Aggregation-Induced Symmetry Breaking from Achiral Systems

Debates on the source of chirality have lasted for several centuries due to its significance for the exploration of the origin of life. It is still a thorny scientific problem that how the first chiral molecule is generated without any chiral factors. In this work, an interesting phenomenon, aggregation-induced symmetry breaking (AISB), is observed in achiral diphenylethylene and p-terphenyl derivatives. For compound (E)-1,2-Bis(2,4,5-trimethylphenyl)ethene (2,4,5-TMe-DPE), there is no chiroptical signal both in its solution and crystal state. However, unexpected chiroptical signals, circular dichroism (CD) and circularly polarized luminescence (CPL), are observed in their aggregate state and the emission dissymmetry factor is as high as 0.015 at 70% water fraction. Meantime, time-dependent CD and CPL effect are also investigated which suggests that AISB involves both dynamic and kinetic processes. Calculation is further carried out to prove the existence of two enantiomers in diphenylethylene and p-terphenyl derivatives. Finally, we propose that the symmetry breaking in aggregate state might be caused by the difference of resolution rate to two enantiomers.