Excited State Dynamics in Dinuclear {Cu2(u-I)2} Complexes Bearing Ar-BIAN Ligands

Dynamics of the exited state of three complexes C1, C2 and C3 in dichloromethane have been probed by Transient Absorption Spectroscopy in the femtosecond time domain at different excitation wavelengths. The three complexes, regardless to the substitution pattern of corresponding free ligands (Figure I), revealed almost identical photophysical behaviour. In all case the excited complexes from an initially 1(M+X)LCT state either relax to the ground state or undergo fast Intersystem Crossing to 3(M+X)LCT within ~1 ps. In these dimeric systems the radiationless relaxation from 3(M+X)LCT occurs within the very fast time constant of ~25 ps. This unusual fast spin forbidden deactivation can be explained by Energy Gap Law through nested Potential Energy Sutrfaces of T1 and S0. When samples were excited at higher energies (440 nm) some photodegredation with ligand dissociation was observed. Despite of similar photophysical behaviour the extent of photodegredation is significantly reduced by introduction of NO2 group in acenaphthene moiety of the free ligands. This functionalization made us possible to study the deactivation dynamics of the excited states in halide-bridged dimeric Cu(I) complexes bearing Ar-BIAN ligands.