THE ISOMERIZATION REACTION OF ELECTRONICALLY EXCITED (DIBENZYLMETHINE) BORONDIFLUORIDE IN N-ALCOHOLS - STUDY OF MICROSCOPIC FRICTION AND POLARITY

Excited state isomerization reaction of a polar and neutral molecule (dibenzylmethine)borondifluoride in solution has been studied using picosecond spectroscopy. The observed isomerization kinetics is clearly non-Kramers type: the hydrodynamic viscosity overestimates the friction experienced by the reaction at high viscosities. Correcting the hydrodynamic friction for relative size effects of the solute and the solvent according to Gierer-Wirtz and Dote-Kivelson-Schwartz results in acceptable well and barrier frequencies but underestimation of the rates at high viscosities remains. Using rotation correlation times as a measure of friction and the Kramers-Hubbard model results in much better agreement between the experiment and theory but an exceedingly high value of barrier frequency is obtained. We believe that frequency dependence of frictional effects is important in isomerization of DBMBF2 in n-alcohols solutions at high values of friction.