SPECTROSCOPIC OBSERVATION OF CONTACT ION-PAIRS FORMED FROM PHOTOLYZED TMPD AND TMB IN THE PRESENCE OF HALOGENATED COMPOUNDS IN NONPOLAR-SOLVENTS

Flash photolysis at 308 nm has been employed to detect contact ion pairs (CIP) formed from excited N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) and N,N,N',N'-tetramethylbenzidine (TMB) in CCl4 solvent and in benzene solutions containing halogenated compounds AX (CCl4 C2H5I, C2H5Br, C6H5I, C6H5Br, and C6H5-Cl). Transient absorption spectra in CCl4 solvent indicate the formation of CIPs for both TMPD and TMB. While the transient spectra for benzene solutions without AX show the formation of only the excited tripler state of TMPD or TMB, those with AX indicate the formation of the corresponding CIP with different mechanism between TMPD and TMB, from the excited tripler state for TMPD, and from direct excitation of weakly-bound heteromer for TMB. The rates and efficiencies for the CIP formation depend on the AX molecule. The present results support the mechanism of CIP formation suggested previously in the microwave dielectric absorption studies.