Photophysics of Anionic Bis(4H-imidazolato)Cu(I) Complexes
in: Chemistry-A European Journal (2022)
In this paper,the photophysicalbehavior of four panchromatically absorbing, homoleptic bis(4H-imidazo-lato)Cu(I) complexes, with a systematic variation of the electron-withdrawing properties of theimidazolate ligand,werestud-iedby wavelength-dependent time-resolved femtosecond transient absorption spectroscopy. Excitation at400, 480, and 630nmpopulates metal-to-ligand charge-transfer, intra-ligand charge-transferas well as mixed charactersinglet states.The pumpwavelength-dependenttransient absorption data are analyzed by a recently established 2D correlation approach. The data analysis reveals that all excitation conditions yield similar excited state dynamics. Key to the excited-state relaxation is fast,subpicosecond pseudo-Jahn-Teller distortion,which is accompaniedby re-localization of electron densityonto a single ligand from the initially delocalized state atFranck-Condon geometry.The subsequent intersystem crossing to the triplet manifold is followed by a sub-100ps decay to the ground state. The fast,non-radiative decay is rationalized by the low triplet state energy as found by DFT calculations, which suggest the perspective treatment in the strong coupling limit of the energy gap law.