Abstract

The temperature dependence (10–160 K) of the phosphorescence lifetimes and intensities of 2,4,5-trimethylbenzaldehyde (TMB) in crystalline durene have been investigated. Two phosphorescence bands (407.5 and 411.2 nm) are observed to grow in with increasing temperature, reach a maximum intensity, and decrease in intensity at higher temperatures. Exponential phosphorescence decays are observed in the 10 to 95 K and 110 to 160 K ranges, while non-exponential decays are observed in the 95 to 110 K region. Ultra-violet photolysis, particularly at higher temperatures, is seen to decrease the intensity of the infra-red carbonyl stretching band at 1703 cm-1, but not the one at 1684 cm-1. A model in which two inequivalent sets of TMB molecules in the durene lattice undergo their own unique photochemical and photophysical processes is suggested to explain the results. It is proposed that within each site the lower, predominantly 3ππ* state of the anti TMB conformer is in thermal equilibrium with the higher-lying 3n...

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