Ultrasound-Triggered Heterojunction Helices With Inverted Supramolecular Chirality and Significantly Amplified Circularly Polarized Luminescence.

Abstract

Developing circularly polarized luminescence (CPL) materials with large luminescent dissymmetry factors (glum) through hierarchical self-assembly remains a significant challenge. Herein, we report an ultrasound-triggered hierarchical assembly strategy that enables the construction of heterojunction helices exhibiting inverted supramolecular chirality and substantially amplified CPL. A tetraphenylethylene-alanine derivative forms chiral nanohelices upon heating-cooling in DMSO. The addition of MeCN promotes the growth of nanohelices along with residual monomers into microhelices. Notably, ultrasound following MeCN addition induces reorganization at the termini of the nanohelices, leading to heterojunction helices composed of core and dendritic helical subunits with opposite handedness. These heterojunction helices display inverted and amplified CPL, with a glum value of 0.2 and a fluorescence quantum yield of 50%. Experimental and density functional theory calculations suggest that the ultrasound mechanical force changes the types of hydrogen bonds within extended monomers, thereby redirecting the self-assembly pathway from the ends of nanohelices and newly generated folded monomers. Enhanced interchromophoric interactions and well-ordered dendritic helices contribute to the inversion and amplification of CPL. This study not only presents the first example of heterojunction helices derived from the same chiral molecule but also provides new insights into an ultrasound-triggered pathway for amplifying CPL via hierarchical assembly.