The unexpected “butterfly effect” of Pt-coordinated cyanine self-assembly for enhanced tumor photothermal therapy

J-aggregates of cyanine have shown great merits in tumor photothermal therapy (PTT) due to their distinct redshift absorption as well as superior photothermal conversion efficiency (PCE). However, due to the complexity of intermolecular interactions, especially the impact of steric hindrance on aggregation, exploring effective strategies to regulate the aggregation modes of organic materials remains challenging. Herein, steric hindrance-regulated J-aggregation of near-infrared (NIR) cyanine was reported based on Pt-coordinated cyanine self-assembly with unexpected “butterfly effect”. Two Pt-coordinated cyanine dimers CyR-Pt (R = Me and Et) were synthesized and spontaneously self-assembled into aggregates in aqueous solution. CyEt-Pt aggregates were loose and amorphous stacking. By replacing ethyl with methyl to reduce steric hindrance, a tiny change resulted in the generation of tightly stacked cyanine J-aggregates (thickness less than 3 nm) observed in CyMe-Pt self-assembly. Significantly, this unexpected “butterfly effect” enabled CyMe-Pt J-aggregates to effectively inhibit reactive oxygen species and greatly improve its photostability. Besides, CyMe-Pt J-aggregates with NIR-II absorption exhibited outstanding photothermal stability and higher PCE (η = 37%) than CyEt-Pt disordered aggregates (η = 20%). Evident tumor suppression performance of CyMe-Pt J-aggregates was validated under 980 nm laser irradiation, demonstrating its great potential in tumor PTT.