title: 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-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.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan. ishimatsu@cstf.kyushu-u.ac.jp.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Ishimatsu
authors.affiliation: Center for Organic Photonics and Electronics Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan.
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Edura
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan. adachi@opera.kyushu-u.ac.jp.|Center for Organic Photonics and Electronics Research, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan. adachi@opera.kyushu-u.ac.jp.|JST, ERATO, Adachi Molecular Exciton Engineering Project, c/o Center for Organic Photonics and Electronics Research, and, International Institute for Carbon Neutral Energy, Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan. adachi@opera.kyushu-u.ac.jp.
authors.forename: Chihaya
authors.initials: C
authors.lastname: Adachi
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Nakano
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395, Japan. imato@cstf.kyushu-u.ac.jp.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Imato
keywords: donor-acceptor systems; electrochemiluminescence; fluorescence; lifetimes; solvent effects