PROTON TRANSFERS OF AQUEOUS 7-HYDROXYQUINOLINE IN THE FIRST EXCITED SINGLET, LOWEST TRIPLET, AND GROUND-STATES

Proton transfers of aqueous 7-hydroxyquinoline are observed in the lowest tripler states as well as in the first excited singlet and ground states by measuring kinetic profiles and spectra of absorption and emission. An excited normal molecule undergoes within 10 ps protonation to the N atom to form an excited cation intermediate or deprotonation from the OH group to form an excited anion intermediate. The cation's OH group deprotonates in 30 ps while the anion's N atom is protonated in 200 ps, either intermediate yielding a zwitterion as the final photochemical product in the first excited singlet states. Excited zwitterions relax in 3 ns into the lowest tripler state and into the ground state. The ground state reverse proton transfer process is completed in 20 mu s. Triplet state zwitterions go through triplet state proton transfer in 80 mu s, generating cations or anions. The reverse proton transfer triplet state intermediates relax to their ground states in 2 ms, replenishing photon-depleted species immediately without giving birth to transient absorption referable to a cation or anion as ground state proton transfer intermediate. Excitation of zwitterions initiates a proton transfer cycle composed of tripler and ground state proton transfers without excited singlet state proton transfer.