新型超分子光化学分子器件组装及制氢性能研究

The conversion of solar energy into molecular hydrogen by water splitting has become one of the most important and attractive topics in the field of chemical research. With the aim of improving the efficiency of hydrogen generation, many photochemical molecular devices were constructed by covalently or coordinately linking a photosensitizer and a catalyst. In most reported molecular devices, the photosensitizers in the devices are complexes containing noble metals such Ru, Ir and Pt. These noble-metal complexes are suitable as photosensitizers for photocatalytic hydrogen production from water due to the following several reasons: they show a broad absorption band due to metal-to-ligand charge transfer (MLCT); they have high photostability and appropriate electrochemical properties; the excited states of these complexes have long lifetimes. However, low absorption coefficients in the visible region, the limited availability and high costs of these noble metal-based complexes will become a problem if the field of photocatalytic water splitting find wide application. In the pursuit of more efficient H2-evolving photosensitizers with higher absorption coefficients and better photostability in place of noble metal-based complexes, the proposed research mainly focuses on the boron dipyrromethene (BODIPY) fluorophore by attaching heavy atoms (Br,I) directly onto the chromophore, by making use of the so-called internal heavy-atom effect to generate halogenated BODIPY which will be as kind of excellent and noble-metal-free photosensitizers. These halogenated BODIPY will be further coordinately linked to earth-abundant metal-based catalysts (Co and Ni complexes) to construct absolutely noble-metal-free photochemical molecular devices (PMDs). We will explore the photoinduced H2-evolving efficiency by using these PMDs. The effect of different functional groups and substituted positions on the photophysical properties of the halogenated BODIPY will be investigated. The mechanism of hydrogen production will be also disclosed. The projects from this proposed research will not only benefit from developing new noble-metal-free photochemical molecular devices, but also have the potential to be used in light-driven hydrogen production in homogeneous systems and the development of alternative energy sources to meet the rising global energy demand.

由于传统的钌、铱和铂配合物存在可见光区的摩尔吸光系数低、本身含有来源稀少、成本较高的贵金属成分等缺陷，其作为光解水制氢光敏剂的实际价值和应用均受到了极大的限制。针对这些问题，本项目拟以氟硼吡咯(BODIPY)类有机染料分子为母体，通过引入Br、I等增色基团方式，利用内部重原子效应来实现光跃迁效率的提高，探索合成摩尔吸光系数更高、光稳定性更好的卤代BODIPY系光敏剂来替代传统的贵金属配合物，进一步与Co、Ni等丰产元素催化剂配位连接构筑无贵金属成分的新型超分子光化学分子器件。研究这类分子器件的光驱动水分解制氢效率，探索官能团种类、位置变化对光敏剂的光物理性能的影响；研究分子器件与光解水制氢的构效关系，阐明相关制氢机理，从而为研制无贵金属成分的新型光解水制氢分子器件开辟一条崭新的途径，这对于发展均相光催化分解水制氢新技术、绿色新能源领域探索具有重要的科学意义。

具有光致制氢功能的超分子光化学分子器件的组装及性能研究目前已经取得一定进展，各种组装策略及基于过渡金属配合物特别是贵金属配合物为光敏剂的使用多已见文献，但是以卤代氟硼吡咯(BODIPY)有机染料为光敏剂单元所构筑的光化学分子器件及其制氢性能研究还是非常少见，并且我们在前期也取得了一些研究成果。在本项目执行期内，我们重点合成并单晶结构表征了一系列含Br、I等卤素重原子增色基团所修饰的BODIPY有机光敏剂，探索光敏剂的光物化性能和敏化性质。进一步与钴肟配合物催化剂通过金属-N键配位连接构筑一系列新型超分子光化学分子器件。探索了这类分子器件的制氢效率，官能团种类、位置变化对光敏剂的光物理性能的影响；从实验及理论方面阐述了分子器件与制氢性能之间的构效关系及相关制氢机理。研究结果对发展光制制氢功能的分子器件和功能材料化学、绿色新能源领域探索具有重要的学术意义。