Photophysics of 9-amino acridine hydrochloride hydrate single microcrystals

Single microcrystals of 9-amino acridine hydrochloride hydrate (9AAHH) have been studied by steady state and time resolved fluorescence microscopy. Crystalline 9AAHH exists in the form of two types of microcrystals viz., stick type and slab type. The stick-shaped microcrystals are found to undergo excimer formation. With increase in size, the excimer fluorescence is masked by the concomitant appearance of self-absorption effect in dimer. The fluorescence lifetimes increase on increasing the microcrystal size. While the bandwidth of fluorescence spectra of slab shaped microcrystals are found to increase, the fluorescence lifetimes decrease with increasing their size. Results are explained on the basis of interplay between the self-absorption effect of the dimer, its conversion efficiency to the excimer, and higher aggregate formation in large microcrystals.