Imidazole-Based Excited-State Intramolecular Proton-Transfer (ESIPT) Materials:  Observation of Thermally Activated Delayed Fluorescence (TDF)

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2007-10, Vol.111 (39), p.9649-9653
• Main Authors: Park, Sanghyuk, Kwon, Oh-Hoon, Lee, Young-Shin, Jang, Du-Jeon, Park, Soo Young
• Format: Article
• Language: English
• Subjects: Chemistry, Physical - methods; Enzyme Inhibitors - chemistry; Enzyme Inhibitors - pharmacology; Hot Temperature; Imidazoles - chemistry; Imidazoles - pharmacology; Kinetics; Models, Chemical; Protons; Spectrometry, Fluorescence - methods; Spectrophotometry - methods; Temperature; Thermodynamics; Time Factors
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp072212p

We report the first observation of thermally activated delayed fluorescence (TDF) from an excited-state intramolecular proton-transfer (ESIPT) molecule, a hydroxyl-substituted tetraphenyl imidazole derivative (HPI−Ac), in degassed solutions as well as in low-temperature organic matrixes. In the absence of oxygen, the blue emission of an identical spectral feature was observed in the nanosecond (∼4.4 ns) and microsecond (∼25 μs) time domains, and the fluorescence intensity increased with temperature. From the temperature dependence of the time-resolved spectra of HPI−Ac, the energy gap between the first-excited singlet state and the lowest triplet state was determined to be 7.6 ± 0.3 kJ/mol (630 ± 25 cm-1), and the limiting rate constant of intrinsic reverse intersystem crossing was estimated to be 1.3 (±0.5) × 107 s-1.