Synthesis and chiroptical properties of optically active polymer liquid crystals containing azobenzene chromophores

A series of optically active methacrylic homopolymers, poly[(4-{4'-[(S)-2methyl-1-butyloxycarbonyl]phenylazo)phenoxyl)x-methylene methacrylatel (x = 0, 2, 6, or 11), were synthesized. The structures of the polymers were characterized by IR, H-1 NMR, UV, differential scanning calorimetry, and gel permeation chromatography. The chiroptical properties of the polymers in films were investigated with circular dichroism (CD) measurements. The CD and UV spectra of the films suggested that CD absorptions occurred in the films of the polymers with long spacers (x = 6 or 11) but not in the films of the polymers with short spacers (x = 0 or 2). After irradiation with linearly polarized light at 442 nm, the CD values were amplified in all the polymeric films. The amplificatory values of the CD bands in the absorption region (260-360 nm) of azobenzene chromopbores suggested that the spacer length had an effect on both the transfer of chirality and photoinduced chirality in the polymeric films. The largest level of photoinduced chirality was induced in the polymer containing six methylene units.