A dπ-pπ conjugated system integrating both Hückel rule-violating and rule-compliant aromatic frameworks

Porphyrins have played a time-honored role in chemistry and they continue to attract attention because of their widespread applications. Expanding the range of wavelengths absorbed into the near-infrared (NIR) and increasing the absorption intensity is crucial to improve the photochemical properties of porphyrins. Conventional strategies require dedicated syntheses and are typically characterized by low yields. Additionally, the characteristic energy absorption bands of the resulting porphyrin derivatives exhibit low molar absorption coefficients ( ε ), especially in the NIR-Ⅱ region. Here we show that by introducing an aromatic metallapentalyne that violates Hückel’s rule into a porphyrin system provides a series of porphyrin derivatives exhibiting ultra-strong characteristic absorption bands in the NIR region ( ε > 10 5 M −1 cm −1 ). The approach relies on a reaction between porphyrin alkynyl groups and metal carbynes and enjoys the advantage of facile experimental operation, short synthetic procedures, and broad substrate scope. It also allows the lowest energy absorption band, ascribed to a d π - p π transition, to be tuned to a maximum of 1032 nm with a corresponding narrow optical bandgap of 1.13 eV. The present hybrid materials integrate both Hückel’s rule-violating and rule-compliant aromatic frameworks and display high thermal- and photo- stability, as well as good solubility. Under 1060 nm irradiation a lead system displays a photothermal conversion efficiency (PCE) value of 97%. To our knowledge this represents the highest reported PCE value for a NIR-absorbing dye. It and the other porphyrin metallaaromatic hybrids of this study were found to be promising photothermal therapy agents as inferred from in vivo studies involving tumor-bearing mouse models.