Abstract: The appearence of the new fluorescence peak at about 570 nm demonstratesexciplex formation between the singlet states of 9-vinyl anthracene and p-H, M-dimethy-lamino stytene.With increasing the polarity of solvents, the red-shift of the emission wavelength occurs and the fluorescence quantum yield of the exciplex decreases.For example,thefluorescence peak is at 550 nm in totuene and at 595 nm in butanone.The fluorescence qua-tum yields in totuene and in butanone are 0.053 and 0 respectively.Both the relative yield ofthe photocycloaddition dimer and the ratio of the relative yields of the trans and cis dimers decrease with increasing the polarity of solvents.For example,the relative yields of the dimerare 1.0 in totuene and 0.04 in butanone respectively.The ratio of the relative yields of transand cis dimers are 0.54 and 0 in totuene and butanones, respectively.In addition, the exciplex intermediate mechanism was suggested for the photocycloaddition between 9-vinyl anthracene and 9-N,N-dimethylamino styrene.

Key words: Exciplex, Photocycloaddition, 9-Vinyl anthracene