Fluorescence Spectra of 1,1′-Binaphthyl and Related Compounds at High Pressures

Relative to the related compounds 2,2′-binaphthyl (I) and 2,2′-dimethoxy-1,1′-binaphthyl (II), the pressure dependence of the fluorescence of crystals of 1,1′-binaphthyl (III) is complex. Compression to 30 kbar at room temperature shifts the 1La fluorescence spectra of all three compounds to longer wavelength but, for I and II does not change the intensity profile, except for some 0-0 reabsorption. For III, this red shift characteristic of 1La fluorescence spectra is dominated by growth of new bands about 3.5 to 5.0×103 cm−1 to lower energy. Similar new bands are observed when 1,1′-binaphthyl crystals are compressed at 90 K or resolved crystals are compressed at room temperature, but are not found to 30 kbar for dilute solutions of 1,1′-binaphthyl in polyacrylonitrile. The planes of adjacent naphthyl residues along in the crystal are parallel but offset, the normal distance between planes being 3.55 Å; Raman spectra provide no evidence for a structural phase transformation upon compression. These new bands are assigned as the binaphthyl excimer.