Optical, Electric and Magnetic Properties of Molecules: Scientific Review of A.D. Buckingham's Work | Molecular Physics Research & Applications

Not mentioned in this book is the work that David and I ( as a Nato postdoc in 1969) did to measure the optical activity of water and other oriented molecules! While the average of optical activity tensor diagonal components of H2O is zero as every chemist knows, the off diagonal components are not. I had shown the year before at Cal Tech that it was possible to measure optical dichroism of molecules oriented in nematic liquid crystals. So our strategy for measuring the anisotropy of the optical activity tensor was to orient an optically active molecule in an aligned nematic liquid crystal host.As every chemist knows, optically active molecules have a twist to them. To our surprise the twist in guest molecule caused the nematic host molecules also to twist from their aligned uniaxial state to a twisted nematic phase i.e. what is called a cholesteric phase. This prevented us from measuring the anisotropy of the optical activity tensor. We reported this interesting phase change in Chem Phys Letters in 1969. This observation has had important practical outcomes for liquid crystal displays in that twisted nematics are used in today's displays!