Effect of Back Skeleton Ligand on Ultrafast Excited-state Dynamics of Cu(I) Cyano Substituted Bipyridine Complexes

Abstract

Cu(I) complexes have attracted a lot of research interest for their potential replacement of functional noble metal complexes. In previous researches of Cu(I) complexes’ ultrafast dynamics, most of the acceptor ligands used are symmetric and only a limited number of asymmetric ligands examples were reported. To further understanding the ultrafast excited states’ dynamics of Cu(I) complexes with asymmetric cyano-substituted bipyridine electron acceptors ligand, Cu(I) complexes with 6-cyano-2,2ʹ-bipyridine and 4,4ʹ-dimethyl-6-cyano-2,2ʹ-bipyridine ligand in dichloromethane and acetonitrile were investigated by applying femtosecond time-resolved transient absorption (TA) spectroscopy. From the TA spectra, it was found that there are two different metal-to-ligand charge transfer (MLCT) states with different nature could be populated after pseudo-Jahn-Teller distortion. Time-dependent density functional theory (TD-DFT) calculation results also support this hypothesis that in one MLCT state, electron density is donated from Cu(I) center to the cyanobipyridine ligand with electron density delocalised on the whole bipyridine ligand and in the other MLCT state is with electron density donated from Cu(I) center to the cyano-substituted pyridine fragment of the cyanobipyridine ligand. This result indicates that asymmetric electron acceptors may lead to extra excited states could be populated comparing with symmetric electron acceptors.