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

Ryoichi Ishimatsu, Tomohiko Edura, Chihaya Adachi, Koji Nakano, Toshihiko Imato

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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-tBu, 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-tBu in dichloromethane reached almost 40 %. Moreover, stable ECL was emitted from 4CzIPN-tBu 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. Delayed fluorescence: Because of thermal spin upconversion of donor-acceptor molecules, efficient electrogenerated chemiluminescence (ECL) was realized (see figure; ISC: Intersystem crossing, RISC: Reverse intersystem crossing). Moreover, methyl, tert-butyl, and phenyl substituents on the donor-acceptor molecule enhance the ECL stability.

Original languageEnglish
Pages (from-to)4889-4898
Number of pages10
JournalChemistry - A European Journal
Volume22
Issue number14
DOIs
Publication statusPublished - Mar 24 2016

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All Science Journal Classification (ASJC) codes

  • Catalysis
  • Organic Chemistry

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