Room temperature phosphorescence and stimuli responsive behavior of cyclic triimidazole derivatives

Cyclic triimidazole (TT) has recently revealed as an interesting scaffold for the preparation of new fully organic room temperature phosphorescent (RTP) materials, luminescent coordination complexes, polymers and bio-probes. TT itself displays at room temperature 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).1 The introduction of either halogen atoms or chromophoric fragments opens to molecular systems featured by a complex photoluminescence comprising dual fluorescence and multiple molecular and supramolecular phosphorescences.2, 3 Among the recently reported derivatives, a new family of TT-Carbazole compounds has been isolated. Specifically, three different molecules have been prepared 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 (see Scheme 1).4, 5 The three compounds display in diluted solution, 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 a structural and crystalline grade-dependent photophysics. Moreover, TT-Ph-Cz crystallizes as MeOH-solvated (monoclinic) and de-solvated (triclinic and orthorhombic) forms characterized by distinctive emissive features. The monoclinic phase displays higher quantum yield associated with a strong phosphorescence contribution due to H-Bonds which reduce molecular movements. Notably, triclinic and monoclinic phases 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 (clearly visible in viscous solvents) and phosphorescence, RTP from aqueous aggregate and mechanochromism leading to an interesting stimuli-responsive high-performance single-component luminescent materials. 1. Lucenti, E.; Forni, A.; Botta, C.; Carlucci, L.; Giannini, C.; Marinotto, D.; Previtali, A.; Righetto, S.; Cariati, E., H-Aggregates Granting Crystallization-Induced Emissive Behavior and Ultralong Phosphorescence from a Pure Organic Molecule. J. Phys. Chem. Lett. 2017, 8 (8), 1894-1898. 2. Previtali, A.; He, W.; Forni, A.; Malpicci, D.; Lucenti, E.; Marinotto, D.; Carlucci, L.; Mercandelli, P.; Ortenzi, M. A.; Terraneo, G.; Botta, C.; Kwok, R. T. K.; Lam, J. W. Y.; Tang, B. Z.; Cariati, E., Tunable Linear and Nonlinear Optical Properties from Room Temperature Phosphorescent Cyclic Triimidazole-Pyrene Bio-Probe. Chem. Eur. J. 2021, 27 (67), 16690-16700. 3. Formenti, M.; Blasi, D.; Cariati, E.; Carlucci, L.; Forni, A.; Giannini, C.; Guidotti, M.; Econdi, S.; Malpicci, D.; Marinotto, D.; Lucenti, E., Pyrene-substituted cyclic triimidazole: An appealing and versatile luminescent scaffold for explosive detection. Dyes Pigm. 2022, 206 (August), 110637-110637. 4. Malpicci, D.; Forni, A.; Botta, C.; Giannini, C.; Lucenti, E.; Marinotto, D.; Maver, D.; Carlucci, L.; Cariati, E., Dual fluorescence and RTP features of carbazole-cyclic triimidazole derivatives: The fluorophores’ connectivity does matter. Dyes Pigm. 2023, 215, 111274. 5. Malpicci, D.; Forni, A.; Botta, C.; Giannini, C.; Lucenti, E.; Marinotto, D.; Maver, D.; Carlucci, L.; Cariati, E., Stimuli Responsive Features of Organic RTP Materials: An Intriguing Carbazole-Cyclic Triimidazole Derivative. Chem. Eur. J. 2023, 29 (38), e202300930.