The dynamics of excited state structural relaxation of 4-dimethylaminobenzonitrile (DMABN) and related compounds

• Main Authors: Valery Volchkov, Lyubov' Uzhinova, Boris Uzhinov
• Format: Article
• Language: English
• Published: Hindawi Limited 2006-01-01
• Series: International Journal of Photoenergy
• Online Access: http://dx.doi.org/10.1155/IJP/2006/81896

The excited state structural relaxation of 4-dimethylaminobenzenes with various para-acceptor substituents having double-band emission, local excited (LE) and charge transfer (CT), has been investigated. Fluorescence measurements at different temperatures and in different solvents have confirmed the existence of viscosity-dependent, temperature, and polarity-activated relaxation. The kinetics analysis has shown that the radiative deactivation rate constants of the individual LE and CT states differ by 7–112-fold. The dipole moment changes at the excitation for CT states are significantly larger than those for LE states. The spectral-kinetics behavior of compounds studied agrees with the models A→A∗→B∗ or A→A∗↔B∗, where A∗ is the local excited planar and B∗ is the relaxed twisted state of the molecule. The rate constants of the twisted state formation have been calculated in the temperature range 293–77 K. The activation energies of forward process for compounds studied have been estimated.