A time resolved EPR study of the lowest excited triplet states of agr;hyphen;chloroanthraquinones

摘要

Time resolved EPR and optically detected magnetic resonance (ODMR) experiments were performed on the lowest excited triplet (T1) states of agr;hyphen;chloroanthraquinones at low temperatures (77ndash;1.4 K). In contrast to the case of anthraquinone smaller zero field splittings (zfs; 4ndash;6 GHz) were obtained for 1hyphen;chloroanthraquinone (1ClAQ) and 1,5hyphen;dichloroanthraquinone (1,5DClAQ). And unusually small zfs (lsim;1.2 GHz) were obtained for 1,8hyphen;dichloroanthraquinone (1,8DClAQ). The vibrational analyses of the phosphorescence spectra of 1 ClAQ and 1,5DClAQ were made. Long progressions ofntimes;184(201) cmminus;1bands were ascribed to the Cndash;Cl bending mode, which indicates distorted structures of theT1states. It is concluded that theT1states of 1ClAQ and 1,5DClAQ show intermediate characters between those of3npgr;ast; AQ andT1of 1,8DClAQ. The possibility ofT11,8DClAQ being a3pgr;pgr;ast; or a mixed3pgr;pgr;ast;ndash;3npgr;ast; state is denied on the basis of the obtained results, particularly very small zfs. Anpgr;ast; (n=an0minus;bnCl;ab0) state with a delocalizednelectron is suggested as a possible candidate forT1of 1,8DClAQ.