Photophysical Properties and Efficient, Stable, Electrogenerated Chemiluminescence of Donor–Acceptor Molecules Exhibiting Thermal Spin Upconversion

Abstract 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.