EXCITED-STATE DYNAMICS OF NITROBENZENE STUDIED BY THE TIME-RESOLVED TRANSIENT GRATING METHOD

The nonradiative relaxation processes from the photoexcited nitrobenze ne (NB) have been directly detected using the time-resolved transient grating (TG) method. From the heat-releasing rates of NB in heptane, a relatively short lifetime of the lowest excited singlet state (less t han or equal to 20 ps) as well as a surprisingly short lifetime of the lowest excited triplet state (similar to 400 ps) are detected. By mea suring the heat energies from the excited NB, the quantum yield of the triplet formation (Phi(isc)) and the energy of the lowest excited tri plet state (E(T)) are found to be greater than or equal to 0.80 and 22 similar to 27 x 10(3) cm(1). The photophysical properties of NB are a lso discussed.