An AIE Metal Iridium Complex: Photophysical Properties and Singlet Oxygen Generation Capacity

Photodynamic therapy (PDT) has garnered significant attention in the fields of cancer treatment and drug-resistant bacteria eradication due to its non-invasive nature and spatiotemporal controllability. Iridium complexes have captivated researchers owing to their tunable structure, exceptional optical properties, and substantial Stokes displacement. However, most of these complexes suffer from aggregation-induced quenching, leading to diminished luminous efficiency. In contrast to conventional photosensitizers, photosensitizers exhibiting aggregation-induced luminescence (AIE) properties retain the ability to generate a large number of reactive oxygen species when aggregated. To overcome these limitations, we designed and synthesized a novel iridium complex named Ir-TPA in this study. It incorporates quinoline triphenylamine cyclomethylated ligands that confer AIE characteristics for Ir-TPA. We systematically investigated the photophysical properties, AIE behavior, spectral features, and reactive oxygen generation capacity of Ir-TPA. The results demonstrate that Ir-TPA exhibits excellent optical properties with pronounced AIE phenomenon and robust capability for producing singlet oxygen species. This work not only introduces a new class of metal iridium complex photosensitizer with AIE attributes but also holds promise for achieving remarkable photodynamic therapeutic effects in future cellular experiments and biological studies.


Introduction
Photodynamic therapy is a selective process in which photosensitizer molecules absorb the appropriate wavelength of light and initiate the photoactivation process to produce toxic substances, thus leading to apoptosis or necrosis of pathological tissue cells [1,2].Photodynamic therapy (PDT) has attracted extensive attention from researchers due to its advantages such as non-invasive, spatiotemporal controllability, and not easy to induce drug resistance [3][4][5].The mechanism of photodynamic therapy is that under the corresponding wavelength of light, the photosensitizer in the ground state absorbs energy, transitions from the ground state to the single excited state, and then reaches the triple excited state through intersystem transition (ISC).The photosensitizer in the triple excited state returns to the ground state in two ways, corresponding to Type I and Type II photodynamic therapy processes, respectively [6].In the process of Type I photodynamic therapy, photosensitizers in the triple excited state first undergo electron transfer with surrounding molecules to generate free radicals, and then interact with oxygen-containing substrates to produce reactive oxygen species such as hydroxyl free radicals (OH•), superoxide free radicals (O 2 • − ), and hydrogen peroxide (H 2 O 2 ), causing oxidative damage to cells [7].
Molecules 2023, 28, 7914 2 of 12 In the process of type II photodynamic therapy, the photosensitizer in the triple excited state transfers energy to oxygen molecules in the process of returning to the ground state, forming singlet oxygen ( 1 O 2 ).Singlet oxygen has strong activity and can interact with numerous biological substrates to induce cell oxidation and then kill, thus achieving the purpose of photodynamic therapy [8,9]. 1 O 2 generated by Type II light reaction can oxidize major biomolecules of the nuclear membrane and cell membrane, such as unsaturated lipids and amino acids of proteins, and cause cell apoptosis, so 1 O 2 is toxic [10].
Although PDT possesses the aforementioned advantages, achieving enhanced clinical efficacy remains a significant challenge.In this regard, the precise selection and design of photosensitizers play a crucial role in determining the therapeutic outcomes of PDT [11].The ability of traditional organic small molecules to transduce between systems has great limitations.Iridium's large atomic number enables strong spin-orbit coupling, which is conducive to phosphor emission [12].The excited states of iridium complexes are characterized not only by MLCT, but also by ligand-to-ligand charge transfer (LLCT) and in vivo charge transfer (ILCT) [13].Iridium complexes, compared to other transition metal complexes, exhibit excellent photochemical and physical stability, large Stokes shift, and high intersystem crossover ability [14].Consequently, they have emerged as extensively utilized transition metal complex materials across various domains such as bioimaging, electroluminescence, and photodynamic therapy [15][16][17][18][19]. Notably, iridium complexes have been extensively investigated as photosensitizers in photodynamic therapy [20,21].For instance, we successfully synthesized UCNPs@Ir-2-N-a near-infrared absorbing photosensitizerby combining an AIE iridium complex with upconversion nanoparticles (UCNPs).This study demonstrates the promising application potential of metal iridium complex PSs in PDT [22].
Traditional small molecule photosensitizers, such as porphyrins [23], usually have large planar conjugated structures and strong intermolecular π-π accumulation, and their luminous intensity will gradually weaken and even quench when they are aggregated, a phenomenon called Aggregation-caused Quenching (ACQ) [24].This Aggregationcaused Quenching (ACQ) phenomenon significantly reduces their photosensitization ability, severely limiting their practical application [25,26].In addition, the fluorescence emitted by conventional photosensitizers is usually non-luminous, resulting in reduced imaging sensitivity [27,28] and placing great limitations on the clinical application of many photosensitizers in photodynamic therapy (PDT).In 2001, academician Tang's research group found the opposite phenomenon to ACQ: under dilute solution conditions, these photosensitizers emit weak or even no light, but with the increase in concentration, the luminescence is significantly enhanced [29].Unlike ACQ photosensitizers, photosensitizers with Aggregation-induced Emission (AIE) properties typically have a non-planar structure.The intramolecular motion in the aggregation state is limited; thus, the rigidity of the molecular structure is increased, the non-radiative attenuation pathway is reduced, and, finally, the radiative attenuation pathway dominates.Limited intramolecular motion reduces non-radiative energy dissipation while enhancing fluorescence emission and sensitizing a large number of reactive oxygen species (ROS) in the aggregation state, thus providing a huge advantage for image-guided PDT [30][31][32].However, there are few examples of iridium complexes with AIE properties used in photodynamic therapy.Therefore, the development of iridium-based AIE active photosensitizers is of great significance to promote the application of PDT.
In this study, we developed and synthesized an iridium complex called Ir-TPA by incorporating a quinoline triphenylamine ligand.We conducted comprehensive investigations on the photophysical properties, AIE characteristics, spectral properties, and singlet oxygen generation capacity of Ir-TPA.As shown in Scheme 1, our findings demonstrate that Ir-TPA exhibits excellent optical properties, displays remarkable AIE behavior, and possesses strong capability in generating reactive oxygen species.This research confirms the significant potential of AIE properties in enhancing the effectiveness of photodynamic therapy and presents a fresh perspective on utilizing iridium complexes in the field of photodynamic therapy.
Molecules 2023, 28, x FOR PEER REVIEW 3 of 12 and possesses strong capability in generating reactive oxygen species.This research confirms the significant potential of AIE properties in enhancing the effectiveness of photodynamic therapy and presents a fresh perspective on utilizing iridium complexes in the field of photodynamic therapy.

Analysis of Photophysical Properties of Complexes
The photophysical properties of Ir-TPA and Ir-py were analyzed by ultraviolet absorption and fluorescence emission spectra.As shown in Figure 1, similar to the iridium complexes reported in the literature, Ir-TPA has two characteristic absorption peaks in a certain wavelength range.There is a strong characteristic absorption peak in the wavelength range of 250~350 nm, which is caused by the central charge ( 1 LC, π-π*) transition of the ligand in the metal iridium complex.There is a weak absorption band in the 350 nm to visible light band, which can be attributed to metal-ligand charge transfer transition (MLCT) and ligand-ligand charge transfer (LLCT) of the metal iridium complex [33].It can be clearly seen from the figure that the molar absorption coefficient of Ir-TPA was significantly enhanced compared with Ir-py after the introduction of the quinoline triphenylamine ligand (Table 1).Especially in the 425 nm visible region, the molar coefficient of Ir-TPA is 41,680 m −1 cm −1 , which is eight times that of Ir-py.It can be shown that the absorption peak of the iridium complex is obviously enhanced after the introduction of the quinoline triphenylamine ligand.Subsequently, we determined the photoluminescent quantum yields (PLQYs) and excited state lifetimes of Ir-TPA and Ir-py at CH3CN/H2O (v/v = 1/9) and summarized the corresponding photophysical data in Table 1.It can be seen from the data in the table that Ir-TPA and Ir-py have good photophysical properties.

Analysis of Photophysical Properties of Complexes
The photophysical properties of Ir-TPA and Ir-py were analyzed by ultraviolet absorption and fluorescence emission spectra.As shown in Figure 1, similar to the iridium complexes reported in the literature, Ir-TPA has two characteristic absorption peaks in a certain wavelength range.There is a strong characteristic absorption peak in the wavelength range of 250~350 nm, which is caused by the central charge ( 1 LC, π-π*) transition of the ligand in the metal iridium complex.There is a weak absorption band in the 350 nm to visible light band, which can be attributed to metal-ligand charge transfer transition (MLCT) and ligand-ligand charge transfer (LLCT) of the metal iridium complex [33].It can be clearly seen from the figure that the molar absorption coefficient of Ir-TPA was significantly enhanced compared with Ir-py after the introduction of the quinoline triphenylamine ligand (Table 1).Especially in the 425 nm visible region, the molar coefficient of Ir-TPA is 41,680 m −1 cm −1 , which is eight times that of Ir-py.It can be shown that the absorption peak of the iridium complex is obviously enhanced after the introduction of the quinoline triphenylamine ligand.Subsequently, we determined the photoluminescent quantum yields (PLQYs) and excited state lifetimes of Ir-TPA and Ir-py at CH 3 CN/H 2 O (v/v = 1/9) and summarized the corresponding photophysical data in Table 1.It can be seen from the data in the table that Ir-TPA and Ir-py have good photophysical properties.  1 Determined at CH3CN/H2O (v/v = 1/9) with a concentration of 1.0 × 10 −5 M, λex = 467 nm. 2 Determined at CH3CN/H2O (v/v = 1/9) with a concentration of 1.0 × 10 −5 M, λex = 395 nm.

Analysis of AIE Properties of Complexes
The AIE properties of Ir-TPA and Ir-py were analyzed in CH3CN and water mixed system solution (water content ranged from 0 to 90%).As shown in Figure 2, Ir-py exhibited weak emission in pure CH3CN solution, but with the increase in water content, the luminescence gradually weakened, showing obvious aggregation-induced quenching phenomenon.Iridium complex Ir-TPA was obtained by using quinoline triphenylamine derivatives as cyclometalated ligands, which basically did not emit light in pure CH3CN.The luminescence of Ir-TPA increased gradually with the increase in the water content of the bad solvent.When the water content of the mixed solution reaches 80%, Ir-TPA emits bright red light, and Ir-TPA has typical AIE characteristics.

Analysis of AIE Properties of Complexes
The AIE properties of Ir-TPA and Ir-py were analyzed in CH3CN and water mixed system solution (water content ranged from 0 to 90%).As shown in Figure 2, Ir-py exhibited weak emission in pure CH3CN solution, but with the increase in water content, the luminescence gradually weakened, showing obvious aggregation-induced quenching phenomenon.Iridium complex Ir-TPA was obtained by using quinoline triphenylamine derivatives as cyclometalated ligands, which basically did not emit light in pure CH3CN.The luminescence of Ir-TPA increased gradually with the increase in the water content of the bad solvent.When the water content of the mixed solution reaches 80%, Ir-TPA emits bright red light, and Ir-TPA has typical AIE characteristics.

Analysis of AIE Properties of Complexes
The AIE properties of Ir-TPA and Ir-py were analyzed in CH 3 CN and water mixed system solution (water content ranged from 0 to 90%).As shown in Figure 2, Ir-py exhibited weak emission in pure CH 3 CN solution, but with the increase in water content, the luminescence gradually weakened, showing obvious aggregation-induced quenching phenomenon.Iridium complex Ir-TPA was obtained by using quinoline triphenylamine derivatives as cyclometalated ligands, which basically did not emit light in pure CH 3 CN.The luminescence of Ir-TPA increased gradually with the increase in the water content of the bad solvent.When the water content of the mixed solution reaches 80%, Ir-TPA emits bright red light, and Ir-TPA has typical AIE characteristics.
Ir-TPA showed more emission redshift than Ir-py due to the better conjugation of cyclometal ligands derived from quinoline triphenylamine.Ir-TPA exhibits excellent red light emission and larger Stokes shifts value, indicating that in future biological experiments, autofluorescence interference will be effectively avoided, and the signal-to-noise ratio of imaging will be improved, which has a broad prospect in future biological applications.
Then, we further investigated the AIE phenomena of Ir-TPA by UV-Vis absorption spectra.As can be seen from Figure 3, with the gradual increase in water content in the system, the tail of the absorption spectrum slightly warped, indicating that the Mi scattering phenomenon occurred [34].
As shown in Figure 4, we further used dynamic light scattering (DLS) to analyze the hydrated particle size of Ir-TPA in CH 3 CN/H 2 O (v/v = 1/9) and CH 3 CN solutions, respectively, to prove that Ir-TPA will aggregate when the proportion of poor solvent water increases.DLS showed that the average hydration kinetic radius of Ir-TPA at 0% (CH 3 CN solution) and 90% (CH 3 CN/H 2 O = 1/9) water content was 15.33 nm and 66.27 nm, respectively.The average hydration kinetic radius of Ir-TPA is more than four times that of the dispersion state when the content of the poor solvent water reaches 90%.Therefore, it can be well explained that Ir-TPA does occur as an aggregation phenomenon.Through the above experimental results, we can conclude that the complex Ir-TPA has good AIE performance, which is due to the emission enhancement caused by aggregation in poor solvents.
luminescence gradually weakened, showing obvious aggregation-induced quenching phenomenon.Iridium complex Ir-TPA was obtained by using quinoline triphenylamine derivatives as cyclometalated ligands, which basically did not emit light in pure CH3CN.The luminescence of Ir-TPA increased gradually with the increase in the water content of the bad solvent.When the water content of the mixed solution reaches 80%, Ir-TPA emits bright red light, and Ir-TPA has typical AIE characteristics.Ir-TPA showed more emission redshift than Ir-py due to the better conjugation of cyclometal ligands derived from quinoline triphenylamine.Ir-TPA exhibits excellent red light emission and larger Stokes shifts value, indicating that in future biological experiments, autofluorescence interference will be effectively avoided, and the signal-to-noise ratio of imaging will be improved, which has a broad prospect in future biological applications.
Then, we further investigated the AIE phenomena of Ir-TPA by UV-Vis absorption spectra.As can be seen from Figure 3, with the gradual increase in water content in the system, the tail of the absorption spectrum slightly warped, indicating that the Mi scattering phenomenon occurred [34].Ir-TPA showed more emission redshift than Ir-py due to the better conjugation of cyclometal ligands derived from quinoline triphenylamine.Ir-TPA exhibits excellent red light emission and larger Stokes shifts value, indicating that in future biological experiments, autofluorescence interference will be effectively avoided, and the signal-to-noise ratio of imaging will be improved, which has a broad prospect in future biological applications.
Then, we further investigated the AIE phenomena of Ir-TPA by UV-Vis absorption spectra.As can be seen from Figure 3, with the gradual increase in water content in the system, the tail of the absorption spectrum slightly warped, indicating that the Mi scattering phenomenon occurred [34].As shown in Figure 4, we further used dynamic light scattering (DLS) to analyze the hydrated particle size of Ir-TPA in CH3CN/H2O (v/v = 1/9) and CH3CN solutions, respectively, to prove that Ir-TPA will aggregate when the proportion of poor solvent water increases.DLS showed that the average hydration kinetic radius of Ir-TPA at 0% (CH3CN tively.The average hydration kinetic radius of Ir-TPA is more than four times that of the dispersion state when the content of the poor solvent water reaches 90%.Therefore, it can be well explained that Ir-TPA does occur as an aggregation phenomenon.Through the above experimental results, we can conclude that the complex Ir-TPA has good AIE performance, which is due to the emission enhancement caused by aggregation in poor solvents. (a) (b)

Analysis of Singlet Oxygen Generation Capacity in Solution
The ability of photosensitizer to produce singlet oxygen is very important for the effect of photodynamic therapy.The singlet oxygen production capacity of two iridium complexes Ir-TPA and Ir-py at CH3CN:H2O (V:V = 1:9) was evaluated by monitoring the absorbance change of ABDA at 380 nm using ABDA as an indicator.As shown in Figures 5-7, for (1) the light group containing PSs; (2) the unilluminated group containing PSs and ABDA; and (3) for the ABDA light group alone, the absorption intensity basically did not change during the time of illumination 360 s, which proves that Ir-TPA and Ir-py have good light stability.As shown in Figure 8, when irradiated with a white LED lamp, the absorption of Ir-TPA and Ir-py at 380 nm is significantly reduced, which proves the production of singlet oxygen under the illumination condition.As shown in Figure 9, the singlet oxygen generation capacity of Ir-TPA and Ir-py both conform to the first-order kinetic equation.The higher the slope, the stronger the singlet oxygen generation capacity, and the singlet oxygen generation efficiency is Ir-TPA > Methylene Blue (MB) > Ir-py.As shown in Table 2, using methylene blue as the reference, the 1 O2 quantum yield of Ir-TPA is as high as 83.5%, indicating that Ir-TPA can efficiently produce singlet oxygen, and they will play an important role in the application of PDT cancer as Ps.

Analysis of Singlet Oxygen Generation Capacity in Solution
The ability of photosensitizer to produce singlet oxygen is very important for the effect of photodynamic therapy.The singlet oxygen production capacity of two iridium complexes Ir-TPA and Ir-py at CH 3 CN:H 2 O (V:V = 1:9) was evaluated by monitoring the absorbance change of ABDA at 380 nm using ABDA as an indicator.As shown in Figures 5-7, for (1) the light group containing PSs; (2) the unilluminated group containing PSs and ABDA; and (3) for the ABDA light group alone, the absorption intensity basically did not change during the time of illumination 360 s, which proves that Ir-TPA and Ir-py have good light stability.As shown in Figure 8, when irradiated with a white LED lamp, the absorption of Ir-TPA and Ir-py at 380 nm is significantly reduced, which proves the production of singlet oxygen under the illumination condition.As shown in Figure 9, the singlet oxygen generation capacity of Ir-TPA and Ir-py both conform to the first-order kinetic equation.The higher the slope, the stronger the singlet oxygen generation capacity, and the singlet oxygen generation efficiency is Ir-TPA > Methylene Blue (MB) > Ir-py.As shown in Table 2, using methylene blue as the reference, the 1 O 2 quantum yield of Ir-TPA is as high as 83.5%, indicating that Ir-TPA can efficiently produce singlet oxygen, and they will play an important role in the application of PDT cancer as Ps.

General Information
Reagents and solvents should be used as received from the supplier.Unless otherwise specified, all purification is performed using 200-300 mesh silica gel from the supplier by column chromatography.The structure was confirmed by Bruker AV600 NMR spectrometer (Bruker, Billerica, MA, USA) and Bruker autoFlex III mass spectrometer (Bruker, Billerica, MA, USA).A Shimadzu UV-3100 spectrophotometer (Shimadzu, Kyoto, Japan) was used for ultraviolet-visible experiments.The fluorescence emission spectra were measured by Edinburgh FLS920 steady-state transient fluorescence spectrometer (Edinburgh Instruments Ltd., Livingston, UK).Dynamic light scattering (DLS) was tested using NanoZS90.

Solution Preparation Method
The spare solution of Ir-TPA and Ir-py (1 mM) was prepared in acetonitrile.The preparation method of the test solution was as follows: during the test, 30 µL Ir-TPA and

General Information
Reagents and solvents should be used as received from the supplier.Unless otherwise specified, all purification is performed using 200-300 mesh silica gel from the supplier by column chromatography.The structure was confirmed by Bruker AV600 NMR spectrometer (Bruker, Billerica, MA, USA) and Bruker autoFlex III mass spectrometer (Bruker, Billerica, MA, USA).A Shimadzu UV-3100 spectrophotometer (Shimadzu, Kyoto, Japan) was used for ultraviolet-visible experiments.The fluorescence emission spectra were measured by Edinburgh FLS920 steady-state transient fluorescence spectrometer (Edinburgh Instruments Ltd., Livingston, UK).Dynamic light scattering (DLS) was tested using NanoZS90.

Solution Preparation Method
The spare solution of Ir-TPA and Ir-py (1 mM) was prepared in acetonitrile.The preparation method of the test solution was as follows: during the test, 30 µL Ir-TPA and Ir-py reserve solution, 270 µL acetonitrile, and 2700 µL ultra-pure water were prepared into the test solution with a total volume of 3 mL.

Fluorescent Spectrum Test Method
The steady-state spectra PL and phosphor decay lifetime under photoluminescence were measured by an Edinburgh FLS920 steady-state transient fluorescence spectrometer, and the quantum yield ΦPL was measured by integrating a sphere with acetonitrile/water (v/v = 1/9) as the basis.A 450 W xenon lamp is used as the light source when measuring the attenuation life of the spectrum.

Test Method for Singlet Oxygen in Solution
The efficacy of photodynamic therapy is evaluated by the level of singlet oxygen production in the solution.The 1 O 2 formation capacity of Ir-TPA/Ir-py at CH 3 CN/H 2 O = 1/9 was evaluated using 9, 10-anthracenedi-bis (methylene) dicarboxylic acid (ABDA) as an indicator.After a certain time of light irradiation, the absorbance of ABDA at 380 nm was significantly reduced, indicating that the photosensitizer sensitized oxygen to produce 1 O 2 .In this experiment, CH 3 CN/H 2 O = 1/9 solution containing Ir-TPA/Ir-py (25 µM) was prepared and mixed with ABDA (30 µg•mL −1 ), and then exposed to white light (400-700 nm, 20 mW cm −2 ) for irradiation.The absorption intensity of ABDA at 380 nm was monitored every 60 s.

Synthesis and Characterization of Complexes
The resultant route is detailed in Figure 10.
and the quantum yield ΦPL was measured by integrating a sphere with acetonitrile/water (v/v = 1/9) as the basis.A 450 W xenon lamp is used as the light source when measuring the attenuation life of the spectrum.

Test Method for Singlet Oxygen in Solution
The efficacy of photodynamic therapy is evaluated by the level of singlet oxygen production in the solution.The 1 O2 formation capacity of Ir-TPA/Ir-py at CH3CN/H2O = 1/9 was evaluated using 9, 10-anthracenedi-bis (methylene) dicarboxylic acid (ABDA) as an indicator.After a certain time of light irradiation, the absorbance of ABDA at 380 nm was significantly reduced, indicating that the photosensitizer sensitized oxygen to produce 1 O2.In this experiment, CH3CN/H2O = 1/9 solution containing Ir-TPA/Ir-py (25 µM) was prepared and mixed with ABDA (30 µg•mL −1 ), and then exposed to white light (400-700 nm, 20 mW cm −2 ) for irradiation.The absorption intensity of ABDA at 380 nm was monitored every 60 s.

Synthesis and Characterization of Complexes
The resultant route is detailed in Figure 10.3.5.1.Synthesis of Cyclometalated Ligand TPA Trianiline 4-borate (0.972 g, 3.36 mmol) and 1-chloroisoquinoline (0.496 g, 3.06 mmol) were dissolved in 30 mL toluene, and the catalyst tetrtriphenylphosphine palladium (0.177 g, 0.15 mmol) and 2 mol/L sodium carbonate solution 20 mL were added.The reaction was kept at 110 °C for 48 h in a deoxygenated environment.After the reaction, the organic phase was extracted and dried with anhydrous magnesium sulfate, filtered, and purified 3.5.1.Synthesis of Cyclometalated Ligand TPA Trianiline 4-borate (0.972 g, 3.36 mmol) and 1-chloroisoquinoline (0.496 g, 3.06 mmol) were dissolved in 30 mL toluene, and the catalyst tetrtriphenylphosphine palladium (0.177 g, 0.15 mmol) and 2 mol/L sodium carbonate solution 20 mL were added.The reaction was kept at 110 • C for 48 h in a deoxygenated environment.After the reaction, the organic phase was extracted and dried with anhydrous magnesium sulfate, filtered, and purified by silica gel column chromatography (dichloromethane/petroleum ether, 10/5).The product is a light yellow solid with a yield of 68%.

Synthesis of L1
TPA (0.930 g, 2.5 mmol) and IrCl 3 •3H 2 O (0.317 g, 1 mmol) were dissolved in a mixed solution of 30 mL ethylene glycol ether and 10 mL water, and the reaction was continued for 24 h at 120 • C under nitrogen atmosphere.At the end of the reaction, water was added to the round-bottom flask and continued to stir for 30 min.The Brinell funnel was used for pumping and filtering, and the obtained solids were put into the oven for 24 h.After drying, the product became a deep red solid with a yield of 80%.The product is directly used in subsequent reactions.

Scheme 1 .
Scheme 1. Structure of Ir-TPA and schematic diagram of Ir-TPA producing singlet oxygen.* Represents an excited state and the checkmark indicates that the work is a Type II photodynamic process.

Scheme 1 .
Scheme 1. Structure of Ir-TPA and schematic diagram of Ir-TPA producing singlet oxygen.* Represents an excited state and the checkmark indicates that the work is a Type II photodynamic process.

Table 1 .
Photophysical data of Ir

Table 2 .
Singlet oxygen generation efficiency data of

Table 2 .
Singlet oxygen generation efficiency data of Ir