Excited state dipole moments of 4-(dimethylamino)benzaldehyde

The effect of various polar solvents on the location of absorption and dual fluorescence (short wavelength emission, SE, and long wavelength emission, LE) of 4-(dimethylamino)benzaldehyde (DMABA) at room temperature was investigated. It was found that the fluorescence intensities ratio LE/SE is constant for concentrations ranging from 10−5 M to 10−1 M, which evidences that the LE-band is not of excimer origin. on the batochromic shift of electronic spectra of DMABA and Bilot–Kawski theory the values of excited state dipole moments in SE: μ e SE = 7.6 D and the Onsager radius a = 4.3 Å were found using the known from literature value of ground state dipole moment μg = 5.6 D. For the emitting twisted intramolecular charge transfer (TICT) excited state the value of μ e LE = 12 D was found.