Chiral Pentaphenylpyrrole Derivatives with Aggregation-Induced Emission Enhancement and Aggregation Induced Circular Dichroism and Their Helical Self-assembly

Abstract

A pair of enantiomers (S)-P5PdiAM and (R)-P5PdiAM containing two chiral substituents, and their raceme rac-P5PdiAM were synthesized by introducing (R)-/(S)- or racemic 1-phenylethylamine into 1-biphenyl-2,3,4,5-tetraphenylpyrrole. The target compounds all show weak aggregation-induced emission enhancement (AIEE) characteristics in the DMSO/H2O mixed system, indicating that the introduction of chirality hardly affect the photophysical properties of the compound. In addition, the chiral compounds (S)-P5PdiAM and (R)-P5PdiAM show strong circular dichroism (CD) signals in THF/H2O mixed solution with a water fraction of 70%, that is, they exhibit aggregation-induced circular dichroism characteristics (AICD). Because the aggregates of (S)-P5PdiAM and (R)-P5PdiAM emit weakly, there is no circularly polarized luminescence (CPL) signals upon aggregation. The chiral compounds (S)-P5PdiAM and (R)-P5PdiAM can self-assemble to form helical nanofibers in a THF/H2O mixture with a water fraction of 70%, while the racemic rac-P5PdiAM assembled to form nano-particles, indicating that chiral substituents have a great influence on the self-assembly and the morphologies of the nano-aggregates.