Investigation of Excited-State Proton Transfer in 2-Naphthol Derivatives Included in Langmuir−Blodgett Films

The excited-state proton transfer in LB films of 2-naphthol-6-sulfonamide of dodecylamine (NSDA) has been studied by spectrofluorimetric methods. A modification of the composition of the atmosphere surrounding the samples enables an identification of emission peaks of the reactants, namely, an excited protonated (ROH*) form and a dissociated (RO-*) form taking part in the excited-state deprotonation (ESDP). The mechanism of proton transfer and the nature of the proton acceptor were assessed from the study of separated emission spectra, taken at various experimental conditions and for various film layouts. The estimated rate of proton transfer was between 5 × 108 and 5 × 109 s-1. The results concerning ESDP in LB films suggest that water molecules, probably forming chains of hydrogen bonds (“proton wires”), and carboxyl groups forming a type of hydrogen bonds with a proton donor could be the main proton acceptors.