Picosecond dynamics of conformational changes in 1,1′ binaphthyl

Optically induced conformational changes in 1,1′ binaphthyl in different liquids have been studied on a picosecond time scale with subpicosecond optical pulses from a passively modelocked cw dye laser. The technique used was to measure the risetime of an excited state absorption induced by a 307.5 nm pulse and monitored with a 615 nm probing pulse. The risetime was found to be nonexponential with a 2.5±0.5 psec rapid initial rise followed by a slower component which varied from 11 to 22 psec depending on solvent viscosity. The orientational relaxation of the molecule in its equilibrium excited state configuration was also obtained.