-benzoxazole: two photostabilizers that undergo excited-state proton transfer

Electroabsorption is used to determine the difference dipole moment, NDmN , and the difference polarizability, Da , of Ž . HBT and HBO, two molecules that undergo excited-state intramolecular proton transfer ESIPT . These measurements are Ž ). Ž . compared to ab initio 6-31G and semi-empirical INDO1rs calculations. Good agreement is obtained between ab initio and experimental NDmN values. However, the negative Da values obtained experimentally for both molecules are in disagreement with the calculated Da values which are positive. The absorption maxima, measured as a function of solvent polarity, support the electroabsorption results. Agreement between the observed and calulated shift requires that Da for both molecules be negative. q 1998 Elsevier Science B.V. All rights reserved.