The Influence of Luminophore Orientation and Dynamics on Circularly Polarised Luminescence (CPL) Spectroscopy

Circularly Polarised Luminescence (CPL) spectroscopy often deals with the generation of circularly polarised photons from macroscopically isotropic systems, such as liquid or solid solutions. The magnitude of CPL transitions depends on inherent specific properties of chiral chromophores/luminophores, which is connected to the strength and mutual intra-molecular orientation of the molecular electronic and magnetic transition dipoles. The present work aims to theoretically investigate the influence of orientation and dynamics on CPL emission for luminophores dissolved in microscopic and macroscopic anisotropic systems. Commonly studied systems of this kind are (liquid) crystals, lipid membranes, or model membranes. Typically, they exhibit uniaxial symmetry, and the luminophores considered may undergo fast, intermediate, or negligible reorientations on the timescale of luminescence emission. CPL from anisotropic and isotropic systems have been compared and the obtainable molecular information is described and discussed. Macroscopically isotropic systems, which are simultaneously microscopic anisotropic, are here exemplified by lipid vesicles. Taken together, a fundamental theoretical treatment is presented with connection to various experimental conditions. In brief, different experimental setups and aspects for monitoring the CPL emission are described, as well as commented on.