Can the dipolarity of the medium induce the formation of charge transfer structures? An unexpected finding in the photophysics of DMABN.

A thorough analysis of the absorption and emission spectra of p-dimethylaminobenzonitrile (DMABN) in ethyl acetate, diethyl ether, 1-chlorobutane, dichloromethane and trimethyl phosphate recorded at both 298 K and the melting point of each solvent allowed us to examine the corresponding emission excitation spectra by monitoring light across the dual fluorescence emission for DMABN. Based on its excitation spectra, DMABN forms charge transfer structures in solvents with a dipolarity exceeding 0.9 on the SdP (solvent dipolarity) scale that can be directly excited to a TICT structure from their ground electronic state. These results contradict the widespread assumptions made about the photophysics of DMABN over the past fifty years.