Abstract
Dual fluorescence of the ground state dimer of highly polar molecules of 3,5-dialkyl-4-methoxybenzylidenemalononitrile in 3-methylpentane solution at low temperature was investigated by steady-state and nonsecond fluorescence spectroscopies. The dimerization of these compounds was confirmed by concentration dependence of absorption and fluorescence spectra at 77 K. The dimer exhibits dual fluorescence consisting of a short-lived dimer fluorescence and a long-lived excimer fluorescence, while the monomer is almost nonfluorescent at room temperature to 77 K. The excimer formation by an orientational relaxation from the excited state of the dimer was discussed in terms of determination of the activation barrier and the fluorescence polarization.