The optical signature of 2,6-bis((E)-2-(benzoxazol-2-yl)vinyl)naphthalene (BBVN) laser dye: a TDDFT study

Abstract

The photophysical properties of the 2,6-bis((E)-2-(benzoxazol-2-yl)vinyl)naphthalene (BBVN) laser dye have been investigated by time-dependent density functional theory (TDDFT) using the BMK functional in the gas phase and solvents. Upon photon absorption, the dye undergoes an intense ππ* transition polarized along the long molecular axis. The natural transition orbital (NTO) representation of excitation indicates that the benzoxazole nucleus provides a room for a larger charge displacement in absorption/emission. The calculated small value of Stokes shift together with the root-mean-square distance demonstrates that the excited state (S₁) geometry is not significantly displaced from that of the ground state (S₀). Using a panel of solvation models (LR-PCM, cLR-PCM, and SS-PCM) we have shown that the solvent hardly has an impact on absorption but has a slight positive solvatochromic effect on fluorescence. The calculated E^0–0 energy agrees with the experimental absorption-fluorescence crossing point (AFCP). The vibronic band simulation supports the vibronic origin of the measured spectra. Owing to its large oscillator strength, short fluorescence lifetime, high photo-stability and increased rigidity in the excited state, the BBVN dye meets the necessary requirements for being a good laser dye.