Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Abstract

Aggregation plays a critical role in modulating the photophysical process of organic molecules. However, rational control of the construction of a function-oriented stacking mode for efficient photothermal conversion in the second near-infrared region (NIR-II, 1000-1700 nm) remains a challenge. Herein, an H-aggregation of 3,3',5,5'-Tetramethylbenzidine (TMB)-TMB dication (TMB ++ ) complexes in linear agarose (H-TTC/LAG) with narrowed band gap (0.96 eV) is fabricated through intermolecular hydrogen bonding interactions between the amino groups of TTC and the peripheral hydroxyl groups of linear agarose. Charge transfer mechanism and Haggregation ensure the NIR-II absorption (over 1400 nm), and H-aggregation also promotes the non-radiation relaxation pathway and improves the thermal stability of TTC, which together gift the constructed H-TTC/LAG with ultra-efficient photothermal conversion that can quickly increase by 140 °C in 15 seconds under the NIR-II laser (1064 nm, 1.0 W cm -2 ) irradiation. Such unique H-TTC/LAG with good biocompatibility is used for photothermal therapy and demonstrates superior tumor growth inhibition efficiency. This is the H-aggregation of charge transfer complexes in a noncovalent system, which not only provides a new strategy to develop ultra-

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“…[28][29][30][31][32][33][34][35][36][37][38][39] Yet, transporting NIR light energy into subcutaneous tissues with a depth over 1.0 cm remains a challenge. [40][41][42][43][44][45] It is because that the loss of light energy also appears to be inevitable in NIR window due to the intrinsic light absorption and light scattering by skin tissues. In regard to this aspect, the future PTT calls for emergent development toward becoming effective in deep-sited tumor treatment under a light power density safe to skin tissues.…”

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