Time-resolved spectroscopy study of the triplet state of 4-diethylaminobenzonitrile (DEABN)

Abstract

The nonradiative deactivation processes of intramolecular charge transfer (ICT) and intersystem crossing (ISC) and their dependence on solvent polarity for DEABN have been studied using transient absorption (TA) spectroscopy. The TA spectra have been taken in non-polar hexane and polar acetonitrile solvents within the 400–630 nm spectral region at time delays of 2 ps to 6 ns. The results are complemented by nanosecond time-resolved resonance Raman (TR³) spectra of the triplet state of DEABN over the 700 to 2300 cm⁻¹ frequency range. There is no significant difference between the Raman spectra recorded in hexane, acetonitrile and methanol solvents and this implies the triplet state has only one form. Comparison of DEABN triplet Raman spectrum with ab initio DFT geometry and vibrational analysis of DEABN ground state and triplet state TR³ spectra of the closely related compound dimethylaminobenzonitrile (DMABN) indicates the DEABN triplet state is planar or near planar in structure with noticeable biradical character.