An enhanced fluorescence in a tunable face-to-face pi center dot center dot center dot pi stacking assembly directed by the H-bonding

A simple anthryl derivative 1-((anthracen-10-yl)methylene)-4-ethyl-thiosemicarbazide (ANS) shows a methanol-tunable solid state fluorescence enhancement based on different molecular packing structure; the emission is stronger in crystal 2 than that in crystal 1 under the same condition. This is mainly due to the formation of face-to-face pi center dot center dot center dot pi stacking assembly in crystal 2 which is directed and enhanced by intermolecular H-bonding interactions. The observation of fluorescence decay corroborates the formation of an emissive excimer in the pi center dot center dot center dot pi stacking assembly.