title: Imidazole-based excited-state intramolecular proton-transfer (ESIPT) materials: observation of thermally activated delayed fluorescence (TDF).
abstract: 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 ( approximately 4.4 ns) and microsecond ( approximately 25 micros) 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) x 107 s-1.
authors.affiliation: Department of Materials Science and Engineering, Seoul National University, ENG 445, Seoul 151-744, Korea.
authors.forename: Sanghyuk
authors.initials: S
authors.lastname: Park
authors.forename: Oh-Hoon
authors.initials: OH
authors.lastname: Kwon
authors.forename: Young-Shin
authors.initials: YS
authors.lastname: Lee
authors.forename: Du-Jeon
authors.initials: DJ
authors.lastname: Jang
authors.forename: Soo Young
authors.initials: SY
authors.lastname: Park
mesh_terms: D002627:Chemistry, Physical / Q000379:methods; D004791:Enzyme Inhibitors / Q000737:chemistry* / Q000494:pharmacology; D006358:Hot Temperature; D007093:Imidazoles / Q000737:chemistry* / Q000494:pharmacology; D007700:Kinetics; D008956:Models, Chemical; D011522:Protons; D013050:Spectrometry, Fluorescence / Q000379:methods*; D013053:Spectrophotometry / Q000379:methods; D013696:Temperature; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D007093:Imidazoles; D011522:Protons; C029899:imidazole