THE EFFECT OF INTRAMOLECULAR TWISTING ON THE EMISSION SPECTRA OF HINDERED AROMATIC MOLECULES: PART I. 1,1′-BINAPHTHYL

Abstract

The fluorescence spectrum of 1,1′-binaphthyl has been examined in solution, in rigid glass, and in the crystal. It is found that in rigid media the spectral location of the emission is very sensitive to temperature. At 300 °K the band is broad and structureless with a maximum at 26,700 cm−1 and a zero–zero band at about 30,200 cm−1 with very low intensity. The same is true at 273 °K and 195 °K. At temperatures below 157 °K structure starts to appear until at 77 °K the center of gravity of the emission is around 29,000 cm−1 and the 0–0 band at 31,270 cm−1 is quite clear and strong. Even at 77 °K there is apparent a broad, but now weak band at 27,260 cm−1. In the crystal the spectrum is broad and structureless at 300 °K with a maximum emission intensity at 26,300 cm−1. On lowering the temperature to about 142 °K the intensity is built up on the high energy side of this band until eventually a new peak at 27,850 cm−1 becomes apparent at 77 °K.These results are interpreted on the basis of unsymmetrical potential energy variations with angle of twist which permit two origins for the fluorescence spectra of double molecules of this type.