Dual flrorescence of anilino substituted benzanilides in non-polar solvent cyclohexane - Direct spectroscopic evidence for the excited-state charge transfer

Abstract

The fluorescence spectra in cyclohexane of a series of benzanilides(BAs) with different para-substituents at the anilino moiety revealed that BAs emitted dual fluorescence 9 with one normal weak emission at ca. 330 nm and An abnormally long-wavelength emission ranging from 460, to 550 nm. The long-wavelength emission was found strongly dependent of the electron donating capacity of the substituent at the anilino moiety aria a stronger electron donating substituent led to a red-shift in the emission., The energies of the long-wavelength emission of the BAs were correlated to the oxidation potentials of the donors, E-D/D+, and a nice linear correlation was found with a slope of +0. 66, which clearly pointed to the charge transfer character of the emissive state for the long-wavelength emission and the high decoupling extent of the charges in the CT state. This is the first report that shows the direct evidence for the CT nature. The results might be of significance in understanding the photophysics of peptide and protein and in designing novel fluorescent chemosensors.