Excited state dynamics of Cu(I) photosensitisers with ultrafast X-ray spectroscopy Rory Cowin 1 , M V Appleby 1 , I Ivalo 1 , K E Royle 1 , J A Weinstein 1 , F Lima 2 , D. Khakhulin 2 , M Biednov 2 , Y Uemura 2 1 University of Sheffield, UK, 2 European XFEL GmbH, Germany Heteroleptic Cu(I) complexes employing bulky, sterically hindering ligands can extend the lifetime of the excited MLCT state by inhibiting the excited state distortion. The nano-to-microsecond excited state lifetimes of these compelxes makes them effective antibacterial agents, through generation of singlet oxygen. We have studied the photophysical properties of a series of Cu(I) xantphos diimine complexes, though transient optical absoprtion (TA), flourescence up-conversion and transient X-ray absorption and emission spectroscopy (XAS & XES), supported by TDDFT calculations. These complimentary techniques show that the heteroleptic Cu(I) complexes have arrays of excited states similar to those of the more well studied homoleptic Cu(I) diimines, but differ significantly in dynamics. The long lived and singlet oxygen generating T1 excited state is believed to be rapidly populated by ultrafast intersystem crossing (<; 100 fs), before being depopulated by several competing mechanisms. including by excited state distortion and reverse intersystem crossing. References
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