TORSIONAL AND PROTON-TRANSFER DYNAMICS IN SUBSTITUTED 3-HYDROXYFLAVONES

The role of torsional motion in proton transfer dynamics of ,N-dimethy lamino)-alpha-naphthyl-3-hydroxychromone has been studied using time-r esolved emission spectroscopy. Excited state proton transfer (ESPT) ra tes in hydrocarbon solvents of varying viscosities are obtained. The v iscosity is varied so that ESPT rate prior to, and following, torsiona l relaxation may be determined. The results show that as the aryl 'tor sional relaxation proceeds, the exothermicity of proton transfer decre ases and the proton transfer rate increases; thus, the system exhibits ''Marcus inverted'' behavior. These results are interpreted in terms of torsional potentials. These potential energy surfaces are construct ed from solvent-dependent static absorption and emission spectra and t ime-dependent Stokes shift measurements. Potential energy surfaces are constructed for the normal and tautomeric forms af the molecule in bo th torsionally relaxed and unrelaxed states. From these surfaces, a ra tio of reaction rates is obtained, which is in good agreement with exp erimentally determined value.