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Triskelion‐Shaped π‐Luminophores Bearing Coumarin: Syntheses, Structures, and Luminescence Properties
Author(s) -
Ueda Masafumi,
Kokubun Mirai,
Mazaki Yasuhiro
Publication year - 2020
Publication title -
chemphotochem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.13
H-Index - 18
ISSN - 2367-0932
DOI - 10.1002/cptc.202000049
Subject(s) - intramolecular force , luminescence , chemistry , molecule , excited state , crystallography , photochemistry , stereochemistry , materials science , organic chemistry , physics , optoelectronics , nuclear physics
Triskelion‐shaped π‐luminophores bearing three coumarin units 1 a and 1 b were successfully synthesized by the intramolecular Ullmann coupling reaction of triphenyl benzene‐1,3,5‐tricarboxylate derivatives. X‐ray crystal structure analysis revealed that compound 1 adopts a unique curved and three‐blade propeller‐shaped structure. These crystals are a racemic mixture consisting of PPP ‐ and MMM ‐ 1 due to the helicity resulting from the steric hindrance. A computational study suggests that this helical inversion process between PPP‐ and MMM ‐ 1 a occurs with comparative ease. The emission spectra of 1 a and 1 b in THF solution showed sharp emission bands at 454 nm and 492 nm, respectively. The Stokes shifts were relatively large at 7385 cm −1 and 6556 cm −1 due to their degenerate frontier molecular orbitals. A solution of 1 b in different organic solvents demonstrated solvatofluorochromism due to intramolecular charge transfer of the coumarin unit in the excited states. Interestingly, both triskelion‐shaped molecules formed aggregates in a mixture of THF‐H 2 O and exhibited aggregation‐induced emission enhancement characteristics.