Naphthols with electron-withdrawing groups such as cyano or methanesulfonyl at C-5 and C-8 exhibit greatly enhanced photoacidity. This increase in photoacidity enables the substituted naphthols to undergo excited-state proton transfer (ESPT) in alcohols and Me(2)SO in the absence of water. In aqueous tetrahydrofuran solution, efficient proton transfer to water occurs at much lower water concentrations than with the parent naphthol, and the kinetics of proton transfer indicate that a smaller water cluster is involved.