Dependence of the triplet state properties on the orientation of metal ion perturbers in naphthalene-crown ether metal ion complexes. I. External heavy atom effect

The lowest excited triplet state and the sublevel dynamics have been studied in 1, 5-naphtho-22-crown-6 (I), 1,8-naphtho-21-crown-6 (II), and 2, 3-naphtho-20-crown-6 (III) and their complexes with various metal ions (Na+, K+,Cs+, Tl+) using optical detection of magnetic resonance at 1.2 K in zero applied magnetic field. The results indicate that the orientation of the heavy ion perturber with respect to the naphthalene chromophore selectively influences both the sublevel radiative rates and their populating rates by intersystem crossing. The largest heavy atom effect results when the metal ion perturber is located along the out-of-plane axis originating from the center of the naphthalene chromophore (I). The selective effects on the sublevel dynamics can be explained in terms of symmetry restrictions which enter the spin–orbit matrix elements via overlap integrals between the pi electrons of naphthalene and the p orbitals of the heavy atom.