Temperature-dependent NIR-CPL spectra of chiral Yb(III) complexes

Chiral, enantiopure Yb(III) complexes are able to emit circularly polarized luminescence (CPL) in the near infrared (NIR) wavelength region, quantified by the dissymmetry factor (glum). Due to crystal field splitting (CFS), the excited state 2F5/2 consists of three mj' sublevels, which are populated in accordance with the Boltzmann distribution. Consequently, room temperature CPL spectra are the sum of various - either positive or negative – contributions, that are practically impossible to quantify. Thanks to the use of an advanced setup enabling CPL measurements over a range of temperatures (300 to 4 K), the interrelation of CFS, glum and temperature was demonstrated on the example of a pair of enantiopure Yb(III) com-plexes. It was thereby confirmed that each mJ’ sublevel gives an independent contribution to the overall CPL spectrum. Hence, the CPL spectra of chiral lanthanide complexes were found to be indeed strongly temperature-dependent, as is the glum dissymmetry factor, as a consequence of the variation in thermal sublevel population. These results were additional-ly interpreted in the framework of multireference wave-function calculations.