Five-Order-of-Magnitude Reduction of the Triplet Lifetimes of N-Heterocycles by Complexation to a Trinuclear Mercury Complex

The complexation of N-methylcarbazole and N-methylindole by trimeric perfluoro-o-phenylene mercury (1), which can be readily observed in CH2Cl2 solution, leads to the formation of [1.N-methylindole] (2) and [1.N-methylcarbazole] (3) as solid adducts. The solid-state photoluminescence spectra of these adducts show intense emission bands attributed to monomer phosphorescence of N-methylindole and N-methylcarbazole, respectively, with microsecond lifetimes. Remarkably, the triplet lifetimes of the heterocycles in 2 and 3 are shortened by 5 orders of magnitude when compared to those of the free heterocycles. These results are rationalized by invoking the combined external and internal spin-orbit coupling perturbation provided by the mercury and nitrogen atoms.