Department of Chemistry, Center for Exploitation of Solar Energy, University of Copenhagen , Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark.
J Org Chem. 2017 Oct 6;82(19):10398-10407. doi: 10.1021/acs.joc.7b01760. Epub 2017 Sep 11.
Efficient energy storage and release are two major challenges of solar energy harvesting technologies. The development of molecular solar thermal systems presents one approach to address these issues by tuning the isomerization reactions of photo/thermoswitches. Here we show that the incorporation of photoswitches into macrocyclic structures is a particularly attractive solution for increasing the storage time. We present the synthesis and properties of a series of macrocycles incorporating two dihydroazulene (DHA) photoswitching subunits, bridged by linkers of varying chain length. Independent of ring size, all macrocycles exhibit stepwise, light-induced, ring-opening reactions (DHA-DHA to DHA-VHF to VHF-VHF; VHF = vinylheptafulvene) with the first DHA undergoing isomerization with a similar efficiency as the uncyclized parent system while the second (DHA-VHF to VHF-VHF) is significantly slower. The energy-releasing, VHF-to-DHA, ring closures also occur in a stepwise manner and are systematically found to proceed slower in the more strained (smaller) cycles, but in all cases with a remarkably slow conversion of the second VHF to DHA. We managed to increase the half-life of the second VHF-to-DHA conversion from 65 to 202 h at room temperature by simply decreasing the ring size. A computational study reveals the smallest macrocycle to have the most energetic VHF-VHF state and hence highest energy density.
高效的能量存储和释放是太阳能收集技术的两大挑战。通过调节光/热致开关的异构化反应，开发分子太阳能热系统提供了一种解决这些问题的方法。在这里，我们展示了将光开关整合到大环结构中是增加存储时间的一种特别有吸引力的解决方案。我们介绍了一系列含有两个二氢吖啶（DHA）光开关单元的大环的合成和性质，这些单元通过不同链长的连接桥连接。与环的大小无关，所有大环都表现出分步、光诱导的开环反应（DHA-DHA 到 DHA-VHF 到 VHF-VHF；VHF = 乙烯庚富烯），第一个 DHA 发生异构化的效率与未环化的母体系统相似，而第二个（DHA-VHF 到 VHF-VHF）则明显较慢。释放能量的 VHF 到 DHA 的环封闭也以分步方式进行，并且在更紧张（较小）的循环中系统地发现其进行得更慢，但在所有情况下，第二个 VHF 到 DHA 的转化率都非常缓慢。通过简单地减小环的大小，我们设法将第二个 VHF 到 DHA 的半衰期从 65 小时增加到 202 小时。计算研究表明，最小的大环具有最具能量的 VHF-VHF 状态，因此具有最高的能量密度。
