Katritzky salt fluorophores: Facile synthesis, bright solid-state emission, and mechanochromic luminescence

Katritzky Salts, readily synthesized from condensation between pyrylium salts and amines, were found to be bright solid-state fluorescent emitters. All these ionic fluorophores exhibited remarkable emission enhancement in the DMSO-H2O mixture with raising water fraction, which was identical to classical aggregation induced emission luminogens (AIEgens). After detailed investigation of their photoluminescence behavior in different solvents, the emission enhancement was attributed to polarity changes of solvent mixtures at low volume fraction of water, and aggregate formation at high volume fraction of water. Single crystal structures of TPP3 had directly indicated that the intermolecular pi-pi stacking interactions between fluorophores were severely suppressed as a result of their highly twisted structures, which had consequently contributed to the high emission quantum yield in the solid state. Furthermore, owing to intramolecular free rotations within these propeller-shaped ionic luminogens, obvious mechanochromic luminescence behavior was also observed with red-shifted emission after grinding and blue-shifted emission after solvent annealing.

Automated summary

Katritzky salts, synthesized from condensation between pyrylium salts and amines, are bright solid-state fluorescent emitters that exhibit remarkable emission enhancement in DMSO-H2O mixture, similar to classical AIEgens. The emission enhancement is attributed to changes in solvent mixture polarity at low volume fraction of water, and aggregate formation at high volume fraction of water. The high emission quantum yield in solid state is due to suppressed intermolecular pi-pi stacking interactions between fluorophores and propeller-shaped ionic luminogens also show mechanochromic luminescence behavior.