Abstract
Abstract The triplet states (3ππ*) of purine, benzimidazole, and indazole are investigated in benzoic acid crystals by electron paramagnetic resonance (EPR) and optical detection of magnetic resonance (ODMR) techniques. Well resolved phosphorescence spectra were obtained at 4.2 K. The T1 states of purine and benzimidazole are located at 26409 and 26536 cm−1, respectively. The zero field splittings (ZFS) are D=0.1042 cm−1, |E|=0.0608 cm−1 for purine, and D=0.1123 cm−1, |E|=0.0270 cm−1 for benzimidazole. The decay rate constants of the triplet sublevels are determined at 1.5 K and are compared with those of indole. From the angular dependence of the EPR signals, the probable orientations of purine and benzimidazole in benzoic acid hosts are determined. From the observed hyperfine splittings (hfs) spin distribution of the T1 state of purine is estimated. (ρ6=0.20, ρ8=0.27, and ρ2=0.12). The effects of the nitrogen substitution in the pyrole ring of indole on the ZFS and spin distribution are discussed.
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