Unimolecular Decay of the Triplet State of Anthracene in Fluid and Viscous Media

Abstract

The rate of decay of the triplet state of anthracene, dissolved in hexane, tetrahydrofuran, and glycerol, has been measured at temperatures ranging from 30 to -70°C. In fluid solvents at ordinary temperatures, the decay appears to be chiefly the result of bimolecular triplet-triplet interaction and of a bimolecular quenching reaction involving an unknown quencher, present in trace amounts even in highly purified solvents. In addition, there appears to be a unimolecular, temperature-independent decay, corresponding to an intrinsic mean life of about 0.01 sec. In glycerol, the first-order rate constant decreases rapidly with decreasing temperature, approaching a limiting half life of about 0.04 sec at -25°C. This limiting rate appears to be the same as has been previously reported for solutions in EPA at liquid nitrogen temperatures. Similar results were obtained with solutions of dibenzanthracene.

Temperature dependence of the lifetime of phosphorescence of some polynuclear hydrocarbons in viscous solution

“…The data presented in ref. (8) and (9) which were obtained at temperatures above -78°C are consistent with the relation, k = a+c' exp (-E/RT) (sec-1).…”

“…There have been many studies of the kinetics of triplet decay at room temperature in fluid solvents [1][2][3][4] and at low temperatures in rigid media.5-7 With a few exceptions, little attention has been given to the temperature region between these extremes. [8][9][10][11] In this work, first-order triplet decay constants of some aryl hydrocarbons were measured in three viscous solvents : glycerol, propylene glycol, and 3-methylpentane, which was used only below -140'. The phosphorescence lifetimes of 1,2,5,6-&benzanthracene, triphenylene, naphthalene, 2-chloronaphthalene and 2-iodonaphthalene in one or more of the above solvents, were measured from 77°K to as high a temperature as proved practicable.…”

Separation of viscosity and temperature effects on the singlet pathway to stilbene photoisomerization

“…Application of the Model to Triplet State Systems. Triplet-triplet absorption [47][48][49][50][51][52][53] and phosphores-cence495354 measurements have revealed large viscosity effects on radiationless decay processes of the lowest triplet states of many compounds, which are generally manifested in a strong temperature depen-dence of the apparent first-order rate constant for triplet decay, with the particular temperature range depending upon the solvent. However, most of these effects are almost certainly due to changes in intermolecular quenching rates involving small concentrations of unknown impurities and/or photoproducts,48'5155 and do not represent viscosity effects on unimolecular decay processes of the triplet state.…”

Temperature dependence of the phosphorescence lifetime of benzene and n-alkylbenzenes between 4.2 and 100.deg.K

“…The temperature dependence of the phosphorescence lifetimes has been described previously. [3][4][5][6][7][8][9][10][11][12][13] Although it is commonly accepted that the temperature is not the only factor that affects the lifetimes, this effect will be referred to as "temperature effect" in this paper. Experiments suggest that changes in the viscosity of the solvent seem to be the main factor contributing to this effect, but no coherent relationship between viscosity and the phosphorescence lifetimes has been offered.6-7,10,27'28 Some authors3-6 claim unknown quenchers are responsible for the temperature dependence and the deviations of the phosphorescence decay from first order when the matrix is melting.…”