| Pt(II) complexes with intense visible light absorption and long lived triplet lifetimes have been applied in photocatalysis, oxygen sensing and triplet-triplet annihilation (TTA) upconversion based on electron or energy transfer. Coventional Pt(II) complexes show weak absorption of visible light with the molar absorption coefficents smaller than10000M-1cm-1, as well as the lifetimes of triplet states shorter than5μs. They are not good sensitizers for TTA upconversion. Recently some platinum complexes have been applied in TTA upconvertion such as Pt(Ⅱ) bisacetylide complexes, cyclometalated Pt(Ⅱ) complexes and bis (alkylphosphine) platinum(Ⅱ)-alkynyl complexes. Much room is left to explore new Pt(Ⅱ) complexes with broadband absorption, easily tuned structures and triplet state’s photophysical properties.The ligands were attached to the coordination Pt(Ⅱ) center through conjugation bonds to improve the efficiency of ISC, with the heavy atom effect maximum. It can lead to intense absorption of visible light and is called direct metalation. On the other hand, the1IL energy level of the ligands should be slightly higher than that of1MLCT for the complexes, whereas the3IL energy level of the ligands should be lower than that of3MLCT to gain long-lived3IL state. Last not least, complexes with broadband absorption band in visible region can harvest more broadband photoexcitation energy such as solar light which is beneficial to TTA upconvertion.Some visible light-harvesting Pt(Ⅱ) complexes were synthesized according to the above rationales and applied in TTA upconvertion, such as regioisomer N∧NPt(Ⅱ) bisacetylide complexes, symmetric and asymmetric linear trans-bis(tributylphosphine) Pt(Ⅱ) bis(acetylide) complexes with coumarin, naphthalimide and phenyl acetylides ligands and heteroleptic trans bis(alkylphosphine) platinum(Ⅱ)-alkynyl complexes with Bodipy and naphthalenediimide ligands showing strong absorption of visible light as well as long triplet state lifetimes. The photophysical properties for the Pt(Ⅱ) complexes were studied according to the ateady-state, time-resolved,77K spectra and DFT calculations.1. N∧N Pt(Ⅱ) Bis(acetylide) complexes Pt-1and Pt-2with regioisomeric amino naphthalenedimide acetylide ligands show strong visible light absorption and distinctly different photophysical properties, such as maximum absorbtion wavelength (485nm vs.465 nm), molar absorption coefficents (29200M-1cm-1vs.14300M-1cm-1), triplet excited states lifetimes (23.7μs vs.0.9μs) and TTA upconvertion quantum yields (15.0%vs.1.1%).2. A series of symmetric and unsymetric trans bis(alkylphosphine) Pt(II) bisacetylide complexes with functionalized aryl alkynyl ligands (coumarin, naphthalimide and phenyl acetylides) were prepared, showing intense visible light (421-459nm,ε=20900-76800M-1cm-1) as well as long-lived triplet state(16.0μs-139.9μs). The complexes were applied in TTA upconvertion with DPA and perylene as the acceptors and upconvertion quantum yield upto27.2%. Pt-7showing fluorescence/phosphorescence dual emission. was applied in O2sensing with high sensitivity.3. Broadband visible light-absorbing (400nm-650nm) trans bis(alkylphosphine) platinum(II)-alkynyl complexes Pt-9with resonance energy transfer (RET) between meso-(4’-ethylpehnyl) Bodipy and2-amino-4-ethyl naphthalenediimide ligands was prepared. There is intramolecular singlet and triplet energy transfer as well as triplet equilibrium in Pt-9whose triplet state is more localized on NDI moiety with lifetime determined as36.9μs. When applied in TTA upconvertion, upconversion quantum yield upto18.4%was observed for Pt-9. |
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