The self-assembly and chiroptical properties of tetraphenylethylene dicycle tetracholesterol with an AIE effect

摘要

The immobilized propeller-like conformation of tetraphenylethylene (TPE) can be used to emit strong circularly polarized luminescence (CPL) light, but the immobilized propeller-like conformation must be resolved. A single-handed helical conformation of TPE units induced by chiral group(s) that do not need resolution can also enable CPL emission, but related research is very rare. In this paper, TPE dicycle tetracholesterol is synthesized which could self-assemble into nano-tubes with a double molecule-layer shell, and which showed a fluorescence quantum yield of >76%. One film composed of nano-tubes displayed an enhanced first positive circular dichroism (CD) effect and emitted strong positive CPL light. A suspension or solution of the TPE dicycle tetracholesterol in DCE had a first negative CD band and negative CPL emission. In contrast, TPE tetracholesterol without intramolecular cyclization self-assembled into very soft "noodle-like" aggregations and showed very weak CD signals and CPL emission. The TPE dicycle tetracholesterol had a large CPL dissymmetric factor (<= 3.0 x 10(-3)), which was 30 times larger than the TPE tetracholesterol without cycles. Due to the strong bisignate band in the CD spectrum of TPE dicycle tetracholesterol and the absence of a helical structure in aggregates, the CD and CPL signals of the TPE dicycle tetracholesterol could be ascribed to the prevailing single-handed propeller-like conformation of TPE units induced by chiral cholesterol groups.