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 ), 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.