LIQUID-CRYSTALLINE POLYMER GELS .3. FACILE AND REVERSIBLE CHOLESTERIC ORDERING OF DYE MOLECULES DOPED IN POLY(GAMMA-BENZYL L-GLUTAMATE) GELS

Azobenzene derivatives carrying alkoxy groups of different lengths were doped in cross-linked gels of poly(gamma-benzyl L-glutamate) (PBLG) that possess cholesteric liquid-crystalline (CLC) order. Azobenzene derivatives with long alkoxy groups showed positive induced circular dichroism (ICD), indicating a preference of parallel orientation to the helix of PBLG. The dye molecules could be doped in and washed out repeatedly. Thus, the CLC gel was shown to provide a facile medium for obtaining an oriented dye system. Azobenzene groups linked to alpha-carbons of a polypeptide chain through a single methylene spacer showed strong preference for perpendicular orientation in the CLC. The most intense ICD was observed when the azobenzene-linked polypeptide was mixed in a CLC that is not cross-linked. The magnitude of the latter ICD was on the same order as the theoretical value calculated assuming a perfect alignment of the helical polypeptides in the CLC.