Fujisawa Jun-ichi, Nagata Morio, Hanaya Minoru
Graduate School of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma 376-8515, Japan.
Phys Chem Chem Phys. 2015 Nov 7;17(41):27343-56. doi: 10.1039/c5cp04456a.
A novel group of organic-inorganic hybrid materials is created by the combination of titanium dioxide (TiO2) nanoparticles with bis(dicyanomethylene) (TCNX) electron acceptors. The TiO2-TCNX complex is produced by the nucleophilic addition reaction between a hydroxy group on the TiO2 surface and TCNX, with the formation of a σ-bond between them. The nucleophilic addition reaction generates a negatively-charged diamagnetic TCNX adsorbate that serves as an electron donor. The σ-bonded complex characteristically shows visible-light absorption due to interfacial charge-transfer (ICT) transitions. In this paper, we report on another kind of complex formation between TiO2 and TCNX. We have systematically studied the structures and visible-light absorption properties of the TiO2-TCNX complexes, with changing the electron affinity of TCNX. We found that TCNX acceptors with lower electron affinities form charge-transfer complexes with TiO2 without the σ-bond formation. The charge-transfer complexes show strong visible-light absorption due to interfacial electronic transitions with little charge-transfer nature, which are different from the ICT transitions in the σ-bond complexes. The charge-transfer complexes induce efficient light-to-current conversions due to the interfacial electronic transitions, revealing the high potential for applications to light-energy conversions. Furthermore, we demonstrate that the formation of the two kinds of complexes is selectively controlled by the electron affinity of TCNX.
通过将二氧化钛（TiO₂）纳米颗粒与双（二氰基亚甲基）（TCNX）电子受体相结合，创造出了一类新型的有机-无机杂化材料。TiO₂-TCNX络合物是由TiO₂表面的羟基与TCNX之间的亲核加成反应产生的，它们之间形成了一个σ键。亲核加成反应产生了一种带负电荷的抗磁性TCNX吸附质，它作为电子供体。这种σ键合络合物由于界面电荷转移（ICT）跃迁而具有特征性的可见光吸收。在本文中，我们报道了TiO₂与TCNX之间的另一种络合物形成。我们系统地研究了TiO₂-TCNX络合物的结构和可见光吸收特性，同时改变了TCNX的电子亲和力。我们发现，电子亲和力较低的TCNX受体与TiO₂形成电荷转移络合物，且不形成σ键。这种电荷转移络合物由于几乎没有电荷转移性质的界面电子跃迁而表现出强烈的可见光吸收，这与σ键络合物中的ICT跃迁不同。由于界面电子跃迁，电荷转移络合物能诱导高效的光电流转换，显示出在光能转换应用方面的巨大潜力。此外，我们证明了这两种络合物的形成是由TCNX的电子亲和力选择性控制的。
