A Light Induced Change in Cholesteric Pitch by Photoracemization of a Chiral Pyrenyl Sulfoxide

A cholesteric phase of 4ʹ-pentyl-4-biphenyl carbonitrile (5CB) doped with (R)-(+)"1-pyrenyl-4-toly sulfoxide (1) was observed, Changes in a cholesteric pitch, p, in the liquid crystalline phase was induced by photoracemization and agreed with a theoretical line. A helical twisting power, ? of 1 in 5CB was obtained to be -1,1 mu M(-1) . Anisotropy factor, g, of 1 in acetonitrile was determined to be 2.1 x 10(-3) at 375 nm and 2.9 x 10(-3) at302nm.