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Photophysical Properties and Efficient, Stable, Electrogenerated Chemiluminescence of Donor–Acceptor Molecules Exhibiting Thermal Spin Upconversion
Author(s) -
Ishimatsu Ryoichi,
Edura Tomohiko,
Adachi Chihaya,
Nakano Koji,
Imato Toshihiko
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201600077
Subject(s) - photochemistry , molecule , singlet state , acceptor , chemistry , photon upconversion , steric effects , dichloromethane , polymerization , fluorescence , chemiluminescence , electron acceptor , excited state , stereochemistry , ion , organic chemistry , polymer , physics , quantum mechanics , solvent , nuclear physics , condensed matter physics
The photophysical properties and electrogenerated chemiluminescence (ECL) of three donor–acceptor molecules composed of dicyanobenzene and methyl‐, tert ‐butyl‐, and phenyl‐substituted carbazolyl groups, 1,2,3,5‐tetrakis(3,6‐disubstituted ‐ carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN‐Me, 4CzIPN‐ t Bu, and 4CzIPN‐Ph, respectively) are described. These molecules show delayed fluorescence as a result of thermal spin upconversion from the lowest triplet state to the lowest singlet state at room temperature. The three molecules showed yellow to yellowish–red ECL. Remarkably, the ECL efficiencies of 4CzIPN‐ t Bu in dichloromethane reached almost 40 %. Moreover, stable ECL was emitted from 4CzIPN‐ t Bu and 4CzIPN‐Ph. In case of 4CzIPN‐Me, the ECL intensity decreased during voltage cycles because of polymerization. Quantum chemical calculations revealed that polymerization was inhibited by the steric hindrance of the bulky tert ‐butyl and phenyl groups on the carbazolyl moieties and lowered the spin density on the carbazolyl groups through electron conjugation for 4CzIPN‐Ph.