Excited-state dynamics in 8-hydroxyquinoline dimers

Electronic excitation of the 8-hydroxyquinoline dimer in cyclohexane induces a transient electronic absorption at wavelengths from 400 to 530 nm with a 1.7±0.2-ps single exponential decay. The similarity between 8-hydroxyquinoline and 7-azaindole, a widely studied excited-state proton transfer system, suggests that the decay reflects the excited-state proton transfer. Measurements on the deuterated dimer show no kinetic isotope effect, which is consistent with previous studies concluding that the proton transfer in 8-hydroxyquinoline is barrierless. These results suggest that excited-state proton transfer takes only a few picoseconds in 8-hydroxyquinoline dimers.