An improved phase-locked detection system for the observation of the magnetic field effect on exciplex luminescence: deviation from previously observed dielectric constant dependence

The magnetic field effect (MFE) on exciplex luminescence was studied using an improved phase-locked detection system. The sensitivity of the instrument gives a precise measurement of a very low percentage change in MFE (of the order of 0.01%) which has not been obtained previously. A comparative study of the dependence of MFE on the dielectric constant (epsilon) of the medium was carried out using two exciplex systems: pyrene-N,N-dimethylaniline (Py-DMA), a well-studied exciplex system, and N-ethyl carbazole-l,4-dicyanobenzene(ECZ-DCB), a recently explored exciplex system. For ECZ-DCB, the MFE was obtained around epsilon approximate to 9 (epsilon(max)), which is far lower than the usual limit of 14<epsilon(max) < 18 observed in Py-DMA and other exciplex systems, with the onset at epsilon=6. This result was explained on the basis of the different charge transfer characteristics of the two systems. (C) 1997 Elsevier Science S.A.