How Fluorophore Connectivity Can Affect Aggregate State Emissions: a Case Study

Recently, cyclic triimidazole (TT) has revealed Crystallization Induced Emissive behaviour with a solid state photoluminescent quantum yield equal to 30% due to concomitant fluorescence and ultralong phosphorescence (up to 1 s).1a Moreover, it has been used as an intriguing scaffold for the preparation of new fully organic room temperature phosphorescent (RTP) materials, luminescent coordination complexes, polymers and bio-probes.1 Among the TTs family, TT-Carbazole compounds with different connections between the two units, namely a CTT-CCz bond in TT-(C)-Cz or a CTT-NCz one in TT-(N)-Cz and a phenyl spacer in TT-Ph-Cz (Figure 1), have been prepared and fully characterized.2 The three compounds display in diluted solution, blended films and powders, excitation-dependent emissive behavior with both short and long-lived emissions. Remarkably, TT-(N)-Cz and TT-Ph-Cz have been isolated in different polymorphs displaying structural and crystalline grade-dependent photophysics. Furthermore, TT-Ph-Cz crystallizes as MeOH-solvated and de-solvated forms which are able to interconvert through Single-Crystal to Single-Crystal transition (desolvation) and MeOH uptake (vapochromism) restoring emissive properties. The multifaceted emissive behavior of TT-Ph-Cz is enriched by dual fluorescence and phosphorescence, RTP from aqueous aggregate and mechanochromism leading to an interesting stimuli-responsive high-performance single-component luminescent material. References [1] a) E. Lucenti, E. Cariati, et al. J. Phys. Chem. Lett. 2017, 8, 1894-1898; b) E. Lucenti, E. Cariati, et al. Angew. Chem. Int. Ed. 2017, 56, 16302-16307; c) A. Previtali, B. Z. Tang, E. Cariati, et al. Chem. Eur. J. 2021, 27, 16690-16700. [2] a) D. Malpicci, E. Cariati, et al. Dyes Pigm. 2023, 215, 111274; b) D. Malpicci, E. Cariati, et al. Chem. Eur. J. 2023, 29, e202300930.