Fluorescence emission enhancement in substituted 3-styrylindoles in the solid state

Fluorescence emission properties of substituted 3-styrylindoles viz 3-(2-phenylethenyl-E)-NH-indole (1), 3-[2-(4-cyanophenyl)ethenyl-E]-NH-indole (2), and 3-(2-cyano-2-phenylethenyl-Z]-NH-indole (3) in n-hexane, THF–H2O binary mixtures and solid state are reported. In general, fluorescence efficiency in solid state is found to be much higher than in n-hexane solution. The fluorescence enhancement in solid state is attributed to restricted intramolecular motions. Interestingly, the molecules of 3 in solid state are also bound together through intermolecular hydrogen bonds yielding polymer like structure, leading to further enhancement of fluorescence emission. In THF–H2O binary mixtures, drastic enhancement of fluorescence efficiency is observed due to aggregate formation.