Dual fluorescence and RTP features of carbazole-cyclic triimidazole derivatives: The fluorophores' connectivity does matter

Organic room temperature phosphorescent (ORTP) materials with stimuli responsive behaviour are extremely desirable for various applications. Two derivatives of cyclic triimidazole (TT) functionalized through a different connectivity with carbazole (Cz) are investigated. The two compounds possess quite different emissive behaviour associated with both molecular reasons and aggregation modes. In TT-(N)-Cz, having a C-N bond connecting Cz to the triimidazole unit, the twisted molecular conformation results in the absence of electronic communication between the two moieties. It crystallizes in two polymorphs (TT-(N)-CzM and TT-(N)-CzT) showing structure dependent dual fluorescence and dual phosphorescence, both of molecular and aggregate origin with aggregation induced fluorescence component highly sensitive to grinding. In TT-(C)-Cz, having the two moieties connected through a C-C bond, the much-reduced twisting allows higher electronic communication resulting in a single red shifted fluorescence. Moreover, crystals of TT-(C)-Cz display long lived components of molecular and supramolecular origin.