REACTION DYNAMICS OF CHARGE-TRANSFER STATE FORMATION OF 4-(N,N-DIMETHYLAMINO)BENZONITRILE IN A METHANOL SOLUTION - THEORETICAL ANALYSES

The reaction dynamics of twisted intramolecular charge-transfer (TICT) state formation of 4-(N,N-dimethylamino)benzonitrile (DMABN) in methanol solvent has been studied theoretically. Molecular dynamics calculations were carried out for the St state of DMABN, and the reaction free energy surfaces were constructed as a function of solvation coordinate and torsional angle of the dimethylamino group. The solvation coordinate was defined by the potential energy difference between the S-1 and S-2 states. It was found that the potential barrier for the TICT state formation exists and the free energy along the solvation coordinate was well represented by the harmonic curves, To investigate the dynamics of reaction, the equations of motions for the solvation coordinate and the torsional angle were derived and stochastic trajectory calculations were carried out. The results were that (a) the reaction rate is significantly slower than the time scale of relaxation in the solvation coordinate, (b) the rate is about half of the transition-state theory prediction, and (c) the coupling between the motions along the torsional angle and the solvation coordinate is relatively small.