Nature of excited singlet and non-phosphorescent triplet states of perinaphthenone

Natures of excited singlet and triplet states of perinaphthenone (PPS) were investigated. Assignment of low-lying excited states was carried out by electronic spectra and CNDO/S-CI molecular orbital calculation. No phosphorescence was observed and an emission reported as phosphorescence was assigned to the emission of PN ketyl radical. Tripler energy and electronic nature of the lowest triplet state were determined by the time-resolved thermal lensing (TRTL) and the time-resolved ESR experiments. The triplet energy was determined to be 164 kJ mol(-1) and the ZFS parameters were determined to be 0.075 and 0.014 cm(-1) for \D\ and \E\ values, respectively. \D\ value of PN indicates that the electronic nature of the triplet state is pi pi*. A liner relationship was confirmed between the triplet energy and the \D\ value. The triplet energy and D value of PN satisfy this relationship. (C) 2000 Elsevier Science S.A. All rights reserved.