The Crystalline Nanocluster Phase as a Medium for Structural and Spectroscopic Studies of Light Absorption of Photosensitizer Dyes on Semiconductor Surfaces

The crystalline nanocluster phase, in which nanoscale metal oxide clusters are self-assembled in three-dimensional periodic arrays, is described. The crystalline assembly of nanoparticles functionalized with technologically relevant ligands offers the opportunity to obtain unambiguous structural information that can be combined with theoretical calculations based on the known geometry and used to interpret spectroscopic and other information. A series of Ti/O clusters up to ∼2.0 nm in diameter have been synthesized and functionalized with the adsorbents catechol and isonicotinic acid. Whereas the isonicotinate is always adsorbed in a bridging monodentate mode, four different adsorption modes of catechol have been identified. The particles show a significantly larger variation of the Ti−O distances than observed in the known TiO2 phases and exhibit both sevenfold overcoordination and five- and fourfold undercoordination of the Ti atoms. Theoretical calculations show only a moderate dependence of the catecholate net charge on the geometry of adsorption. All of the catechol-functionalized clusters have a deep-red color due to penetration of the highest occupied catechol levels into the band gap of the Ti/O particles. Spectroscopic measurements of the band gap of the Ti17 cluster are in good agreement with the theoretical values and show a blue shift of ∼0.22 eV relative to those reported for anatase nanoparticles.

本文针对晶体纳米团簇相（crystalline nanocluster phase）展开描述：该相体系中，纳米级金属氧化物团簇通过自组装形成三维周期性阵列。采用与技术应用相关的配体功能化的纳米颗粒晶体组装体，可获取明确的结构信息，此类信息可与基于已知几何结构的理论计算相结合，用于阐释光谱学及其他相关实验数据。研究团队已合成一系列直径约2.0 nm的钛氧（Ti/O）团簇，并采用儿茶酚（catechol）与异烟酸（isonicotinic acid）两种吸附剂对其进行功能化修饰。异烟酸酯始终以桥联单齿模式吸附，而儿茶酚则存在四种不同的吸附模式。该类团簇中钛-氧键长的变化幅度显著大于已知二氧化钛（TiO₂）晶相中的情况，且钛原子同时存在七配位超配位、五配位与四配位低配位的结构特征。理论计算结果表明，儿茶酚盐的净电荷对其吸附几何结构仅存在中等程度的依赖性。所有经儿茶酚功能化修饰的团簇均呈深红色，这源于儿茶酚的最高占据能级渗透进入钛氧团簇的带隙之中。对钛17（Ti₁₇）团簇带隙的光谱测量结果与理论值吻合良好，且相较于锐钛矿（anatase）纳米颗粒的已有报道值，该团簇的带隙出现了约0.22 eV的蓝移。