Mixtures of nematic 4-cyano-4′-pentylbiphenyl and (R)-2,2′-dihydroxy-1,1′-binaphthyl-condensed fulgide derivatives form stable cholesteric liquid crystalline states. Photochromic reactions of them induced the change of their cholesteric pitch reversibly.

When an enantiomer of resolved indolylfulgide (1) or either of the (R)-binaphthol-condensed indolylfulgides (2, 3) was mixed with a nematic liquid crystal (5CB), the cholesteric phase was induced. Their cholesteric pitches were reversibly changed by photoirradiation. Whereas the twisting ability of the cholesteric pitch (βM) was larger for the colorless form than for the colored form in the case of 1, it was larger for the colored form than for the colorless form in the cases of 2 and 3. In addition, βM of 1 is generally smaller than that of 2 and 3. These phenomena were explained in terms of the helical conformation of the hexatriene moiety of fulgides and the chirality of the binaphthol moiety. The cholesteric sense of a fulgide-doped liquid crystal was changed between plus and minus reversibly by the pre-doping of the chiral formaldehyde acetal of 1,1′-bi-2-naphthol ((S)-4).

While the introduction of a methoxy group to C-5 of the indole ring of the indolylfulgide caused a large bathochromic shift of the absorption maximum of its colored form, introduction of a methoxy group to C-6 resulted in enlargement of the molar absorption coefficient of the colored form. The 5,6-dimethoxy-substituted indolylfulgide has both properties.

R)-Binaphthol-condensed benzofurylfulgide 3 was synthesized and its photochromic properties as well as the change in other properties associated with photochromism were investigated. Like its indole analogue 1,3 showed diastereoselective photochromism. Change in CD spectra, odoff switching of fluorescence, and reversible change in pitch length of induced cholesteric liquid crystalline phase, were observed.

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