Aggregation-induced emission enhancement and aggregation-induced circular dichroism of chiral pentaphenylpyrrole derivatives and their helical self-assembly

Abstract

Herein, a pair of enantiomers, (S)-PPPtriAm and (R)-PPPtriAm, with three chiral substituents and their raceme rac-PPPtriAm derived from conjugated luminogen pentaphenylpyrrole were prepared by covalently attaching (R)-/(S)- or racemic 1-phenylethylamine to conjugated 1-biphenyl-2,3,4,5-tetraphenyl pyrrole. The compounds exhibit obvious aggregation-induced emission enhancement (AIEE) features, and the chiral substituents have little effect on the photophysical properties. More importantly, the introduction of chiral substituents endows the chiral compounds (S)-PPPtriAm and (R)-PPPtriAm with distinct aggregation-induced circular dichroism (AICD) with mirror-image Cotton effects and chiral-polarized luminescence (CPL) properties with an emission dissymmetry factor (g_em) in the range of 0.5 × 10⁻³ to 5 × 10⁻³ for (S)-PPPtriAm and −1 × 10⁻³ to −6 × 10⁻³ for (R)-PPPtriAm in a DMSO–water mixture with the water fraction of 40%. The chiral compounds (S)-PPPtriAm and (R)-PPPtriAm can self-assemble into nanofibers, and the lank nanofibers orderly weave and align together to form a regular arrangement of aggregates. The raceme rac-PPPtriAm exhibits AIEE features without any AICD and CPL signals and can self-assemble to form nanoparticle blocks. The enantiomers (S)-PPPtriAm and (R)-PPPtriAm, as AIEE-active luminogens with a multichiral substituent, are expected to have potential applications in photoelectronic materials or in the design of optically active fluorophores for sensitive enantiomer recognition.