TY - JOUR
T1 - Photoswitchable Dihydroazulene Macrocycles for Solar Energy Storage
T2 - The Effects of Ring Strain
AU - Vlasceanu, Alexandru
AU - Frandsen, Benjamin N.
AU - Skov, Anders Bo
AU - Hansen, Anne Schou
AU - Rasmussen, Mads Georg
AU - Kjærgaard, Henrik Grum
AU - Mikkelsen, Kurt Valentin
AU - Nielsen, Mogens Brøndsted
PY - 2017/10/6
Y1 - 2017/10/6
N2 - 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 DHAVHF 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.
AB - 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 DHAVHF 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.
U2 - 10.1021/acs.joc.7b01760
DO - 10.1021/acs.joc.7b01760
M3 - Journal article
C2 - 28853882
SN - 0022-3263
VL - 82
SP - 10398
EP - 10407
JO - The Journal of Organic Chemistry
JF - The Journal of Organic Chemistry
IS - 19
ER -