Self-Assembled Helical Structures of Pyrene-Conjugated Amino Acids for Near-Infrared Chiroptical Materials and Chiral Photothermal Agents

Materials with chiroptical activity in the near-infrared (NIR) region are emerging candidates for photothermal agents responding to circularly polarized light. However, design, synthesis, and application of organic species with NIR chiroptical activity remain considerable challenges. Here, we present a charge-transfer (CT) strategy to realize chiroptical properties in the NIR region. The NIR chiroptical activity facilitated photothermal performance, which could be tuned by circularly polarized NIR light. The building unit of pyrene-conjugated amino acid derivatives was self-assembled into helical structures with supramolecular tilt chirality in a solid state. The space group and methyl esterification were used to determine helicity parameters and chiroptical properties including circularly polarized luminescence. The CT complexation between pyrene-conjugated amino acid derivatives and the acceptor enabled the absorbance at above 800 nm, inducing the Cotton effects in the NIR-I region with dissymmetry g-factors at 10(-3) magnitude, which were manipulated by the amino acid domains. CT complexes behaved as efficient photothermal agents in both the aqueous and solid phase. Due to the NIR Cotton effects, the heating rate and maximum temperature could be readily controlled and responded to the handedness of circularly polarized light. This work used self-assembled p-conjugated amino acid derivatives and a CT protocol to manipulate the chiroptical activity evolution in the NIR region and realized circularly polarized light-controlled photothermal performances.

Automated summary

The researchers successfully realized chiroptical properties in the near-infrared (NIR) region using a charge-transfer strategy and applied it to photothermal agents. They self-assembled pyrene-conjugated amino acid derivatives into helical structures with supramolecular tilt chirality. By manipulating the amino acid domains, they achieved chiroptical activity evolution in the NIR region and controlled the photothermal performance using circularly polarized NIR light.