Intramolecular Triple Cyclization Strategy for Sila‐ and Oxa‐Analogues of Truxene with Long‐Lived Phosphorescence

• Published in: Asian journal of organic chemistry Vol. 6; no. 3; pp. 290 - 296
• Main Authors: Ogaki, Takuya, Ohta, Eisuke, Oda, Yukiko, Sato, Hiroyasu, Matsui, Yasunori, Kumeda, Motoki, Ikeda, Hiroshi
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-03-2017
• Subjects: aromatic substitution; fused-ring systems; heterocycles; Organic chemistry; phosphorescence; truxene
• ISSN: 2193-5807; 2193-5815
• DOI: 10.1002/ajoc.201600560

Trisilatruxene and trioxatruxene were synthesized by intramolecular triple cyclization of triphenylbenzene derivatives. The results of photophysical studies with these substances show that absorption, fluorescence, and phosphorescence of trisilatruxene appear at longer wavelengths compared to those of hexamethyltruxene. The results of DFT calculations suggest that these effects are a consequence of a decrease in the energy of the LUMO caused by σ*–π* orbital interactions in the silole rings. In contrast, trioxatruxene absorbs and emits light at shorter wavelengths than those of hexamethyltruxene as a result of aromatic stabilization of the furan rings. Moreover, all of the truxenes display long‐lived phosphorescence with lifetimes in the range of 4.4–16.4 s, attributable to the symmetry‐forbidden nature of T1→S0 transitions essentially linked with the C3‐symmetric structures.
Trisilatruxene and trioxatruxene, respective sila‐ and oxa‐analogues of truxene, were synthesized by employing a new intramolecular triple cyclization strategy. These compounds together with hexamethyltruxene display long‐lived phosphorescence with the lifetime of 4.4–16.4 s at a low temperature. The long lifetimes are attributable to the symmetry‐forbidden T1→S0 transitions, being essentially linked with the C3‐symmetric structures.