Intrinsic and Extrinsic Heavy‐Atom Effects on the Multifaceted Emissive Behavior of Cyclic Triimidazole

• Published in: Chemistry : a European journal 2019-02, Vol.25 (10), p.2452-2456
• Main Authors: Lucenti, Elena, Forni, Alessandra, Botta, Chiara, Giannini, Clelia, Malpicci, Daniele, Marinotto, Daniele, Previtali, Andrea, Righetto, Stefania, Cariati, Elena
• Format: Article
• Language: English
• Subjects: Chemistry; co-crystals; Crystals; halogen bonding; Materials engineering; Organic crystals; Phosphorescence; photophysics; time-resolved spectroscopy
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201804980

Considering that heavy halogen atoms can be used to tune the emissive properties of organic luminogens, the understanding of their role in photophysics is fundamental for materials engineering. Here, the extrinsic and intrinsic heavy‐atom effects on the photophysics of organic crystals were separately evaluated by comparing cyclic triimidazole (TT) with its monoiodo derivative (TTI) and its co‐crystal with diiodotetrafluorobenzene (TTCo). Crystals of TT showed room‐temperature ultralong phosphorescence (RTUP) originated from H‐aggregation. TTI and TTCo displayed two additional long‐lived components, the origin of which is elucidated through single‐crystal X‐ray and DFT/TDDFT studies. The results highlight the different effects of the I atom on the three phosphorescent emissions. Intrinsic heavy‐atom effects play a major role on molecular phosphorescence, which is displayed at room temperature only for TTI. The H‐aggregate RTUP and the I⋅⋅⋅N XB‐induced (XB=halogen bond) phosphorescence on the other side depend only on packing features. Heavy halogen atoms can tune the emissive properties of organic luminogens both extrinsically and intrinsically. Here, the two effects were investigated by comparing cyclic triimidazole (TT) with its monoiododerivative (TTI), and its co‐crystal with diiodotetrafluorobenzene (TTCo). TTI showed a unique XB‐supported (XB=halogen bond) quadruple‐helix motif in its crystal structure.