Molecular and supramolecular room temperature phosphorescences from metal free carbonyl functionalized triazinic scaffold

The photophysical behavior in solution, PMMA films and crystals of PhCHO mono-, TTPhCHO, and tri-substituted, TT(PhCHO)3, cyclic triimidazole (TT) derivatives is here reported and analyzed through computational and X-ray diffraction studies. The two compounds are poorly fluorescent in diluted solution but display aggregation-induced emissive, AIE, behavior in the solid state where molecular and multiple supramolecular long lived radiative deactivation channels are turned on. In particular, in PMMA films, TTPhCHO is mailny fluorescent while TT(PhCHO)3 is only phosphorescent. In crystals, both compounds show exclusively long lived components of molecular (HEP), CHO⋯TT (MEP) and π–π (TT-TT or TT-Ph, LEP) supramolecular origin as disclosed through theoretical and single crystal X-ray diffraction analysis. The different behaviour observed in PMMA films has been assigned to the easier S–T intersystem crossing associated with the three vs. one carbonyl substituents in TT(PhCHO)3 and TTPhCHO, respectively.