Department of Chemistry, University of Florence, Via della Lastruccia 3-13, 50019 Sesto Fiorentino, Italy.
Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark.
Molecules. 2021 Oct 26;26(21):6462. doi: 10.3390/molecules26216462.
Photochromic molecules are systems that undergo a photoisomerization to high-energy isomers and are attractive for the storage of solar energy in a closed-energy cycle, for example, in molecular solar thermal energy storage systems. One challenge is to control the discharge time of the high-energy isomer. Here, we show that different substituents in the position of a phenyl ring at C-2 of dihydroazulene (DHA-Ph) significantly increase the half-life of the metastable vinylheptafulvene (VHF-Ph) photoisomer; thus, the energy-releasing VHF-to-DHA back-reaction rises from minutes to days in comparison to the corresponding - and -substituted systems. Systems with two photochromic DHA-Ph units connected by a diacetylene bridge either at the , and positions and corresponding to a linear or to a cross-conjugated pathway between the two photochromes are also presented. Here, the substitution was found to compromise the switching properties. Thus, irradiation of -bridged DHA-DHA resulted in degradation, probably due to the proximity of the different functional groups that can give rise to side-reactions.
光致变色分子是一种经历光异构化到高能异构体的系统，对于在封闭能量循环中储存太阳能很有吸引力，例如在分子太阳能热能存储系统中。一个挑战是控制高能异构体的释放时间。在这里，我们表明二氢吖啶（DHA-Ph）中 C-2 位苯基环上的不同取代基显著增加了亚稳态乙烯庚富烯（VHF-Ph）光异构体的半衰期；因此，与相应的 - 和 - 取代系统相比，释放能量的 VHF 到 DHA 的回反反应从分钟延长到几天。通过二乙炔桥连接两个光致变色 DHA-Ph 单元的系统，无论是在 、 和 位置，并且对应于两个光致变色体之间的线性或交叉共轭途径，也被提出。在这里，发现 取代会损害开关性能。因此，- 桥接的 DHA-DHA 的辐照导致降解，可能是由于不同官能团的接近，这可能导致副反应。
