Glycyrrhetinic Acid and Polyethylene Glycol-Disubstituted trans/cis-Tetraphenylethene Stereoisomers Showing Thermoresponsive Fluorescent Self-Assembly

Tetraphenylene (TPE)-based stereoisomers have distinct physical, chemical, and stimuli-responsive features, attributed to their geometrical structures. Here, taking advantage of natural glycyrrhetinic acid (GA) with good self-assembly ability and hydrophilic polyethylene glycol (PEG) with thermoresponsive capacity, the amphiphilic trans-/cis-TPE-GA-PEG isomers with aggregation-induced emission (AIE) characteristics are synthesized, which can undergo stereoisomerization under light irradiation. Upon rising water content in tetrahydrofuran/water solution, trans molecules show typical AIE features with formation of nanospheres, while cis isomers display a fluorescence-enhanced property with a red-shift of wavelength and generation of nanovesicles. In addition, both isomers have reversible phase transitions in tetrahydrofuran/water solution, where cis isomers possess a lower phase transition temperature (T_lc) compared with trans-TPE-GA-PEG. During this phase transition process, the morphology of trans and cis isomers transforms from nanospheres into helical fibers and irregular aggregates, respectively, because of the disruption of interactions between PEG chains and water molecules. Our work provides an alternative construction strategy for amphiphilic stimuli-responsive AIE molecules using natural products.