Synthesis And Application Of The Ir(â…¢) Complexes And Re(â… )Complexes Showing Strong Absorption Of Visible Light

Iridium (Ⅲ) and Rhenium (Ⅰ) complexes have attracted much attention due to their tunable photophysical properties, ligand modification and applications in luminescent biological molecular probes, photovoltaics and photocatalysis, etc. Enhancing the absorption of visible light of these two complexes can increase the application in luminescent bioimaging, TTA upconversion and photooxidation, and so on. Therefore, how to improve the absorption of visible light for the Iridium (Ⅲ) and Rhenium (Ⅰ) complexes is the main task in this thesis.Recently we found that the visible light absorption and the triplet excited state lifetime of the complexes can be improved with the ligand modification.In this thesis, cyclometalated Ir(Ⅲ) complexes with pyrenyl fused imidazole CAN ligand and coumarin-fused bpy NN ligand were prepared. The target complex Ir-2shows strong absorption at466nm, which is20-fold that of the model complex Ir-0([Ir(ppy)2bpy][PF6], ppy=2-phenylpyridine, bpy=2,2’-bipyridine,λmax=405nm). At the same time, the triplet excited state lifetime of Ir-2was prolonged to73.9μs, which is246-fold that of Ir-0. With Ir-2as the triplet photosensitizers, TTA upconversion quantum yield of23.7%was observed.Next the Re(Ⅰ) complexes with different rigid imidazole ligands were studied. With the right chromophores, rhenium(I) tricarbonyl polypyridine complex shows strong absorption of visible light. The absorption of the target complex Re-1at473nm is12-fold that of the model complex Re-0([Re(CO)3Cl(PIP)], PIP=2-Phenyl-1H-Imidazo[4,5-f]-1,10-Phenanthroline, Amax=439nm) and the lifetime of the triplet excited state is86.0μs, which is39-fold that of Re-0. It is for the first time that Re(I) complexes were used as triplet photosensitizers for TTA based upconversion, and an upconversion quantum yield up to17.0%was observed.In order to prolong the absorption wavelength and enhance the absorption ability, ligands with BODIPY were introduced. Re-4(with Bodipy) and Re-5(with carbazole-ethynyl Bodipy) show unprecedented strong absorption of visible light at536nm and574nm, respectively. And this abilities of absorption are25-fold and18-fold that of the model complex Re-3([Re(CO)3Cl(bpy)],λmax=401nm), respectively. And the lifetime of Re-4and Re-5are4000and4892-fold that of Re-3. The complexes were used as triplet photosensitizers for1O2mediated photooxidation and TTA upconversion. With the strong visible light-harvesting ability, Re-4proved to be a twice better1O2photosensitizer than the conventional triplet photosensitizer tetraphenylporphyrin (TPP).The excited states were studied with nanosecond time-resolved transient absorption spectroscopy, emission at77K, excited state lifetime and theoretical calculations, et al. The complexes with strong absorption of visible light and long-lived triplet excited states are the very effective triplet photosensitizers for TTA upconversion and1O2mediated photooxidation. This study increases the choosing range of the triplet sensitizers for TTA based upconversion, and may also pave the way for application of the transition metal complexes as triplet photosensitizers in photocatalysis, photodynamic therapy (PDT), and so on.