The heavy atom effect on the phosphorescence of aromatic hydrocarbons. Part 3.—Quenching of perdeuterated benzene by alkali halides

Abstract

The effects of varying concentrations of alkali halides, as external heavy atom perturber, on the phosphorescence of perdeuterated benzene were investigated in rigid matrices of ethyl alcohol at liquid nitrogen temperature, in order to determine whether the charge-transfer or the exchange mechanism of quenching was operative. It was found that the dark decay processes can be rationalized by assuming the formation of exciplex (1 : 1 molecular complex of excited molecule and heavy atom perturber). Decay rates computed for the various exciplexes fell in the range 0.45-0.60 s^–1. The equilibrium constants of exciplexes were estimated and compared with those of naphthalene-d₈. These values (0.33-1.60 l. mol^–1) were of the same order of magnitude as those of the ordinary charge-transfer complexes and were within the expectation limits, thereby providing further support for the proposed charge-transfer mechanism.