Chiroptical spectrophotometer and analytical method for optically anisotropic samples.

Abstract

A new dual-polarization-modulated comprehensive chiroptical spectrophotometer (D-CCS) was successfully developed for recording artifact-free chiroptical circular dichroism (CD) and circularly polarized luminescence (CPL) spectra of optically anisotropic samples on the basis of the Stokes-Mueller matrix approach. The D-CCS includes an additional second photoelastic modulator (PEM) set in front of the sample and a second PEM controller being driven independently of the first PEM driver, which are essential for obtaining artifact-free chiroptical signals of optically anisotropic samples containing non-chiral signals, i.e., linear birefringence, linear dichroism, and linearly polarized luminescence. The theory and implementation of the method are described, and examples of its application to CD and CPL samples with macroscopic anisotropies are provided. An important advantage of the developed D-CCS is that it reduces the essential step of sample rotation in the plane, including the gravitational axis, to obtain artifact-free CD signals. Consequently, this dual-polarization method shortens the time required to obtain artifact-free CD signals by half and could be very effective for samples, such as high fluidity samples, gels, liquid crystals, and supramolecules in solution, for which artifact-free chiroptical signals are difficult to obtain using conventional methods.