Modulating planarity of cyanine dye to construct highly stable Haggregates for enhanced photothermal therapy

Self-assembly of dyes has become a flexible strategy to modulate their photophysical properties.H-aggregates show great potential to increase heat generation,while the precise designing of H-aggregates as efficient photothermal agents is still challenging.Herein,a quinoline cyanine(QCy)is developed for constructing stable H-aggregated nanoparticles(NPs)to significantly enhance photostability and photothermal conversion efficiency(PCE).With symmetrical rigid planar quinoline structures,QCy has a small and symmetrical dihedral angle(11.9°),which ensures excellent molecular planarity.In aqueous solution,the planar QCy can form closeπ–πmolecular stacking,and fast self-assemble into stable H-aggregates even at low concentrations(1×10−7 M).QCy H-aggregates are sphere-like NPs(QCy NPs)with an average diameter of 120 nm and exhibit high stability.H-aggregation of QCy significantly enhances PCE from 20.1%(non-H-aggregated QCy)to 63.8%(QCy NPs).In addition,the positive charge of quaternarized quinoline provides mitochondrial anchoring ability,which further enhances the photothermal effect.With high PCE and tumor accumulation,QCy NPs in low-doses have been successfully used in photoacoustic imaging-guided tumor photothermal therapy.