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.

Mechanochemical Fabrication of Full-Color Luminescent Materials from Aggregation-Induced Emission Prefluorophores for Information Storage and Encryption

“…The primary challenge involves incorporating functional groups into nonspecialized polymers to produce materials with intense emission characteristics, especially in the solid state. , Overcoming this obstacle could herald new avenues in the design of advanced polymer materials, bridging the divide between mechanoradical methodologies and functional luminescent applications. ,,, Yet, the process of endowing polymers with fluorescence by utilizing mechanophores is met with several challenges, including complex polymerization demands and the widespread issue of aggregation-caused quenching (ACQ), − which markedly dampens emission efficiency when the material is in aggregated or solid states . The advent of aggregation-induced emission (AIE) luminogens has emerged as a beacon of hope, offering a compelling counter to ACQ ones. − AIE luminogens are distinct in that they exhibit intensified emission in the aggregated state, a consequence of restricted intramolecular motions (RIM), , which mitigates nonradiative decay pathways. , Despite the strides made in embedding AIE luminogens into polymer matrices through blending, − copolymerization, − or grafting techniques, − the exploration of their direct integration via mechanoradical coupling for enhanced luminescence remains in its infancy. This can be attributed to the scarcity of appropriately engineered prefluorophores designed for such processes, as well as the absence of effective and optimized coupling strategies.…”