Magnetic field effect on pyrene/N,N-dimethylaniline exciplex luminescence has been studied. Concept of un-relaxed (emitting at the blue end of the emission band) and relaxed exciplexes in polar solvents has been introduced. Bi-exponential decay of pyrene in condensed phase has been established which is explained on the basis of complex formation of excited pyrene with solvent molecules. The measurement of B1/2 values of the exciplex system in various neat and binary solvents throws light on the size of the transient, dielectric enriched micro-domains in binary solvents around the radical ion pair (RIP) after electron transfer. Life-time studies of the exciplex emission at various neat and binary solvents of varying permittivity reflect the possibility of lowering of radical ion pair energy below that of excited triplet pyrene at very high permittivity. Finally various instrumentation detail and electronic tricks to achieve high signal to noise ratio in magnetic field effect measurements employing lock-in technique has been discussed.

PROF.DR.DEB NARAYAN NATHSenior Professor Department of Physical Chemistry IACSJadavpur, Kolkata 700 032,India Born April 30, 1955, Kolkata. Ph.D. (1989), Jadavpur University, Supervisor:Prof. M. Chowdhury, IACS. Research interests:Magnetic Field Effects on Radical Pair Systems,Instrumentation