Molecular Biophysics and Integrated Bioimaging Division and ‡Joint Center for Artificial Photosynthesis, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, University of California , Berkeley, California 94720, United States.
J Am Chem Soc. 2017 Apr 19;139(15):5458-5466. doi: 10.1021/jacs.7b01070. Epub 2017 Apr 6.
The mechanism of visible light-induced hole transfer from a molecular light absorber, in the form of a free-base porphyrin, coupled to a CoO nanoparticle catalyst for water oxidation by a molecular wire (p-oligo(phenylenevinylene) featuring three aryl units) is investigated by transient absorption spectroscopy. The wires are covalently anchored on the CoO surface and embedded in a dense, yet ultrathin (2 nm), silica layer that separates light absorber and catalyst. The porphyrin is electrostatically adsorbed on the silica surface, and aqueous colloidal solutions of the core-shell particles are used for transient optical measurements. Pulsed optical excitation of the porphyrin results in rapid injection of the photogenerated hole onto the molecular wire and concurrent formation of reduced light absorber in less than 1 picosecond (ps). Ultrafast charge separation was monitored by transient absorption of the wire radical cation, which is given by bands in the 500 to 600 nm region and at 1130 nm, while formation of reduced porphyrin was characterized by absorption at 700 nm. Forward transfer of the hole to CoO catalyst proceeds in 255 ± 23 ps. Ultrafast transfer of positive charge from the molecular assembly to a metal oxide nanoparticle catalyst for water oxidation is unprecedented. Holes on CoO recombined with electrons of the reduced sensitizer with biphasic kinetics on a much longer time scale of ten to several hundred nanoseconds. The unusually efficient hole transfer coupling of a molecular light absorber with an Earth-abundant metal oxide catalyst by silica-embedded p-oligo(phenylenevinylene) offers an approach for integrated artificial photosystems featuring product separation on the nanoscale.
通过瞬态吸收光谱研究了以自由碱基卟啉的形式存在的分子光吸收体与 CoO 纳米粒子催化剂之间的可见光诱导空穴转移机制，该催化剂通过分子导线（具有三个芳基单元的 p-聚（亚苯基乙烯基））进行水氧化。这些导线通过共价键固定在 CoO 表面，并嵌入在将光吸收体和催化剂隔开的致密、超薄（2nm）的二氧化硅层中。卟啉通过静电吸附在二氧化硅表面上，使用核壳粒子的水胶体溶液进行瞬态光学测量。卟啉的脉冲光激发导致光生空穴快速注入分子导线上，并在不到 1 皮秒（ps）的时间内同时形成还原光吸收体。通过导线自由基阳离子的瞬态吸收监测超快电荷分离，该阳离子在 500 到 600nm 区域和 1130nm 处给出了带，而还原卟啉的形成则通过 700nm 处的吸收来表征。空穴向前转移到 CoO 催化剂需要 255±23ps。将正电荷从分子组装体超快转移到用于水氧化的金属氧化物纳米粒子催化剂是前所未有的。在更长的 10 到数百纳秒的时间尺度上，CoO 上的空穴与还原敏化剂的电子以两相动力学重新结合。通过嵌入二氧化硅的 p-聚（亚苯基乙烯基）将分子光吸收体与地球丰富的金属氧化物催化剂进行高效空穴转移偶联，为具有纳米尺度产物分离的集成人工光合作用系统提供了一种方法。
