Synthesis, Structure, and Excimer Formation of Aromatic Cholesteric Liquid Crystals

Article abstract of DOI:10.1021/j150657a045

Cholesteryl ο-arylalkanoates having phenyl, 1-naphthyl, and 1-pyrenyl groups as aromatic groups were synthesized, and some of those were found to form the cholesteric liquid crystal (CLC) phase.The pitch and the screw sense of the helix were determined from the selective reflection wavelength and the circular dichroism.The pitch was around 800 nm for cholesteryl 5-(1-naphthyl)pentanoate and about 970 nm for cholesteryl 3-(1-naphthyl)propionate.The helix sense was left-handed for all cholesteryl esters which form the CLC phase.The orientation of naphthyl groups within each quasi-nematic layer was qualitatively discussed from the sign of cirular dichroism at the ¹L_a absorption band.The short axis of the 1-naphthyl group was parallel to the optical or the molecular axis of the quasi-nematic layer in the CLC of cholesteryl 1-naphthylpropionate and -pentanoate, whereas the short axis of 2-naphthyl group was perpendicular to the optical axis of the CLC of cholesteryl 2-naphthylpropionate.The orientation of the excimer transition moment was investigated by circularly polarized fluorescence spectroscopy.The transition moments for all chromophoric CLC's were found to be nearly perpendicular to the optical axis.From these spectroscopic data, an intralayer excimer configuration for 1- and 2-naphthyl groups was proposed.In the mixture of cholesteryl 3-(1-pyrenyl)propionate (60 molpercent) and 3-phenylpropionate (40 mol percent), the excimer formation was more efficient in the CLC phase than in the crystalline phase.