Intramolecular charge transfer in di-tert-butylaminobenzonitriles and 2,4,6-tricyanoanilines: A computational TDDFT study

The time-dependent DFT calculations for the low-lying excited electronic states of 4- and 3-di-tert-butylaminobenzonitrile, and 2,4,6-tricyano-N,N-dimethylaniline and 2,4,6-tricyanoaniline have been performed to investigate the mechanism of photo-induced intramolecular charge transfer (ICT). In addition, CC2-RI calculations were performed for TCDMA. For di-tert-butylaminobenzonitriles, we found evidence for the π σ ∗ -state mediated mechanism associated with the sequential state-switches: π π ∗ → π σ ∗ → ICT . It is predicted that 2,4,6-tricyano-N,N-dimethylaniline (TCDMA), but not 2,4,6-tricyanoaniline, possesses two ICT states, one of which shows the ICT-characterized quinoidal geometry and lies below the initially photo-excited S 1 ( π π ∗ ) state. The π π ∗ → ICT formation in TCDMA feasibly occurs in accord with the observed time-resolved excited-state absorption spectra and the biexponential fluorescence decay from the mixed S 1 ( π π ∗ ) /ICT state of TCDMA.