Circularly polarized luminescence from a common alkoxy pillar[5]arene and its co-aggregates with π-conjugated rods

Abstract

Cylinder-shaped macrocycles composed of π-panels have attracted special attention as one of the best platforms for the development of organic molecule-based chiroptical materials. Pillar[n]arenes are a class of macrocycles with the advantage of easy preparation but have not been extensively investigated from the perspective of luminescent molecules. However, common alkoxy pillar[n]arenes are fluorescent in non-haloalkane solvents, showing potential to be used for molecule-based chiroptical materials. In this work, circularly polarized luminescence (CPL) spectra are reported for a pillar[5]arene with stable planar chirality using tetrahydrofuran (THF) and cyclohexane as solvents, which has been missing for many years. The pillar[5]arene also forms co-aggregates with 1,4-bis(phenylethynyl)benzene and 1,4-bis[(pentafluorophenyl)ethynyl]benzene in THF/H₂O mixtures, owing to a hydrophobic effect. The co-aggregates with the fluorinated π-rod display a new low-energy absorption peak and broad emission band as well as intense circular dichroism and CPL signals. Chiral information from the enantiopure pillar[5]arene core is efficiently transmitted to the co-aggregates with the π-conjugated rod, leading to the highest dissymmetry factor for CPL (2.9 × 10⁻² at 472 nm) among pillar[n]arene-based CPL materials.