Cacciarini Martina, Skov Anders B, Jevric Martyn, Hansen Anne S, Elm Jonas, Kjaergaard Henrik G, Mikkelsen Kurt V, Brøndsted Nielsen Mogens
Department of Chemistry and Center for Exploitation of Solar Energy, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen (Denmark); Department of Chemistry, University of Florence via della Lastruccia 3-13, 50019 Sesto F.no (FI) (Italy).
Chemistry. 2015 May 11;21(20):7454-61. doi: 10.1002/chem.201500100. Epub 2015 Apr 1.
One key challenge in the field of exploitation of solar energy is to store the energy and make it available on demand. One possibility is to use photochromic molecules that undergo light-induced isomerization to metastable isomers. Here we present efforts to develop solar thermal energy storage systems based on the dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch. New DHA derivatives with one electron-withdrawing cyano group at position 1 and one or two phenyl substituents in the five-membered ring were prepared by using different synthetic routes. In particular, a diastereoselective reductive removal of one cyano group from DHAs incorporating two cyano groups at position 1 turned out to be most effective. Quantum chemical calculations reveal that the structural modifications provide two benefits relative to DHAs with two cyano groups at position 1: 1) The DHA-VHF energy difference is increased (i.e., higher energy capacity of metastable VHF isomer); 2) the Gibbs free energy of activation is increased for the energy-releasing VHF to DHA back-reaction. In fact, experimentally, these new derivatives were so reluctant to undergo the back-reaction at room temperature that they practically behaved as DHA to VHF one-way switches. Although lifetimes of years are at first attractive, which offers the ultimate control of energy release, for a real device it must of course be possible to trigger the back-reaction, which calls for further iterations in the future.
太阳能利用领域的一个关键挑战是储存能量并使其按需可用。一种可能性是使用光致变色分子，这些分子会发生光诱导异构化形成亚稳态异构体。在此，我们展示了基于二氢薁（DHA）/乙烯基七富烯（VHF）光/热开关开发太阳能热能存储系统的努力。通过不同的合成路线制备了在1位带有一个吸电子氰基且在五元环中有一个或两个苯基取代基的新型DHA衍生物。特别地，从在1位含有两个氰基的DHA中立体选择性还原去除一个氰基被证明是最有效的。量子化学计算表明，相对于在1位带有两个氰基的DHA，这些结构修饰带来了两个好处：1）DHA - VHF的能量差增大（即亚稳态VHF异构体的能量容量更高）；2）对于能量释放的VHF到DHA的逆反应，活化吉布斯自由能增加。事实上，在实验中，这些新衍生物在室温下极不情愿发生逆反应，以至于它们实际上表现为DHA到VHF的单向开关。虽然数年的寿命起初很有吸引力，这提供了对能量释放的终极控制，但对于一个实际装置而言，当然必须能够触发逆反应，这就需要在未来进行进一步的迭代。
