TEMPERATURE DEPENDENCE OF PHOSPHORESCENCE LIFETIME OF BENZENE AND N-ALKYLBENZENES BETWEEN 4.2 AND 100 DEGREES K

The temperature dependence of the phosphorescence lifetime of benzene and its n-alkyl derivatives C6H5CnH2n+1, n = 1 to 13, has been measured in a rigid glass of a mixture of methylcyclohexane-isopentane (4:1 by volume) between 4.8 and 100°K. The phosphorescence lifetime is temperature independent below about 60°K, depending on the solute, and temperature dependent in a relatively small temperature range at higher temperatures. Arrhenius plots indicate that in this region there are two or more paths of externally influenced non-radiative decay contributing to the decay of the triplet state. The incoherence in previously reported data of phosphorescence lifetimes at 77°K of a specific molecule can be attributed to temperature and solvent effects while those at 4.2°K can be attributed solely to solvent effects. The phosphorescence lifetimes of the n-alkylbenzenes depend on the chain length of the alkyl substituent, but no simple relation to other molecular parameters has been found.