EXCITED-STATE PROTON-TRANSFER IN 1-NAPHTHOL-CENTER-DOT(NH3)(N) COMPLEXES - THE THRESHOLD SIZE IS N = 4

Resonant two-photon ionization, fluorescence and fluorescence-detected excitation spectra of l-naphthol(NH,),, clusters are reported and int erpreted with emphasis on determining the smallest clusters for which excited-state proton transfer (ESPT) can occur. Consistent with the ea rliest studies but in contrast to more recent work, the ESPT threshold is found at n = 4, not n = 3. The confusion is shown to have arisen f rom weak, broad fluorescence of n = 1-3 clusters extending to similar to 400 nm. Excitation spectra of genuine ESPT emission at longer wavel engths gives no indication of contributions from n < 4. (C) 1998 Elsev ier Science B.V. All rights reserved.