Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
J Am Chem Soc. 2014 Aug 6;136(31):11057-64. doi: 10.1021/ja5049412. Epub 2014 Jul 28.
The energy stored in the triplet states of organic molecules, capable of energy transfer via an emissive process (phosphorescence) or a nonemissive process (triplet-triplet transfer), is actively dissipated in the presence of molecular oxygen. The reason is that photoexcited singlet oxygen is highly reactive, so the photoactive molecules in the system are quickly oxidized. Oxidation leads to further loss of efficiency and various undesirable side effects. In this work we have developed a structurally diverse library of hyperbranched unsaturated poly(phosphoester)s that allow efficient scavenging of singlet oxygen, but do not react with molecular oxygen in the ground state, i.e., triplet state. The triplet-triplet annihilation photon upconversion was chosen as a highly oxygen-sensitive process as proof for a long-term protection against singlet oxygen quenching, with comparable efficiencies of the photon upconversion under ambient conditions as in an oxygen-free environment in several unsaturated polyphosphates. The experimental results are further correlated to NMR spectroscopy and theoretical calculations evidencing the importance of the phosphate center. These results open a technological window toward efficient solar cells but also for sustainable solar upconversion devices, harvesting a broad-band sunlight excitation spectrum.
在存在分子氧的情况下，有机分子三重态中储存的能量可通过发射过程（磷光）或非发射过程（三重态-三重态转移）进行能量转移，这种能量会被积极耗散。原因是光激发的单线态氧具有很高的反应性，因此系统中的光活性分子会迅速被氧化。氧化会导致效率进一步降低，并产生各种不良的副作用。在这项工作中，我们开发了一个结构多样的超支化不饱和聚（膦酸酯）库，这些聚合物可以有效地清除单线态氧，但不会与基态（即三重态）的分子氧反应。选择三重态-三重态湮灭光子上转换作为一种对氧非常敏感的过程，以证明对单线态氧猝灭的长期保护，在几种不饱和聚磷酸酯中，在环境条件下和无氧环境下，光子上转换的效率相当。实验结果进一步与 NMR 光谱和理论计算相关联，证明了磷酸酯中心的重要性。这些结果为高效太阳能电池以及可持续太阳能上转换器件开辟了技术窗口，可利用宽带太阳光激发光谱。
