LASER FLASH-PHOTOLYSIS STUDIES AND MAGNETIC-FIELD EFFECT ON A NEW HETEROEXCIMER BETWEEN N-ETHYLCARBAZOLE AND 1,4-DICYANOBENZENE IN HOMOGENEOUS AND HETEROGENEOUS MEDIA

The electron transfer (ET) process between a fluorophore (N-ethylcarbazole) and a quencher (1,4-dicyanobenzene) has been studied by absorption, steady-state and time-resolved fluorescence and laser flash photolysis techniques in homogeneous and micellar media. The effect of a magnetic field on the ET process of this system has also been carried out by flash photolysis. The results reflect the following unique features of this system. The reduction potentials of the acceptor and the donor are such that the exciplex formation is possible by ET, moreover, as the charge separation is small a weak exciplex is formed even in a highly polar solvent, eg. acetonitrile (MeCN). Thus, the exciplex formation and solvent-separated ion pair (SSIP) formation in MeCN take place simultaneously. The experimentally obtained bimolecular quenching constant, k(q), from the Stern-Volmer plot, agrees satisfactorily with theoretically calculated k(q) for an ET reaction applying Marcus theory. The exciplex formation inside the micellar medium enables us to study the magnetic field effect (MFE) on this exciplex system. The simultaneous occurrence of the exciplex and radical ion pair in MeCN as well as the formation of the exciplex within the micellar environment, most probably for the first time, ensure a special characteristic of this exciplex system. Another novel feature is the abnormal behaviour of this system in benzene, which has also been discussed here.