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

Abstract

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 (|g_lum |≈10^-2 ), and quantum yield (Φ_f ≈0.5). Owing to the excellent photophysical properties of the PCDs, the circularly polarized luminescence brightness (B_CPL ) 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.