Optically detected magnetic resonance spectra of the lowest triplet state of 1-iodonaphthalene in durene at zero and high magnetic fields

This paper describes the results of optically detected magnetic resonance (ODMR) experiments on photoexcited 1-iodonaphthalene (1IN) in a durene host crystal at liquid helium temperatures. The structure observed in both the zero-field (zf) and high-field ODMR transitions is interpreted in terms of a spin Hamiltonian which includes the complete iodine (I=5/2) nuclear quadrupole and hyperfine interactions. Principal values of D (including the absolute signs), P, AI, and estimates of the direction cosine matrices and the components of g are reported. It is concluded from this analysis that (1) the lowest triplet state of 1IN is principally (π,π*) in character but (2) is contaminated by slight admixtures of charge-transfer configurations; (3) the zf parameters of triplet 1IN are considerably perturbed from those of 3B2u naphthalene and presumably reflect the increased importance of second-order spin–orbit contributions to D in the presence of the heavy-atom substituent; and (4) 1IN occupies two magnetically inequivalent sites in the durene lattice which are not substitutional.