Dual Fluorescence of Fluorazene in Solution: A Computational Study

The fluorazene molecule presents dual fluorescence in polar solvents. Its absorption and emission properties in gas phase and in acetonitrile solution have been studied theoretically using the complete active space second-order perturbation//complete active space self-consistent field quantum methodology and average solvent electrostatic potential from molecular dynamics for the solvent effects. In gas phase, two optimized excited-state geometries were obtained, one of them corresponds to a local excitation (LE), and the other is an intramolecular charge transfer (ICT) and lies higher in energy. In acetonitrile solution, a second ICT structure where the molecule remains planar is found, and the energy differences are reduced. Fluorescence energies from LE and the planar ICT have a good agreement with the experimental bands, but emission from the bent ICT has too low an energy.