Cyclodextrins with Multiple Pyrenyl Groups: An Approach to Organic Molecules Exhibiting Bright Excimer Circularly Polarized Luminescence

We report a simple and effective approach to organic molecules exhibiting bright circularly polarized luminescence (CPL) by combining a chiral cyclic molecular scaffold and multiple excimer-enabling moieties. An α-cyclodextrin (CyD) scaffold was modified with six pyrenyl groups to obtain pyrene-cyclodextrins (PCDs) in a one-step synthesis from commercially available compounds. The PCDs exhibited high molar extinction coefficients (ϵ≈10⁵ M⁻¹ cm⁻¹ ), polarized emission with a good dissymmetry factor (|glum |≈10⁻² ), and quantum yield (Φf ≈0.5). Owing to the excellent photophysical properties of the PCDs, the circularly polarized luminescence brightness (BCPL ) reached 340 M⁻¹ cm⁻¹ . Photophysical and chiroptical studies of the PCDs with only five pyrene units and with linkers of various lengths connecting the CyD with the pyrene units revealed that the formation of a pyrene excimer in a spatially crowded environment is crucial for CPL anisotropy. This study paves the way for the development of bright CPL organic molecules.