Excited state proton transfer reactions of 1-naphthylamine (R-NH2) adsorbed at the surfaces of tungstophosphoric acid supported MCM-41 materials have been studied using steady state fluorescence and picosecond time correlated single photon counting techniques. Evidence for the formation of X* (an adduct between the R-NH2 and the acid) showed strongly enhanced surface acidity of the supported MCM-41 materials. The excited state lifetime of X* was used to estimate the surface acidity which was found to be between 9.3 and 10.4 M acidic solution depending upon the solvent used in the loading experiment. (C) 2004 Elsevier B.V. All rights reserved.