Photophysical properties of trans-3-(4-monomethylamino-phenyl)-acrylonitrile: Evidence of twisted intramolecular charge transfer (TICT) process

A donor acceptor substituted aromatic system trans-3-(4-monomethylamino-phenyl)-acrylonitrile (MMAPA) has been synthesized and its photophysical behavior has been investigated in the solvent of different polarity by steady state absorption and emission, time-resolved emission and quantum chemical calculations. The observed dual fluorescence of MMAPA in polar aprotic solvents has been assigned to emission from the locally excited and twisted intramolecular charge transfer states. The low-energy emission in protic solvent is attributed to the hydrogen-bonded complex. Potential energy surfaces for the ground and excited states along the donor (-NHMe group) and acceptor (acrylonitrile group) twist coordinates have been calculated by time-dependent density functional theory (TDDFT) and time-dependent density functional theory-polarized continuum model (TDDFT-PCM) in the gas phase and in acetonitrile solvent, respectively. Calculations predict that the stabilized excited state along the twist coordinate is responsible for the solvent dependent red shifted charge transfer emission. It is found that the twisting along the donor site is energetically favorable compared to that of the acceptor site. The canonical crossing of the excited states for the twisting of the donor group and localized nitrogen lone pair orbital of -NHMe group at the perpendicular configuration with respect to p-orbitals of benzene ring support TICT model for photo-induced charge transfer reaction in MMAPA molecule.