title: Ground and excited states proton transfer reactions of 1,8-diaminonaphthalene in perchloric acid solutions.
abstract: The proton-transfer reaction of 1,8-diaminonaphthalene (1,8-DAN) in acidic medium was studied by means of fluorescence and picosecond spectroscopic techniques. It has been found that there are three different forms of 1,8-DAN in the ground state, but only two different forms in the excited state. The absorption of the mono-cation form of 1,8-DAN is found to be a mixture of the neutral form and the di-cation form. However, the emission is found to be the same as the neutral form, due to the fast dissociation of the mono-cation form once it is excited. The fluorescence of the mono-cation form of 1,8-DAN shows a small shift under different excitation wavelengths. The di-cation form only fluoresces if no free water cluster is available as a proton acceptor. The reaction in the excited state is shown to be a diabatic quenching reaction. With the help of quantum yields and fluorescence lifetime measurements these results are interpreted in terms of a new photochemical scheme. All dissociation and quenching rate constants, pKa and kq, have been determined.
authors.affiliation: Chemistry Department, King Fahd University of Petroleum and Minerals, Dhahran, 31261, Saudi Arabia. abetar@kfupm.edu.sa
authors.forename: Abdul-Rahman
authors.initials: AR
authors.lastname: Al-Betar
authors.forename: Ali
authors.initials: A
authors.lastname: El-Rayyes
authors.forename: Uwe K A
authors.initials: UK
authors.lastname: Klein