COMPARATIVE UV-VISIBLE LUMINESCENCE STUDY OF 1,1'-BINAPHTHYL AND 2,2'-BINAPHTHYL

The modifications of emission spectra obtained in fluid and rigid media as a function of temperature show a conformation change for 1,1'-binaphthyl in the excited state. This change is facilitated in fluid medium by the rotation of the two naphthyl groups around the C1-C1, bond. The molecular twisting in this excited state explains the original results for 1,1'-binaphthyl where the intensity ratio of phosphorescence to fluorescence (I(ph)/I(fluo)) varies with excitation wavelength. This result agrees with the charge transfer (CT) character obtained by the excited state S2* due to the twist of this molecule. The emission spectra of 2,2'-binaphthyl, a molecule which is practically identical in its electronic structure to 1,1'-binaphthyl, do not undergo significant modification with effects of temperature variation, and as a function of the excitation wavelength. These different effects for 1,1'-binaphthyl and 2,2'-binaphthyl agree with the difference of twist for the naphthyl rings around the single bond between these rings.