title: Hydroxystilbene isomer-specific photoisomerization versus proton transfer.
abstract: The ground- and excited-state acidities of 3- and 4-hydroxystilbene have been investigated in aqueous solution. Approximate pKa* values determined from the Förster equation are similar for the two isomers; however, 3-hydroxystilbene behaves as a photoacid in water, whereas 4-hydroxystilbene does not. Singular value decomposition with self-modeling is used to obtain more accurate pKa* values for 3-hydroxystilbene. The different behavior of the isomeric hydroxystilbenes is attributed to differences in their excited-state C=C torsional barriers. 3-Hydroxystilbene has a high barrier and a long singlet lifetime, permitting proton transfer to compete with other singlet decay pathways, whereas 4-hydroxystilbene has a low barrier, and thus proton transfer cannot compete with C=C torsion.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113, USA. lewis@chem.northwestern.edu
authors.forename: Frederick D
authors.initials: FD
authors.lastname: Lewis
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Crompton