Synthesis and optical properties of cholesteric liquid-crystalline oligomers displaying reversible thermochromism

ABSTRACT A series of side‐chain liquid crystalline oligomers (P1–P7) have been synthesized with cyclo(methylhydrogeno)siloxane and two cholesteric liquid crystalline monomers cholesteryl 4‐(10‐undecylen‐1‐yloxy)benzoate (M1) and cholesterol 4‐{6‐[(4‐(allyloxyl)‐benzoyl]‐hexanoxocarbonyl}‐benzoate (M2). The chemical structures and liquid crystalline properties of the synthesized oligomers were investigated using various experimental techniques such as FTIR, 1H‐NMR, DSC, POM, and XRD. All monomers and chiral oligomers show a cholesteric mesophase with very wide mesophase temperature ranges. They appear highly thermally stable with decomposition temperatures (Td) at 5% weight loss greater than 300°C. The optical properties of the oligmers have been characterized by reflection spectra and optical rotation analysis. All synthesized oligomers display colors at room temperature, and show reversible thermochromism within a wide temperature range (>120°C). The λmax values of the oligomers also nearly coincide during the first, second, and third heating cycles. The specific rotation of each oligomer is very sensitive to temperature, and the specific rotation value of P3 smoothly changes from −21.7° to −0.7° when it is heated. The optical properties of the oligomers offer tremendous potential for various optical applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1321‐1327, 2013