Negative solvatochromism and sign inversion of circularly polarized luminescence in chiral exciplexes as a function of solvent polarity

The potential control of circularly polarized luminescence (CPL), especially its sign and switching at the molecular level without any chemical modification, is desirable, but remains a considerable challenge owing to the difficulty to finely control the magnitude and relative orientation of the associated electric and magnetic dipole transition moments. To address this challenge, we report the synthesis and chiroptical properties of innovative non-conjugated chiral donor-acceptor systems displaying CPL sign inversion as a function of solvent polarity. Through the formation of a chiral exciplex, it is possible to achieve control of its (non-) radiative deexcitation pathways using solvents of different polarity, resulting in emission from locally excited (LE) or charge-transfer (CT) states (with positive and negative CPL), and thermally activated delayed fluorescence (TADF). Theoretical calculations offer further evidence of the relationship between the nature of the emitting species and the CPL. These results provide original molecular design guidelines to obtain switchable CPL emitters, and new insights into the combination of CPL and TADF, a feature of crucial importance for the development of efficient technologies based on CPL emitters.