ANOMALOUS SOLVENT EFFECTS ON THE TWISTED INTRAMOLECULAR CHARGE-TRANSFER FLUORESCENCE OF ETHYL 4-(N,N-DIMETHYLAMINO)BENZOATE IN CHLORINATED SOLVENTS

It was found that the TICT (twisted intramolecular charge transfer) fluorescence of the title compound was very different in chlorinated solvents in comparison with other solvent systems. The emission energy from the a* state (charge transfer state) is higher and the intensity ratio, R = Ia/Ib where Ia and Ib are the emission intensity from the a* state and from the local excited state, is lower at room temperature in CHCl3 and butyl chloride than in nonchlorinated solvents. The activation energies E1 and E2 for the forward (b* → a*) and backward (b* ← a*) reactions are also higher in chlorinated solvents. The origin of the anomalous solvent effects was attributed to donor-acceptor type solute-solvent interaction. This interaction was thought to affect the potential energy hypersurface along the reaction path: b* → a*. An anomalous red-shift of the a* band of polymer-bound TICT chromophore in chlorinated solvents was discussed in terms of reduced solvation. © 1990 American Chemical Society.