Stokes Spectropolarimetry Applied to Measure Circular Birefringence Dispersion of Aqueous Solutions of Sugars

Circular birefringence (CB) is defined as the difference in refractive index for opposite circular polarization states and has played a crucial role in the development of stereochemistry and the concept of chirality. It manifests experimentally as optical rotatory dispersion (ORD), that is, the wavelength-dependent optical rotation of the plane of light polarization. However, most methods for probing ORD rely on analyzing transmitted light asymmetry at single wavelengths (usually the sodium D-line at 589 nm) with linear polarizers, which cannot discern between unpolarized and circularly polarized light, limiting the apparatus to analyze a single phenomenon. Here we showcase the use of Stokes spectropolarimetry (SSP), a versatile and cost-effective technique, to probe ORD of circularly birefringent materials. This technique allows complete analysis of the dispersive changes in polarization caused by anisotropic media, portraying a versatile experimental framework to study different types of optical anisotropies with a single spectropolarimeter. Here, aqueous solutions of chiral sucrose, fructose, and their mixtures are investigated. The ORD acquired verify that the optical rotation is proportional to the concentration of the chiral species and follows an inverse proportion with wavelength. As a case study, we show via SSP that ORD at 589 nm (D-line of sodium) is in good agreement with literature (+63.5° ± 1.4° mL g^-1 dm^-1 for sucrose and -83.7° ± 2.0° mL g^-1 dm^-1 for fructose).