Tartaric acid-based chiral polyamides: unraveling intrinsic multicolor clusteroluminescence and the solvent-modulated emission mechanism

Abstract

Non-traditional intrinsic luminescent polymers (NTILPs) have shown great potential in bioimaging and anti-counterfeiting applications. However, the intrinsic luminescence mechanism in these polymers is still under debate, with clustering-triggered emission (CTE) theory being one of the most plausible explanations; yet, further research is needed. In this work, starting from acylamination of tartaric acid, we synthesized a pair of chiral polyamides, PA6LAT and PA6DAT. Circular dichroism spectroscopy confirmed the opposite helical conformations of PA6LAT and PA6DAT, exhibiting pronounced aggregation chirality amplification behavior and demonstrating typical CTE characteristics. The solid-state powders of the polyamides showed finely tunable multicolor fluorescence under different excitation wavelengths. The presence of through-space conjugations in the polyamides was further confirmed through theoretical calculations, revealing the significance of amide clusters and oxygen clusters in their CTE behavior. Interestingly, changing the solvent from HFIP to DMSO enabled single emission behavior in polyamide solutions, with the emission peak precisely tunable from 430 nm to 485 nm. This solvent-dependent shift was attributed to the differential dissociation of amide and oxygen clusters in these two solvents, corresponding to the opposite optical rotation of the polyamides induced by solvents. The fluorescence behavior in solvents also further confirmed the emission mechanism triggered by amide and oxygen clusters in PA6LAT and PA6DAT. This study deepened the understanding of the intrinsic luminescence mechanism of polyamides, reporting for the first time the precise tuning of the fluorescence behavior of NTILPs and the underlying mechanism through solvent-induced effects, contributing to a better understanding of the multicolor luminescence behavior of NTILPs.