Department of Chemistry, University of Cincinnati, Cincinnati, Ohio 45221, United States.
J Am Chem Soc. 2023 Feb 15;145(6):3535-3542. doi: 10.1021/jacs.2c12244. Epub 2023 Feb 2.
Homogeneous organic photocatalysis typically requires molecular photosensitizers absorbing in the ultraviolet-visible (UV/vis) region, because UV/vis photons possess the sufficient energy to excite those one-photon-absorbing photosensitizers to the desired excited states. However, UV/vis light irradiation has many potential limitations, especially for large-scale applications, such as low penetration through reaction media, competing absorption by substrates and co-catalysts, and incompatibility with substrates bearing light-sensitive functionalities. In fact, these drawbacks can be effectively avoided if near infrared (NIR) photons can be utilized to drive the target reactions. Herein, we report two benzothiazole-derived compounds as novel two-photon-absorbing (TPA) organic photosensitizers, which can function under NIR light irradiation using inexpensive LED as the light source. We demonstrate that by judicially modulating the donor-π-acceptor-π-donor-conjugated structure containing a bibenzothiazole core and imine bridges, excellent two-photon absorption capability in the NIR region can be achieved, approaching 2000 GM at 850 nm. Together with large quantum yields (∼0.5), these benzothiazole-derived TPA organic photosensitizers exhibit excellent performance in driving various O-involved organic reactions upon irradiation at 850 nm, showing great penetration depth, superior to that upon blue light irradiation. A suite of photophysical and computational studies were performed to shed light on the underlying electronic states responsible for the observed TPA capability. Overall, this work highlights the promise of developing Ru/Ir-free organic photosensitizers operative in the NIR region by taking advantage of the two-photon absorption mechanism.
均相有机光催化通常需要在紫外可见（UV/vis）区域吸收的分子光致敏剂，因为 UV/vis 光子具有足够的能量将那些单光子吸收的光致敏剂激发到所需的激发态。然而，UV/vis 光照射有许多潜在的局限性，特别是对于大规模应用，例如在反应介质中的低穿透率、底物和共催化剂的竞争吸收以及与具有光敏功能的底物不兼容。事实上，如果可以利用近红外（NIR）光子来驱动目标反应，则可以有效地避免这些缺点。在此，我们报告了两种苯并噻唑衍生的化合物作为新型的双光子吸收（TPA）有机光致敏剂，它们可以在近红外光照射下使用廉价的 LED 作为光源工作。我们证明，通过巧妙地调节含有联苯并噻唑核和亚胺桥的供体-π-受体-π-供体共轭结构，可以在近红外区域实现优异的双光子吸收能力，在 850nm 处接近 2000GM。加上高量子产率（约 0.5），这些苯并噻唑衍生的 TPA 有机光致敏剂在 850nm 照射下驱动各种 O 参与的有机反应时表现出优异的性能，显示出很大的穿透深度，优于蓝光照射。进行了一系列光物理和计算研究，以阐明导致观察到的 TPA 能力的潜在电子态。总的来说，这项工作通过利用双光子吸收机制，突出了开发在近红外区域工作的无 Ru/Ir 有机光致敏剂的前景。
