pH Effect on the efficiency of the photodeactivation pathways of naphazoline: a combined steady state and time resolved study

Abstract

The effect of pH on the spectroscopic behavior of naphazoline [NP, 2-(1-naphthylmethyl)imidazoline] has been examined in aqueous solution by combining steady state and time resolved spectroscopic experiments. The photodeactivation pathways are modulated by the pH changes and can be rationalized on the basis of the chemical structure of the compound. The naphthalene-localized singlet formed upon light excitation is partially deactivated via a reversible energy transfer process involving the imidazoline moiety when NP is present in its cationic form. This process leads to an imidazoline-assisted intersystem crossing being responsible for the population of the lowest naphthalene-localized triplet state.

In the case of the neutral form, the imidazoline ring behaves as an efficient electron donor, which is able to quench the excited naphthalene via a photoinduced electron transfer. Such a process is responsible for the decrease in the naphthalene-localized triplet generation as well as for the reduction of drug photodegradation.