Revisiting Dual Intramolecular Charge-Transfer Fluorescence of Phenothiazine-triphenyltriazine Derivatives

The photophysical properties of the phenothiazine-triphenyltriazine derivative, PTZ-TRZ, are reinvestigated. The results, in combination with the computational approaches, lead us to draw the conclusion that the complicated excitation behavior in toluene (ref (18)), in part, is due to the UV absorption cutoff region for toluene where the <315 nm excitation is greatly distorted by solvent absorption, i.e., the inner filter effect, in a regular sample cuvette (1.0 cm path length). Switching the solvent to cyclohexane with the UV cutoff wavelength at 235 nm simplifies the results. In cyclohexane, two isomers exist for PTZ-TRZ in the ground state and quasi-axial and quasi-equatorial conformers. Upon electronic excitation, both quasi-axial and quasi-equatorial conformers undergo structural relaxation to an energy minimum state where the phenothiazine is in a planar configuration.