超分子作用诱导的高效三重态湮灭光子上转换体系的研究

Triplet-triplet annihilation (TTA) based upconversion shows potential applications in photovoltaics and photocatalysis due to its requirement of low excitation power density (solar light is sufficient). Furthermore, TTA upconversion shows strong absorption of excitation light, and readily tunable operational wavelength, etc. However, this newly developed upconversion scheme is facing a few challenges. First, because of the dexter energy transfer, two important steps of the overall process of TTA upconversion is limited by the diffusion-controlled limit rate, (i) the triplet-triplet energy transfer between an energy donor (sensitizer) and an emitting acceptor, and (ii) the bimolecular acceptor triplet-triplet annihilation generating singlet excited state from which the high-energy emission takes place. Hence, the TTA upconversion efficiency is limited. Second, the application of TTA-UC in the ambient aqueous phase has been severely studied because it typically employs organic and metalloorganic chromophores that are soluble only in organic solvents. Therefore, when TTA-UC is employed to enhance the effeciency of the semiconductor photocatalysis, a sensitizer/acceptor pair dissolved in a deoxygenated organic solvent has to be sealed and separated from the aqueous phase, which is nonideal for the most efficient performance. In order to address these fundamental problems of the development of TTA upconversion and for its future application in photocatalysis, photovoltaics, etc. Based on our study on TTA upconversion, herein we will design a general motif in which the sensitizer and the acceptor are connected together by supramolecular interactions in the solution, Thus the previous "intermolecular" TTET (triplet energy transfer from the sensitizer and the acceptor) and TTA (triplet-triplet annihilation between the acceptors) process will be transformed to a more efficient "intramolecular" process. As a result, the TTA efficiency can be improved. Second, we will improve the water solubility of the sensitizer and the acceptor by structure modification as well as by interacting with hydrosoluble supramoleculars. Thus, efficient TTA upconversion in water will be realized. These fundamental investigations will be important for improvement of the TTA upconversion efficiency, as well as for the future applications of the TTA upconversion for luminescent bioimaging, photocatalysis and photovoltaics, etc.

三重态-三重态湮灭（TTA）上转换具有所需激发光强度低(非相干光、太阳光即可)、光敏剂吸光能力强、工作波长可调等优点，在太阳能电池、光催化等领域具有重要的应用前景。目前该领域存在两个主要问题，（1）通过独立优化三重态光敏剂与受体的光物理性质来提高上转换效率受溶液中分子扩散控制极限速率的限制；（2）绝大多数TTA上转换现象只能发生在有机溶液中，限制了TTA上转换在光催化等领域的实际应用。为了解决以上问题，本申请人计划在前期工作的基础上，设计一种基于超分子作用诱导的三重态光敏剂与三重态受体一体化的TTA上转换体系，将传统的光敏剂与受体分子间的三重态能量传递（TTET）及受体分子间的三重态湮灭（TTA）过程转变为更高效的“分子内”的TTET与TTA过程，提高上转换效率；此外，本项目还将对光敏剂与受体进行修饰，提高其水溶性，并利用水溶性超分子主体对二者的高效包结作用，实现水溶液中的高效上转换现象。

三重态-三重态湮灭（TTA）上转换具有所需激发光强度低(非相干光、太阳光即可)、光敏剂吸光能力强、工作波长可调等优点，因其在太阳能电池、光催化、生物成像等领域的重要应用价值而受到广泛关注。TTA上转换的两个重要过程----三重态光敏剂向受体的能量传递（TTET）及受体分子间发生三重态湮灭（TTA）的过程均为Dexter 机制，需要二者能自由运动，并至彼此空间距离在碰撞半径之内才能传递能量，因而其效率受分子扩散的限制。使用超分子包结方法拉近光敏剂与受体的空间距离可望解决这一问题。.在项目资助下，通过化学修饰方法，我们制备了一系列连接了三重态受体的主体分子，并将三重态光敏剂修饰上超分子结合位点，利用主客体相互作用来提高上转换效率。如利用连接了受体的柱芳烃与连接有氰基烷基链作为超分子结合位点的三重态光敏剂之间的主客体相互作用，首次证实了超分子包结可有效提高上转换效率；使用水溶性主体分子实现了水溶液中的上转换。项目积极探索了功能超分子主体的合成与性质研究，合成了第一例具有温度刺激响应手性逆转性质的分子万向节（NUJ）；探索了超分子主体在不对称光化学反应中的应用研究，通过改变外部环境或主体分子结构改变产物分布及手性产物的ee值；项目进一步将三重态光敏剂连接到超分子主体上，实现了TTA上转换敏化的手性光二聚反应，将TTA上转换应用于不对称光化学反应。.通过本项目的研究，建立了利用超分子包结提高TTA上转换效率的新方法，并将TTA上转换的应用范围拓展至不对称光化学反应。.