynyl)‐functionalized Ir(III) complexes 70 as comonomer for this reaction (b).

Scheme 5.18 Schematic representation of the synthesis of the Ir(III)‐containing poly(phenylacetylene) 71.

Figure 5.27 Schematic representation of bis(bithiophene)‐substituted cationic Ir(III) complexes 72 as monomers for electropolymerization.

Scheme 5.19 (a) Schematic representation of the electropolymerization of metal‐NHC complexes. (b) Schematic representation of the reversible electrochromic behavior of polymer 73f [137].

Figure 5.28 (a) Schematic representation of the pyrrole‐functionalized Ir(III) complex 74 and the hybrid material poly‐74 MWCNT obtained by electropolymerization of 74 onto MWCNT‐coated electrodes. (b) SEM images of the MWCNTs before (top) and after the electropolymerization step [138].

Scheme 5.20 Schematic representation of the synthesis of hyperbranched Ir(III)‐containing polymers 75via a Yamamoto‐type polycondensation approach.

Figure 5.29 Schematic representation of the hyperbranched Ir(III)‐containing copolymer 76.

Scheme 5.21 Schematic representation of the synthesis of Ir(III)‐dendrimers 77.

Scheme 5.22 Schematic representation of the synthesis of the dendronized Ir(III) complex 78via direct tris‐cyclometallation of IrCl3.

Figure 5.30 Schematic representation of the synthesis of the dendronized Ir(III) complex 79via a post‐complexation modification strategy.

Chapter 06

Figure 6.1 The number of published journal reports (excluding patents) on iridium(III) complexes as of November 21, 2015.

Figure 6.2 (a) General synthetic scheme for neutral Ir(III) complexes via Nonoyama reaction [31]. (b) Homoleptic tris‐cyclometalated Ir(III) complex. (c) Heteroleptic tris‐cyclometalated Ir(III) complex. (d) Neutral heteroleptic bis‐cyclometalated Ir(III) complex. (e) Cationic heteroleptic bis‐cyclometalated Ir(III) complex.

Figure 6.3 (a) Simplified orbital diagram of a d⁶ complex in an octahedral field. (b) Electronic energy level diagram for a generic [Ir(C^N)2(L^X)]. Ligand is C^N, Ligand’ is L^X, MC is metal centered, LC is ligand centered, and LLCT and MLCT are ligand‐to‐ligand and metal‐to‐ligand charge transfer, respectively.

Figure 6.4 Molecular structures and abbreviation of a class of complexes with the general structure [Ir(C^N)2(acac)].

Figure 6.5 Molecular structures of the [Ir(X‐ppy)2(ptpy)], where X is either a F or a CF3.

Figure 6.6 Molecular structures and abbreviations of the phosphorescent [Ir(ppy)2(acac)] complexes bearing B(Mes)2 moieties.

Figure 6.7 (a) Molecular structures and abbreviations of the phosphorescent [Ir(dFppy)2(LX)]. (b) Suggested mechanism for color tuning by ILET (inter‐ligand energy transfer).

Figure 6.8 (a) Molecular structures and abbreviations used for the [Ir(C^N)2(L^L′)] complexes. (b) Plot of red/ox potentials versus emission energy, Eem(RT). The compounds are numbered as in Figure 6.8a. The asterisk (*) indicates an irreversible oxidation or reduction process; otherwise the electrochemical process is reversible or quasi‐reversible.

Figure 6.9 Molecular structures and abbreviations used for the Ir(C^N)2(L^X) complexes.

Figure 6.10 Different SMOLED architectures. (a) Monolayer architecture, (b) multilayer architecture, (c) p‐i‐n architecture, and (d) tandem architecture. EIL, electron‐injection layer; EML, emissive layer; ETL, electron‐transporting layer; HBL, hole‐blocking layer; HIL, hole‐injecting layer; HTL, hole‐transporting layer; IL, interconnecting layer.

Figure 6.11 Schematic representation of (a) Förster energy transfer, (b) Dexter energy transfer, (c) energy transfer in host–dopant systems, and (d) charge trapping for dopant emission in host–dopant system.

Figure 6.12 Structures of the selected examples of Ir(III) complexes.

Figure 6.13 Structures of selected hole (49, 51–54, 57) and electron (58–59) transport materials and ambipolar (60) materials.

Figure 6.14 Molecular structures and abbreviations used for the studied complexes [Ir(ppy)2(L^X)].

Figure 6.15 Molecular structures and abbreviations used for the studied complexes [Ir(ppy‐X)2(acac)].

Figure 6.16 Molecular structures and abbreviations used for the studied tris‐cyclometalated complexes Ir(ppy‐X)3.

Figure 6.17 Molecular structures and abbreviations used for the studied dendritic (d‐ppy‐SiPh4)3Ir 77, complex with mixed arylpyridine/aryltriazole ligands [Ir(dFptrBn)2(ppy)] 78, and heteroleptic iridium biscarbene complex [Ir(mpmi)2(pybi)] 79.

Figure 6.18 Molecular structures and abbreviations used for the studied red‐emitting tris‐cyclometalated Ir(III) complexes.

Figure 6.19 Molecular structures and abbreviations used for the studied red‐emitting [Ir(DBQ)2(acac)] 87 and [Ir(MDQ)2(acac)] 88.

Figure 6.20 Molecular structures and abbreviations used for the studied [Ir(phq)2(acac)]‐based complexes.

Figure 6.21 Molecular structures and abbreviations used for the studied bis‐ and tris‐cyclometalated Ir(III) complexes.

Figure 6.22 Molecular structures and abbreviations used for the carbazole‐based Ir(III) complexes.

Figure 6.23 Molecular structures of the dendritic Ir(III) complexes.

Figure 6.24 Molecular structures of [Ir(Ipt)2(bt)] 110.

Figure 6.25 Molecular structures and abbreviations used for the fluorinated Ir(III) complexes family.

Figure 6.26 Molecular structures and abbreviations of [Ir(X‐ppy)(pyPht)] complexes 115–118 and [Ir(diFppy)(pyX‐tr)] complexes 119–126.

Figure 6.27 Molecular structures and abbreviations of 1,2,3‐triazole‐based Ir(III) complexes 127–129 and internal salt complexes 130–135. ptps = 3‐(4‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐1‐yl)propane‐1‐sulfonate; ptmfb = trifluoro((4‐(pyridin‐2‐yl)‐1H‐1,2,3‐triazol‐1‐yl)‐methyl)borate; tpms = tris(pyrazolyl)‐methanesulfonate.

Figure 6.28 Molecular structures and abbreviations of 1,2,3‐triazole‐based Ir(III) complexes, and molecular structures and abbreviations of based Ir(III) 2′,4′‐difluoro‐2,3′‐bipyridine‐based complexes.

Figure 6.29 Molecular structures fac‐tris(1‐methyl‐5‐phenyl‐3‐n‐propyl‐1H‐[1,2,4]triazolyl)iridium(III) and its dendritic derivatives.

Figure 6.30 Molecular structures and abbreviations of [Ir(bptz)2(bdp)] 147 and [Ir(bptz)2(pdpit)] 148.

Figure 6.31 Molecular structures and abbreviations of [Ir(b5bpm)2(fppz)] 149.

Figure 6.32 Molecular structures and abbreviations of homo‐ and heteroleptic carbene‐based iridium complexes.

Figure 6.33 Molecular structures and abbreviations of homoleptic imidazole‐based iridium complexes 153–155 and for fac‐Ir(pmp)3156.

Figure 6.34 Structure of the complexes reported in Table 6.2.

Chapter 07

Figure 7.1 General schemes for the typical architectures of an OLED (left) and a LEEC (right).

Figure 7.2 Number of publications per year of iridium complexes employed in LEECs. Search from SciFinder (17 January 2017) using ‘LEC’ or ‘LEEC’ or ‘light‐emitting electrochemical cell’ and ‘iridium’ as keywords.

Chart 7.1 Structures of [Ir(ppy)2(bpy)][PF6], 1, and [Ir(ppy)2(dtbubpy)][PF6], 2, which are common archetype iridium complexes tested in LEEC devices.

Figure 7.3 Typical device architecture of an LEEC employing 1 as the emissive layer.

Figure 7.4 Colour tuning effects on iridium complexes. Solid arrows denote radiative processes while dashed arrows denote non‐radiative decay. In the red, increased non‐radiative decay rates according to the energy gap law processes become dominant. In the blue regime, thermal population of MC states becomes facile, leading to efficient quenching of the emission.

Figure 7.5 Reported CIE coordinates of LEECs fabricated from iridium complexes emitting green light in solution (data in Table 7.2). Of particular note are complexes 46, 47 and 59, which show a strong red shift in emission of the device, and also complex 22, which has CIE coordinates very close to the ideal green coordinate (0.30, 0.60).

Figure 7.6 Green‐emitting iridium complexes bearing hydrophobic substituents on the ancillary ligand.

Figure 7.7 Selected examples of green‐emitting iridium complexes bearing fluorinated cyclometalating ligands.

Figure 7.8 Selected examples of green‐emitting iridium complexes bearing phenanthroline‐type ancillary ligands.

Figure 7.9 Bright green‐emitting iridium complexes bearing bulky ancillary ligands.

Figure 7.10 Multi‐fluorinated green‐emitting iridium complexes studied by Baranoff et al.

Figure 7.11 3‐Trifluoromethyl‐substituted complexes.

Figure 7.12 Iridium complexes bearing cyclometalated 2,3′‐bipyridines.

Figure 7.13 Iridium complexes bearing ppz C^N ligands.

Figure 7.14 Cyclometalated 1‐(4‐(methylsulfonyl)phenyl)pyrazole complexes.

Figure 7.15 Green‐emitting pyridylimidazole complexes.

Figure 7.16 Green‐emitting triazole complex.

Figure 7.17 Green‐emitting tetrazole complexes.

Figure 7.18 Green‐emitting aryl‐1,3,4‐oxadiazole complexes.

Figure 7.19 Green‐emitting pyridyl‐1,2,4‐oxadiazole complexes.

Figure 7.20 Iridium complex bearing a cyclometalating thiophenylpyridine ligand.

Figure 7.21 Phenanthroline‐type complexes.

Figure 7.22 Ppz complexes exhibiting intramolecular π‐stacking interactions.

Figure 7.23 Asb complexes exhibiting intramolecular π‐stacking interactions.

Figure 7.24 Cyclometalated thiophenylpyridine iridium complex with an intramolecular π‐stacking interaction.

Figure 7.25 Fluorine‐free complexes exhibiting intramolecular π‐stacking interactions.

Figure 7.26 Carbazole‐functionalised complex.

Figure 7.27 Bimetallic green‐emitting complex.

Figure 7.28 Reported CIE coordinates of LEECs fabricated from iridium complexes emitting blue light (λmax < 500 nm) in solution (data in Table 7.3). The deepest blue‐emitting device reported to date, employing complex 68, is significantly red‐shifted compared with what is defined as blue in the RGB colour space.

Figure 7.29 [Ir(ppy)2(bpy)]+‐type blue‐emitting complexes.

Figure 7.30 Phenanthroline blue‐emitting complexes.

Figure 7.31 Multiple‐charged, blue‐emitting iridium complex bearing charged phosphonium units.

Figure 7.32 Blue‐emitting iridium complexes bearing pyridylpyrazole ancillary ligands.

Figure 7.33 Blue‐/blue‐green‐emitting pyridylpyrazole complexes bearing sulfonated cyclometalating ligands.

Figure 7.34 Blue‐/blue‐green‐emitting dimethylpyridylpyrazole complexes bearing sulfonated cyclometalating ligands.

Figure 7.35 Intramolecular π‐stacked complexes bearing a 2‐(3‐phenyl‐1H‐pyrazol‐1‐yl)pyridine ligand.

Figure 7.36 Intramolecular π‐stacked complexes bearing a 2‐(1‐phenyl‐1H‐pyrazol‐1‐yl)pyridine ligand or fluorinated analogues thereof.

Figure 7.37 Iridium complexes bearing N‐(2,4‐difluorophenyl)pyrazole (dFppz) as the cyclometalating ligand.

Figure 7.38 Iridium complexes bearing 2‐(4‐ethyl‐2‐pyridyl)‐1H‐imidazole as the ancillary ligand.

Figure 7.39 Iridium complexes bearing ‘protected’ imidazole rings.

Figure 7.40 Iridium complexes bearing pyridyl‐1,2,3‐triazole ancillary ligands.

Figure 7.41 Iridium complexes bearing pyridyl‐1,2,4‐triazole ancillary ligands.

Figure 7.42 Iridium complex bearing a 5‐(4,6‐difluorophenyl)‐1,2,3‐triazole cyclometalating ligand.

Figure 7.43 Complexes containing triazoles within the C^N and N^N ligand frameworks.

Figure 7.44 Blue‐green‐emitting iridium complexes bearing cyclometalating oxadiazole ligands.

Figure 7.45 Iridium complexes bearing pyridylbenzimidazolium NHC ancillary ligands.

Figure 7.46 Iridium complexes bearing pyridylimidazolium NHC ancillary ligands.

Figure 7.47 Iridium complexes bearing bis‐imidazolium NHC ancillary ligands.

Figure 7.48 Blue‐emitting iridium complex bearing a strong field P^P ancillary ligand.

Figure 7.49 Reported CIE coordinates of LEECs fabricated from iridium complexes emitting what we have nominally defined as yellow light (560 nm < λPL < 600 nm) in solution (data in Table 7.3). Champion LEECs in terms of efficiency (119, EQE = 6.1%) and device lifetime (133, t1/2 = 2000 h) are highlighted. CIE coordinates are not reported for many of the LEECs listed in Table 7.4, but of the reported values, none of these are close to ‘yellow’ (CIE: 0.44, 0.55). Complexes discussed previously that are very close to this point include 3 (CIE: 0.44, 0.55), 40 (CIE: 0.44, 0.54) and 44 (CIE: 0.44, 0.52).

Figure 7.50 [Ir(ppy)2(bpy)]+ complexes bearing various alkyl substituents on the bpy.

Figure 7.51 [Ir(ppy)2(bpy)]+ complex bearing multiple hydrophobic substituents.

Figure 7.52 Iridium complexes bearing substituted phenanthroline ancillary ligands.

Figure 7.53 Iridium complex bearing a fused phenanthroline‐imidazole ancillary ligand.

Figure 7.54 Iridium complexes bearing alkyl substituted diazafluorene ancillary ligands.

Figure 7.55 [Ir(ppy)2(bpy)]+ complexes bearing alkyl ammonium‐substituted bpy ligands.

Figure 7.56 Iridium complexes bearing imidazole or imidazolium ancillary ligands.

Figure 7.57 Anionic complexes used LEECs.

Figure 7.58 Archetype intramolecular π‐stacked emitters.

Figure 7.59 Multiple intramolecularly π‐stacked emitters.

Figure 7.60 Intramolecular π‐stacked emitters bearing naphthyl and pyridyl π‐stacking moieties.

Figure 7.61 Intramolecular pyridyl π‐stacked emitters bearing appended phenolic (129), anisolic (130), anilinic (131) and thioanisolic (132) moieties.

Figure 7.62 Intramolecular π‐stacked emitters bearing alkylated phenylpyrazole cyclometalating ligands.

Figure 7.63 Iridium complexes appended with charge transport units.

Figure 7.64 Iridium complexes appended with bulky units of increasing size.

Figure 7.65 Bimetallic yellow‐emitting complex.

Figure 7.66 Reported CIE coordinates of LEECs fabricated from iridium complexes emitting what we have nominally defined as orange‐red/red light (λPL > 599 nm) in solution (data in Table 7.4). Notable LEECs include complex 171, which shows good efficiency (EQE = 3.3%) and closeness to the red point (CIE: 0.60, 0.30; CIE171: 0.65, 0.34) (171, EQE = 3.3%). Complex 172 is the reddest LEEC reported (CIE: 0.71, 0.28). We note also that the champion red LEEC is the oxadiazole complex 47, which shows very high device efficiency (EQE = 9.5%), and is orange‐red in colour (CIE: 0.59, 0.40).

Figure 7.67 [Ir(ppy)2(bpy)]+‐type emitters showing high device stability.

Figure 7.68 [Ir(ppy)2(bpy)]+‐type emitters with extended bpy ligands.

Figure 7.69 Red emitting [Ir(ppy)2(bpy)]+‐type complex bearing multiple MeO‐substituents on the phenyl ring of the C^N ligand.

Figure 7.70 [Ir(ppy)2(bpy)]+‐type emitter appended with a charged unit for decreasing device turn‐on time.

Figure 7.71 Red emitting iridium complexes bearing five‐membered heterocycles.

Figure 7.72 Red emitting iridium complex bearing a thiophenylpyridine cyclometalating ligand.

Figure 7.73 Archetypal orange‐red emitting intramolecularly π‐stacked iridium complex.

Figure 7.74 Intramolecularly π‐stacked complexes using five‐membered π‐stacking rings.

Figure 7.75 Intramolecularly π‐stacked complexes bearing diphenyl‐bipyridyl‐type ligands.

Figure 7.76 Intramolecularly π‐stacked complexes bearing brominated substituents.

Figure 7.77 Intramolecularly π‐stacked complexes bearing strong electron‐donating substituents.

Figure 7.78 Intramolecularly π‐stacked complexes bearing thiophenyl rings.

Figure 7.79 Intramolecularly π‐stacked complex bearing a terpyridine ligand.

Figure 7.80 Complexes bearing multiple intramolecular π‐stacking interactions.

Figure 7.81 Iridium complex bearing carbazolyl charge‐transporting units.

Figure 7.82 Supramolecular complex bearing an iridium and a perylenediimide chromophore.

Figure 7.83 Red emitting monomer complex and its corresponding polymer.

Chapter 08

Figure 8.1 Schematic diagram describing the electron transfer reactions responsible for emission during annihilation ECL of Ir(ppy)3.

Figure 8.2 Schematic diagram describing the electron transfer reactions responsible for emission during a co‐reactant ECL reaction involving Ir(ppy)3 and tri‐n‐propylamine (TPA).

Figure 8.3 The number of published journal reports per year (excluding patents and reviews) concerning electrochemiluminescence as of 21 April 2015. Iridium ECL that is the topmost series of the main graph is also plotted separately in the inset; ruthenium ECL, including all commercial assays, is the middle series and ECL based on all other or unspecified electrochemiluminophores is the lowest series. It should be noted that, in addition to organic ECL, quantum dot ECL and ECL from other metal complexes, the lower series likely contains a significant number of biological studies where a commercial electrochemiluminescent ruthenium complex was used but not mentioned explicitly.

Figure 8.4 The first attempts at achieving ECL from iridium‐based complexes explored a variety of different structures. (a) [Ir(phen)2Cl2]+ from Ref. [6], (b) Ir(ppy)3 from Ref. [32] and (c) [Ir(COD)(μ‐L)]2 from Ref. [33], which is a unique example of ECL observed in iridium(I) complexes.

Figure 8.5 The relationship between log (ΦECL) and ΔGES for [Ir(ppy)3]+/A− systems, where A− is a reduced aromatic organic acid, showing the approach to the photoluminescent quantum yield (dotted line).

Figure 8.6 Electrochemiluminescent iridium complexes of the type Ir(C^N)2(acac), where C^N is 1–14 earlier, used by Kapturkiewicz and co‐workers to study the energetics of ECL reactions in Refs [51–53].

Figure 8.7 Intense ECL‐emitting iridium complexes with 2‐phenylpyridine or 2‐phenylquinoline cyclometallating ligands and a variety of ancillary ligands. (a) [Ir(ppy)2(bpy)]+, (b) Ir(pq)2(3‐iq), (c) Ir(pq)2(pic), (d) Ir(pq)2(quin), (e) [Ir(ppy)2(phen)]+, (f) Ir(pq)2(dbm), (g) Ir(pq)2(tmd) and (h) Ir(pq)2(acac).

Figure 8.8 Kim’s postulated requirements for efficient ECL generation. (a) A high oxidation potential is required to remove an electron from the TPA HOMO and efficiently generate TPA radical cation. (b) The LUMO of the emitter should be lower than that of the TPA• donor.

Figure 8.9 (a) Ir(btp)2(acac) and (b) F(Ir)pic, the iridium luminophores used in an early attempt at immobilising insoluble iridium complexes on an electrode surface.

Figure 8.10 (a) Ir(pq)2(N‐phMA) is used to modify electrode surfaces. There is a remarkable difference in the reproducibility of the ECL signal for electrodes coated with iridium complex only (b) and those coated with the complex/MWNT films (c).

Figure 8.11 Encapsulation of a hydrophobic iridium complex within a silica nanoparticle allows for immobilisation on an electrode surface and aqueous ECL analysis.

Figure 8.12 Azacrown appended iridium complexes (a) and (b) for ECL detection of metal cations and underivatised parent complex (c). A typical response is shown in (d).

Figure 8.13 (a) The ECL behaviour of Ir(pq)2(N‐phMA)‐modified electrode in the absence and presence of ammonium and (b) results of the ECL test of meat decomposition over time.

Figure 8.14 The ECL detection of ammonia with various iridium(III) complexes (c) where 1 is Ir(ppy)2(acetylaniline), 2 is Ir(pq)2(N‐phMA), 3 is Ir(ppy)3 and 4 is Ir(pq)2(acac). (a) and (b) show the voltammetric responses and calculated MO energies respectively.

Figure 8.15 DNA‐based assay used to detect cancer cells using the ECL‐active complex [Ir(ppy)2(dcbpy)]+.

Figure 8.16 (a) The cellular sandwich assay allowing single cell detection utilising [Ir(ppy)2(dcbpy)]+. (b) The ECL response is linear across a wide range.

Figure 8.17 [Ir(pq)2(bpy‐sugar)]+ (a), schematic describing the ECL‐based thrombin detection system (b) and typical sensor response (c).

Figure 8.18 (a) [Ir(ppy)2(dcbpy)]+ used in an ECL quenching study to detect very low levels of FB1 via a highly selective DNA recognition and binding system. (b) Formation and operation of the ECL ‘aptasensor’. (c) ECL quenching provided a very low limit of detection.

Figure 8.19 Analysis of water content in organic solvents based on co‐reactant ECL reaction of Ir(pq)2(acac) with hydroxyl ions.

Figure 8.20 Iridium dimer [Ir(pq)2Cl]2 used in a dual channel ‘lab‐on‐a‐molecule’ sensor exploiting both PL and ECL modes of sensing.

Figure 8.21 (a) [Ir(pq)2(FcC2phenC2Fc)]+ and (b) relative energy levels involved in ECL emission.

Figure 8.22 (a) Triple‐channel ‘lab‐on‐a‐molecule’ detection of various amino acids using iridium complex and (b) ECL quenching response of the same complex to varying concentration of tryptophan.

Figure 8.23 The imidazole functionalised anion sensitive (a) and insensitive (b) iridium complexes. (c) The proposed binding mode of the acetate anion to the oxidised iridium complex enhancing ECL response.

Figure 8.24 Water‐soluble charged iridium complexes (a) Ir(ppy)2(pytl‐Me)]+, (b) [Ir(ppy)2(pytl‐ada)]+, (c) [Ir(ppy)2(pytl‐βCD)]+ and (d) [Ir(dfppy)2(pytl‐ada)]+.

Figure 8.25 Use of polar groups such as sulfonates in (a) [Ir(ppy)2(BPS)]− and sugars in (b) [Ir(pq)2(bpy‐sugar)]+ impart improved solubility to electrochemiluminescent iridium complexes.

Figure 8.26 Series of ECL‐active iridium complexes with sulfonated ancillary ligand to achieve aqueous solubility whilst tuning the photophysical and electrochemical properties via the main ligand. (a) [m‐m′Ir(ppy)2(BPS)]−, (b) [m‐m′Ir(dfppy)2(BPS)]−, (c) [m‐m′Ir(bt)2(BPS)]−, (d) [m‐m′Ir(piq)2(BPS)]−, (e) [p‐m′Ir(ppy)2(BPS)]−, (f) [p‐m′Ir(dfppy)2(BPS)]−, (g) [p‐m′Ir(bt)2(PBS)]− and (h) [p‐m′Ir(piq)2(BPS)]−.

Figure 8.27 Encapsulation of an insoluble iridium complex within a silica‐PEG nanoparticle is an alternate strategy for improving aqueous ECL.

Figure 8.28 Electrochemiluminescent dendrimeric analogue of Ir(ppy)3 offering partial protection against quenching due to dissolved oxygen and parasitic side reactions.

Figure 8.29 Ir(tpy)2(pic) provided efficient ECL as well as a blue shift in emission colour.

Figure 8.30 Despite favourable electrochemistry, these thiophene‐based iridium complexes displayed poor ECL performance due to unfavourable photophysical properties. R1 = H or Me and R2 = H, CHO or Me.

Figure 8.31 (a)–(d) Careful selection of substituents used with [Ir(phtl)2(bpy)]+ and related 1,2,3‐traizole‐based iridium complexes has led to highly tuneable emission colour whilst maintaining intense ECL emission.

Figure 8.32 (a)–(c) Incorporation of co‐reactant‐type electroactive moieties into the architecture of a series of iridium complexes of the type [(C^N)2Ir(dmabpy)]+ resulted in self‐enhanced ECL.

Figure 8.33 The use of non‐traditional ligands allowed for selective colour tuning towards the blue/green whilst simultaneously achieving ECL efficiency of up to 13 times that of [Ru(bpy)3]²+. (a) Ir(FPP)2(acac), (b) Ir(FBPI)2(acac), (c) Ir(FBPI)2(pic), (d) Ir(FBPI)2(pmp) and (e) Ir(MDX)2(acac).

Figure 8.34 (a)–(e) Although amidate‐based ancillary ligands did not lead to intense ECL emission, these iridium complexes have helped to better understand the energy requirements for ECL process.

Figure 8.35 A series of blue‐shifted ECL emitters used to investigate the best strategy for obtaining efficient blue ECL. Complex numbers correspond to data in Table 8.1: (3) Ir(ppy)2(ptp), (4) [Ir(ppy)2(ptb)]+, (6) Ir(dfppy)2(ptp), (7) [Ir(dfppy)2(ptb)]+, (8) Ir(ppz)3 and (9) Ir(pmi)3.

Figure 8.36 Dependence of ECL intensity on ΔG for co‐reactant ECL reaction A leading to the excited state and reaction B leading to ground state. Data in (a) and (b) from DFT calculations. Data in (c) and (d) from electrochemical and spectroscopic experiments. ΔG values were calculated as E(LUMO M+) − E(HOMO TPA•) in (a) and as E(HOMO M+) − E(HOMO TPA•) in (b). In (c) and (d) ΔG values were calculated from the data in Table 8.1 using Equations 8.31 and 8.32 and for (c) and (d), respectively.

Figure 8.37 (a) The ECL ‘wall of energy sufficiency’ plot (for TPA co‐reactant) as proposed by Hogan and co‐workers provides a convenient visualisation of the effect of oxidation potential on the thermodynamics of ECL reactions as a function of emission colour and a useful way to quickly estimate ECL performance. (b) Energy diagram for energy sufficient and energy insufficient co‐reactant ECL reactions, where EES is the energy of the excited state.

Figure 8.38 (a) 3D ECL graph of ECL intensity as a function of applied potential and emission wavelength, created by an automated acquisition of ECL spectra throughout the forward sweep of a cyclic voltammogram; and (b) comparative photoluminescence excitation–emission matrix. Conditions: (a) 0.1 mm [Ir(dfppy) 2(BPS)]− and 0.01 mm [Ru(bpy)2(L)]²+ in 1 : 1 v–v water–acetonitrile with 10 mm TPA; (b) 0.05 mm [Ir(dfppy)2(BPS)]− and 0.025 mm [Ru(bpy)2(L)]²+ in 1 : 1 v–v water–acetonitrile.

Figure 8.39 3D ECL plots for (a) a mixture of Ir(ppy)3 and [Ru(bpy)2(L)]²+ and (b) Ir(ppy)3 and Ir(dfppy)3, using TPA as co‐reactant in acetonitrile. (c) Photographs of the ECL at the working electrode surface for these two systems as the potential was varied from 0.18 to 1.13 V (vs. Fc⁰/+), with the same exposure time used for each image.

Figure 8.40 3D ECL plot of a mixture of three metal complexes: Ir(dfppy)2(ptp) (blue emission at high potentials), Ir(ppy)3 (green emission at low potentials) and [Ru(bpy)2(dm‐bpy‐dc)]²+ (red emission at intermediate and high potentials) in acetonitrile, using TPA as the co‐reactant.

Figure 8.41 (a) Non‐Kekulé structured polynuclear metallocomplex capable of potential dependant ECL. (b) Normalised ECL (0–1.8 V) and PL of Ir–Ru–Ir. (c) ECL emission of Ir–Ru–Ir (10 μM) in TPA/ACN using different sweep ranges.

Figure 8.42 (a)–(d) ECL spooling techniques assist in examining ECL spectral distribution as a function of applied potential and gain mechanistic information.

Figure 8.43 The ECL response of [Ru(bpy)3]²+ varies with the ratio of [Ir(dfppy)2(bpy)]+ present in the emissive layer of the device.

Figure 8.44 The ability to access the emissive properties of iridium complexes via ECL negates the need for optical excitation; this opens up the ability to use photoactive switching technology without changing the state of the switch.

Chapter 09

Figure 9.1 Z‐scan images of living KB cells incubated with complex 2e (20 μM, 30 min).

Figure 9.2 Fluorescence microscopy images of live CHO cells co‐stained with complex 3a (10 μM, 1 h) and Hoechst (350 nM, 5 min), using pulsed excitation at 355 nm (pulse length = ca. 4 ns). (a) No delay between laser pulse and image acquisition. (b) The image recorded after a delay of 10 ns.

Figure 9.3 Confocal microscopy images of HeLa cells co‐stained with complexes 7 [Ir(pppy)2(Ph2‐phen)]+, [Ir(pppy‐C4)2(phen)]+, and [Ir(ppy‐C4)2(bpy‐biotin)]+, and fluorescent MitoTracker. The emission at 570 ± 50 and 670 ± 20 nm was collected for the complexes and fluorescent dye, respectively.

Figure 9.4 a,b,f,g) Confocal luminescence images, c,h) PLIM images, and d,e,i,j) TGLI images (delayed time = 200 or 500 ns) of live HeLa cells incubated with the nanoprobe (200 μg mL−1) at 37°C for 2 h and then under 2.5% or 21% O2 at 37°C for 1 h. Excitation wavelength = 405 nm. All the images share the same scale bar of 30 μm.

Figure 9.5 Confocal microscopy images of HeLa cells dosed with complex 14 (2 μM, 2 h) after preincubation under 20 and 2.5% O2 conditions for 24 h at 37°C. (a) λem = 460–510 nm and (b) λem > 610 nm.

Figure 9.6 Emission spectral changes of complex 17 (8.14 × 10−5 M) in CH3CN/H2O (4 : 1, v/v, pH 7.2) in the presence of Cys (0–50 equiv.).

Figure 9.7 Emission spectral changes of [SiO2‐Ir(F2ppy/pic)@MSN‐19a] in water in the presence of Cys (0–70 equiv.).

Figure 9.8 Emission spectral changes of complex 25 (20 μM) in aerated CH3CN in the presence of Hg(II) (0–40 μM). Inset: emission titration curve of the complex with Hg(II).

Figure 9.9 Luminescence microscopy images of HeLa cells incubated with complex 28 (20 μM, 1 h) in the (a) absence and (b) presence of HOCl (50 μM, 0.5 h).

Figure 9.10 Emission spectral traces of complex 30 (5 μM) in aerated potassium phosphate buffer (50 μM, pH 7.4)/DMSO (99 : 1, v/v) at 298 K in the presence of NOC‐7 (0–25 μM).

Figure 9.11 Confocal microscopy images of HeLa cells incubated with complexes 32 and 33 (10 μM) in DMSO/PBS (pH 7.4, 1 : 99, v/v) for 10 min at 37°C (λex = 488 nm, λem = 520 ± 20 nm).

Figure 9.12 Confocal microscopy images of fixed MDCK cells treated with complexes 35a–35c (5 μM) at room temperature for 30 min.

Figure 9.13 Confocal microscopy images of HeLa cells treated successively with complex 37a or 37b ([Ir] = 2 μM) at 37°C for 2 h, PBS containing 3% paraformaldehyde, antigolgin‐97 (human) mouse IgG1 (1 µg/ml, 1 h), and Alexa 635 goat antimouse IgG (H + L) (10 µg/ml, 30 min).

Figure 9.14 Confocal microscopy images of 3T3 cells treated with complex 43 (5 μM) acquired at different time points. Yellow areas indicate co‐localization of MitoTracker Red and the complex in mitochondrion structure. Scale bar: 25 µm.

Figure 9.15 Confocal microscopy images of MDAMB231CXCR4+ cells incubated with complexes (a) 47a, (b) 47b, and (c) 47c ([Ir] = 1 μM, 1 h at 4°C).

Figure 9.16 Emission spectra of complexes (a) 52a, (b) 52b, and (c) 52c ([Ir] = 190 μM) in HEPES buffer in the presence of heparin (0–15.5 μM) (λex = 365 nm). Inset of (a): solutions of complex 52a under handheld UV‐lamp excited at 365 nm ([heparin] = 0, 3.9, and 15.5 μM from left to right). Insets of (b) and (c): solutions of complex 52b and 52c, respectively, under handheld UV‐lamp excited at 365 nm ([heparin] = 0 (left) and 15.5 μM (right)).

Figure 9.17 (a) Emission spectra of complex 60a (10 μM) in degassed DMSO/100 mM buffer (from pH 4 to 10) at 298 K. (b) Photograph showing solutions of the complex (10 μM) in degassed DMSO/100 mM buffer (from pH 4 to 10) at 298 K. Excitation at 366 nm.

Figure 9.18 Cytotoxicity of complexes 62a–62e and cisplatin toward HeLa cells upon incubation in the dark for 12 h. The cells were further incubated in the dark (left bar of each concentration) or irradiated at 365 nm (right bar of each concentration) for 30 min.

Chapter 10

Figure 10.1 Schematic diagram of a chemical sensor.

Figure 10.2 Most relevant Ir(III) complexes used as oxygen probes.

Figure 10.3 Most relevant Ir(III) complexes containing S^S ancillary ligands, which have been used as optical probes for determining Hg(II).

Figure 10.4 Most relevant Ir(III) complexes containing O^O ancillary ligands that have been used as optical probes for determining Hg(II).

Figure 10.5 Most relevant Ir(III) complexes containing DPA, which have been used as optical probes for determining Zn(II).

Figure 10.6 Most relevant Ir(III) complexes for optical determination of pH.

Figure 10.7 Most relevant Ir(III) complexes for optical determination of F−.

Figure 10.8 Cyclometalated Ir(III) complexes containing one biotin moiety for optical determination of avidin.

Figure 10.9 Ir(III) complexes containing bipyridine estradiol conjugates for optical determination of estrogen receptors.

Figure 10.10 Chemical structure of the most relevant Ir(III) complexes used in the development of optical oxygen sensing films.

Chapter 11

Figure 11.1 (a) Jablonski diagram of photophysical processes undertaken by the transition metal photocatalyst upon visible‐light irradiation. (b) The redox transformations possible with Ir(ppy)3 photocatalyst. (c) A compilation of electrochemical data of the four archetypical photocatalysts employed.

Figure 11.2 Conventional methods for homoleptic and heteroleptic complex synthesis.

Figure 11.3 Single‐electron oxidation of amines greatly reduces the bond strength of adjacent C–H bonds, as evidenced by the dramatic reduction in pKa and BDE.

Figure 11.4 Aza‐Henry reaction with tetrahydroisoquinoline to demonstrate amine oxidation and functionalization.

Figure 11.5 A compilation of all the variants of tetrahydroisoquinoline functionalization strategies using photoredox catalysis as the initial substrate activator. Illustrated in each direction are the different transformations applied with the common tetrahydroisoquinolinium intermediate (center).

Figure 11.6 Oxidation of N‐methylmorpholine for access toward complex pharmaceutical scaffolds.

Figure 11.7 Oxidation of para‐methoxybenzyl ethers in the presence of water allows for a mild, visible light‐controlled deprotection strategy.

Figure 11.8 (a) The relationship between redox potential of alkyl halide substrate and chosen photocatalyst following an increase in reductant strength from left to right. (b) Alkyl and aryl deiodination strategy developed by Stephenson. (c) Proposed mechanism involving the reductive quenching cycle of Ir(ppy)3.

Figure 11.9 Asymmetric ketyl cyclization catalyzed by heteroleptic Ir(III) photocatalyst and controlled with chiral phosphoric acid.

Figure 11.10 Stephenson and coworker’s strategy toward the depolymerization of lignin. A two‐step redox‐neutral strategy that relied on a key reductive Ir(III) photoredox‐catalyzed reduction of weak α‐etheral bond in β‐O‐4 model lignin substrate. The proposed mechanism evokes an oxidative quenching cycle reliant upon N,N‐diisopropyl amine‐formic acid terminal reductant.

Figure 11.11 Atom transfer radical addition of trifluoromethyl iodide with inactivated terminal alkenes. The transformation is proposed to involve both catalytic and radical propagative mechanisms.

Figure 11.12 Atom transfer radical addition of a trifluoromethyl radical generated from Umemoto’s reagent (88) and trapped with different oxygen nucleophiles (alcohols and water).

Figure 11.13 Atom transfer radical addition of a trifluoromethyl radical generated from Togni’s reagent (93) and trapped with dimethyl sulfoxide (DMSO). DMSO is a transient trap and subsequently leads to benzylic oxidation and ketone products.

Figure 11.14 A summary of the atom transfer radical addition strategies employed to generate a variety of functional groups.

Figure 11.15 Atom transfer radical addition for γ‐lactone formation.

Figure 11.16 Divergent strategies of functionalizing alkynes utilizing trifluoromethyl radical transfer addition to generate vinyl‐trifluoromethyl iodides, vinyl trifluoromethanes, and phenyl‐trifluoromethyl alkenes. Each strategy is controlled by the stoichiometry and identity of amine employed.

Figure 11.17 Atom transfer radical addition of α‐amino radicals with phenyl vinyl sulfones to generate α‐vinyl substituted amines.

Figure 11.18 Atom transfer radical addition of alkyl radicals arising from the reduction of iodosobenzene diacetates with isonitriles to generate nitrogen‐containing heterocycles.

Figure 11.19 Difluoroacetamide functionalization of electron‐rich arenes.

Figure 11.20 Redox‐neutral coupling of aryl halides with other arenes to form biphenyl motifs.

Figure 11.21 Redox‐neutral coupling of α‐amino radicals with long‐lived cyanoarene radicals to form α‐arylated amines.

Figure 11.22 Dual catalysis approach combining visible light photoredox catalysis with iminium catalysis to generate enantiopure trifluoromethylated aldehydes.

Figure 11.23 Dual catalysis strategy employing photoredox catalysis and organocatalysis to couple benzylic radicals of imines and methoxy ethers.

Figure 11.24 Dual catalysis strategy employing photoredox catalysis and nickel(II) catalysis to couple benzylic radicals with aryl halides.

Figure 11.25 Dual catalysis strategy employing photoredox catalysis and cationic gold(I) catalysis to couple diazonium or aryl iodonium salts with alkenes in the presence of an oxygen nucleophile.

Figure 11.26 Strain‐driven amine oxidation–fragmentation strategy to access three different indole alkaloids commercially available (+)‐catharanthine.

Chapter 12

Figure 12.1 An experimental setup and mechanistic pathways for photocatalytic hydrogen evolution in homogeneous systems. Both the reductive (a) and oxidative (b) quenching mechanisms are illustrated for the simplest three‐component system. The four‐component variant is only shown with its most common mechanism, oxidative quenching (c).

Figure 12.2 Synthesis of photosensitizer 2‐1 through the general two‐step pathway used for all bis‐cyclometalated iridium complexes of the form [Ir(C^N)2(N^N)]+.

Figure 12.3 Jablonski diagram showing the electronic structure of bis‐cyclometalated iridium complexes. The main energy states are labeled in bold with contributing orbitals listed below in gray.

Figure 12.4 (a) Experimental (black, solid line) and predicted (blue, dashed line) UV–Vis absorbance spectra for 2‐1 in acetonitrile. The predicted spectrum is shown with oscillator strengths and was calculated via TD‐DFT using a B3LYP functional with the LANL2DZ basis set. The inset magnifies the low energy portion of the spectra to show a low intensity transition near 470 nm, which is not readily predicted. Roman numerals label the principal absorbances in the spectra. (b) Energy level diagram showing calculated orbitals along with transitions representing a major type of excitation in each labeled spectral region. Note that the transition shown for region I only indicates a predicted spin‐allowed component. (c) Cyclic voltammogram of 2‐1 showing the redox behavior typical for complexes of the form [Ir(C^N)2(N^N)]+. The voltammogram was collected at 100 mV s−1 in acetonitrile.

Figure 12.5 Commonly used ancillary (N^N) and cyclometalating (C^N) ligands for synthesizing iridium photosensitizers for H2 generation. The parent compound, 3‐1, is depicted above.

Figure 12.6 Select non‐noble metal‐based WRCs used with iridium photosensitizers.

Figure 12.7 Phenylazole‐based iridium photosensitizers used for photocatalytic water reduction. 3‐4 performs better than the other derivatives.

Figure 12.8 Family of Ir PSs based on 2‐phenylbenzothiazole C^N ligands. 3‐9 and 3‐10 outperform the other complexes and can generate H2 through both homogeneous and heterogeneous means.

Figure 12.9 Coumarin‐based Ir PSs employed for photocatalytic water reduction. All complexes (except 3‐15) generate more H2 than the standard iridium PS 3‐1.

Figure 12.10 Family of Ir PSs containing quinoline‐based cyclometalating ligands. Increasing conjugation has a negative impact on H2 evolution, with only 3‐16 performing better than the reference [Ir(ppy)2(dmbpy)]+.

Figure 12.11 Iridium photosensitizers employing benzamidinate‐based ancillary ligands. These complexes effectively drive water reduction via oxidative quenching.

Figure 12.12 (a) Novel 1,4‐bis‐imine ancillary ligands used for synthesizing iridium photosensitizers. Unfortunately, none of the resulting complexes are effective in driving water reduction. (b) Bpy bearing bulky substituents, dTPS‐dphbpy, which leads to improved stability of the resulting iridium PS.

Figure 12.13 Major classes of ancillary ligands that have been installed in iridium PS in order to tether the PS to a WRC for photocatalytic H2 generation.

Figure 12.14 Iridium photosensitizers utilizing strong tridentate coordination to achieve higher photostability in coordinating solvent as compared with the popular [Ir(C^N)2(N^N)]+ structure. MeO = methoxy, diMeO‐C6H5 = 2,4‐dimethoxyphenyl.

Figure 12.15 Tris‐cyclometalated hydrogen‐evolving iridium PS that is either (a) heteroleptic or (b) homoleptic.

Figure 12.16 Dinuclear complexes employed for photocatalytic H2 production.

Chapter 13

Figure 13.1 Molecular structures of the cyclometalated iridium complexesreported by Bernhard and coworkers.

Figure 13.2 Structures of chloro‐bridged dimers [{(C^N)2Ir(μ‐Cl)}2] 2–6 and molecular structure of monomeric water oxidation catalyst 7 reported by Beller and coworkers.

Figure 13.3 Molecular structures of iridium complexes bearing sulfonamide ligands reported by Goldsmith, Bernhard, and coworkers.

Figure 13.4 Structure of [(cod)2ClIr2(μ‐bpi)] PF6 (17) catalyst and [(cod)Ir(Cl)(ppei)] (18) reported by de Bruin and coworkers.

Figure 13.5 Structures of [IrCl(Hedta)]Na+ (19) [36] and [Ir(2,6‐pyridinedicarboxylate)(1‐κ‐4,5‐η²‐C8H13)(MeOH)] (20) [37] reported by Macchioni and coworkers.

Figure 13.6 IrCp* WOCs [41, 47–53].

Figure 13.7 Dimer structures reported by Beller and coworkers (32) and Crabtree and coworkers (33).

Figure 13.8 CpIr WOCs reported by Crabtree and coworkers.

Figure 13.9 Derivatives of complex Cp*Ir(bpy)X and Cp*Ir(bpm)X [25, 49, 50].

Figure 13.10 Organometallic Ir complexes based on pyridinecarboxylate ligands reported by Macchioni and coworkers.

Figure 13.11 Structures of Cp*Ir complexes bearing normal carbene reported by Hetterscheid and Reek (47a–b)) and also investigated by Crabtree et al. (48a–d).

Figure 13.12 Structures of Cp*Ir(NHCMe,iPr)X2 (49) and a tethered version (50) reported by Lloret‐ Fillol and coworkers.

Figure 13.13 Structures of Cp*Ir(κ²C²,C² −NHC)Cl (51) reported by Crabtree and coworkers and Cp*Ir(κ²C²,C²−NHC(X)2Cl (52) reported by Macchioni and coworkers.

Figure 13.14 Ir–di‐NHC complexes reported by Crabtree and coworkers (53a and 54) and by Bonchio, Tubaro, and coworkers (53b and 55).

Figure 13.15 Structures of Cp*Ir WOCs bearing mesoionic C,Ntrz‐bidentate ligands reported by Bernhard, Albrecht, and coworkers.

Figure 13.16 Structures of Cp*Ir WOCs bearing chelating Npyr,Ctrz‐bidentate ligands reported by Bernhard, Albrecht, and coworkers.

Figure 13.17 Structures of Cp*Ir WOCs bearing mesoionic C,Ctrz‐bidentate ligands reported by Bernhard, Albrecht, and coworkers [20].

Figure 13.18 Structure of [Cp*Ir(trz)Cl2] (66) reported by Bernhard, Albrecht, and coworkers.

Figure 13.19 Structures of Cp*Ir complexes bearing a mesoionic Npyr,Ctrz‐bidentate carbene ligand reported by Macchioni, Albrecht, and coworkers.

Figure 13.20 Structures of Cp*Ir complexes bearing either a mesoionic imidazolylidene ligand (69) or a mesoionic triazolylidene (70) as reported by Bernhard, Albrecht, and coworkers.

Figure 13.21 Sketch of Ir(Hedta)Cl immobilized onto rutile TiO2 reported by Macchioni and coworkers.

Figure 13.22 Structures of high‐potential porphyrin 71 and WOC 22d that were co‐deposited on TiO2‐sintered fluorine‐doped tin oxide (FTO) electrode by Crabtree and coworkers.

Figure 13.23 Schematic representation of the immobilized [Cp*Ir(bpyL)(OH2)]²+ (L = PO3H or COOH) reported by Joya, de Groot, and coworkers.

Figure 13.24 Formation of the homobimetallic WOC‐74 and proposed molecular structure for the oxide‐adsorbed system as reported by Brudvig, Sheehan, and coworkers [79].

Figure 13.25 Representation of the proposed WOC molecular structure on a hematite surface reported by Brudvig, Wang, and coworkers.

Figure 13.26 Chemical structures of homogeneous catalysts incorporated into MOFs reported by Lin and coworkers.

Figure 13.27 Chemical structures of homogeneous catalysts incorporated into Zr–carboxylate MOF reported by Lin and coworkers.

Chapter 14

Figure 14.1 Molecular structures of iridium dyad 1–3 and model complex 4.

Figure 14.2 Absorption spectra of the dyads 1 (bold solid line), 2 (solid line), and 4 (dashed line).

Figure 14.3 Energy level diagram for 3.

Figure 14.4 Long dyad 5.

Figure 14.5 Molecular structure of iridium triad 6.

Figure 14.6 Energy level diagram in D–Ir(III)–A triad.

Figure 14.7 Iridium triad with the relevant two dyads and the reference complex.

Figure 14.8 Absorption (solid lines) and emission (dashed lines) spectra of the iridium triad and dyad complex.

Figure 14.9 Reference complex 7 and the D2–Ir dyad 8.

Figure 14.10 Absorption spectrum of 10 in MeCN. The green‐shaded region covers LC and MLCT excitations of the iridium complex, the red area π–π* excitations of the NDI, and the blue area mainly excitations of the TAA. The absorption spectrum of 9 is given as a violet solid line and the corresponding phosphorescence spectrum as a dashed violet line. The phosphorescence excitation spectrum of 9 is given as a green solid line.

Figure 14.11 Systematic structure of charged iridium complexes 11–13.

Figure 14.12 Current–voltage characteristics of DSC based on the iridium complexes 11 ( ), 12 ( ), and 13 ( ).

Figure 14.13 Molecular structures of cyclometalated iridium(III) complexes 14–18.

Figure 14.14 (a) Electronic absorption spectra of complexes 14 ( ), 15 ( ), 16 ( ), 17 ( ), and 18 ( ). (b) Photocurrent density–voltage (J–V) characteristic curves of DSCs sensitized with the same complexes.

Figure 14.15 Molecular structure of iridium complexes 19 and 20 and photocurrent–voltage curves for DSCs based on 19 ( ), 20 ( ), and 11 ( ).

Figure 14.16 Molecular structures of the iridium dyes 21–23.

Figure 14.17 (a) J–V characteristics of dyes 21 ( ), 22 ( ), and 23 ( ) sensitized solar cells TiO2 films under full sun. (b) Light‐harvesting efficiency (LHE) and absorbed photon‐to‐current conversion efficiency (APCE) based on 9 mm TiO2 films.

Figure 14.18 Sensitizers 24–27 based on iridium complexes with terdentate ligands.

Figure 14.19 (a) UV–Vis absorption (left)