Localized excitation effects in (E,E)-2,5-bis[2-(4-N,N-dipropylaminophenyl) ethylenyl]-3,6-dimethylpyrazine and generation of its different forms in solution

Dipole moments of (E,E)-2,5-bis[2-(4-N,N-dipropylaminophenyl)ethylenyl]-3,6-dimethylpyrazine (VS365) quadrupolar dye in 1,4-dioxane and cyclohexane in addition to its instantaneous fluorescence spectra and fluorescence lifetimes in dichloromethane (pure and with added trifluoroacetic acid) were measured. Quantumchemical calculations show that the π − π conjugated system is localized in the flattest part of the molecule due to disorder in the ground-state geometry of the dye molecule and that this part is the one responsible for light absorption. The effect of localized excitation of the dye causes a considerable change in its dipole moment Δaμ. Various fluorescent forms of the dye that feature considerably spaced emission spectra and different fluorescence lifetimes originate by adding trifluoroacetic acid to the solution of oligophenylenevinylene in dichloromethane.