Fujisawa Jun-Ichi, Kaneko Naohito, Hanaya Minoru
Graduate School of Science and Technology, Gunma University, 1-5-1 Tenjin-cho, Kiryu, Gunma, 376-8515, Japan.
Chem Commun (Camb). 2020 Apr 9;56(29):4090-4093. doi: 10.1039/d0cc00567c.
Interfacial charge-transfer transitions (ICTTs) between organic compounds and inorganic semiconductors have recently gained increasing interest as a new visible light absorption mechanism for optical biosensing via direct visualization, surface enhanced Raman scattering (SERS), and circular dichroism (CD) and also as a direct charge separation mechanism for photoenergy conversions such as photocatalytic reactions. So far, ICTTs have been observed with various organic compounds, while inorganic materials are almost limited to titanium oxides such as TiO2. Although SERS via ICTTs has been reported with several kinds of inorganic semiconductors, their ICTT bands have not been observed directly except for TiO2. From these viewpoints, the direct observation of ICTT bands in inorganic semiconductors other than TiO2 is an important issue. In this study, we demonstrate ICTTs in ZnO induced by the adsorption of aromatic thiols. ICTTs take place from the HOMO of the adsorbed thiol compounds to the conduction band of ZnO via a Ti-S linkage. Notably, ZnO selectively shows ICTTs with aromatic thiols, but almost no ICTT with oxygen-linkage-type organic compounds such as phenol. In addition, the wide-range control of ICTTs was achieved by the chemical modification of aromatic thiols. Our research not only opens up a new way for the research of ICTTs but also supports the reported ICTT-based SERS in ZnO.
有机化合物与无机半导体之间的界面电荷转移跃迁（ICTTs）最近作为一种新的可见光吸收机制受到越来越多的关注，可用于通过直接可视化、表面增强拉曼散射（SERS）和圆二色性（CD）进行光学生物传感，也可作为光催化反应等光能转换的直接电荷分离机制。到目前为止，已在各种有机化合物中观察到ICTTs，而无机材料几乎仅限于二氧化钛（TiO2）等钛氧化物。尽管已报道了通过ICTTs在几种无机半导体上实现SERS，但除TiO2外，尚未直接观察到它们的ICTT带。从这些观点来看，直接观察除TiO2以外的无机半导体中的ICTT带是一个重要问题。在本研究中，我们展示了由芳香硫醇吸附诱导的ZnO中的ICTTs。ICTTs通过Ti-S键从吸附的硫醇化合物的最高占据分子轨道（HOMO）转移到ZnO的导带。值得注意的是，ZnO选择性地与芳香硫醇表现出ICTTs，但与酚等氧键型有机化合物几乎没有ICTTs。此外，通过芳香硫醇的化学修饰实现了ICTTs的大范围调控。我们的研究不仅为ICTTs的研究开辟了一条新途径，也为报道的基于ICTTs的ZnO中的SERS提供了支持。
