Abstract:Photosensitized isomerization of norbornadiene to quadricyclene was investigated by using several photosensitizers such as toluene, acetone, acetophenone, benzophenone and a-naphthoquinone. The effect of wavelength on the quantum yield of quadricyclene and on the energy conversion efficiency was measured by using spectroirradiator. The formation of byproduct polymer in the presence of photosensitizers was also studied. The formation of polymers during irradiation, which prevents the repeated use of energy stor… Show more
“…These benefits are to some extent hampered by the fact that the parent NBD does not absorb light above 267 nm [10] . Therefore, a triplet photosensitizer is necessary to facilitate the light‐induced isomerization of unsubstituted NBD to the energy‐rich QC [8a, 25] . During this work, we opted to utilize acetophenone as a photosensitizer.…”
Cobalt catalysts are immobilized on the surface of iron oxide nanoparticles for the preparation of highly active quasi‐homogeneous catalysts toward an efficient release of photochemically stored energy in norbornadiene‐based photoswitches. The facile separation of the iron oxide nanoparticles through exploitation of the intrinsic magnetic properties of this material enables efficient cyclization of energy storage and release. Through the transition from cobalt (II) salphen to cobalt porphyrins, a 22.6‐fold increase in the catalytic efficiency of the QC‐NBD back‐conversion is achieved, with an initial TOF of up to 3.64 s−1 and excellent TON of over 3305. In addition, a series of novel “push–pull” functionalized norbornadiene derivatives is prepared, featuring excellent absorption properties with maxima up to 366 nm, quantum yields around 70 %, high energy storage capacities of up to 98.0 kJ mol−1, and outstanding thermal stability with t1/2 (25 °C) over 100 days. Finally, the energy storage potential of these molecular solar thermal (MOST) systems is harnessed in a heat release experiment. This demonstrates the potential of norbornadiene‐based photoswitches in combination with efficient magnetic catalysts for the generation of environmentally benign process heat.
“…These benefits are to some extent hampered by the fact that the parent NBD does not absorb light above 267 nm [10] . Therefore, a triplet photosensitizer is necessary to facilitate the light‐induced isomerization of unsubstituted NBD to the energy‐rich QC [8a, 25] . During this work, we opted to utilize acetophenone as a photosensitizer.…”
Cobalt catalysts are immobilized on the surface of iron oxide nanoparticles for the preparation of highly active quasi‐homogeneous catalysts toward an efficient release of photochemically stored energy in norbornadiene‐based photoswitches. The facile separation of the iron oxide nanoparticles through exploitation of the intrinsic magnetic properties of this material enables efficient cyclization of energy storage and release. Through the transition from cobalt (II) salphen to cobalt porphyrins, a 22.6‐fold increase in the catalytic efficiency of the QC‐NBD back‐conversion is achieved, with an initial TOF of up to 3.64 s−1 and excellent TON of over 3305. In addition, a series of novel “push–pull” functionalized norbornadiene derivatives is prepared, featuring excellent absorption properties with maxima up to 366 nm, quantum yields around 70 %, high energy storage capacities of up to 98.0 kJ mol−1, and outstanding thermal stability with t1/2 (25 °C) over 100 days. Finally, the energy storage potential of these molecular solar thermal (MOST) systems is harnessed in a heat release experiment. This demonstrates the potential of norbornadiene‐based photoswitches in combination with efficient magnetic catalysts for the generation of environmentally benign process heat.
“…According to the literature, acetophenone is ideal for this purpose. [5] Irradiation of am ixture of malonate 2 and 5mol %a cetophenone in diethyl ether resulted in the formation of the desired QC malonate. To our surprise the successive Bingel-Hirsch reaction with this malonate did not give the expected product.…”
Section: Resultsmentioning
confidence: 99%
“…[4] Hence, at riplet photosensitizer with E T (sensitizer) > E T (NBD),s uch as acetophenone or benzophenone, is neededt oe nable the isomerization of neat NBD to QC. [5] Alternatively,i th as been shown that, by functionalization of the NBD scaffold, it is possible to redshift the absorption and simultaneously increase the quantum yield. [6] However,f unctionalization of the NBD scaffoldnaturally is alwaysa ccompanied with an increased molecular weight and, therefore, al ower energy storage density.N ext to the photoisomerization, also the corresponding back reactionf rom QC to NBD mustb ec onsidered and optimized.…”
The synthesis and propertieso fv arious norbornadiene/quadricyclane (NBD/QC)f ullerene hybrids are reported. By cyclopropanation of C 60 with malonates carrying the NBD scaffold as mall library of NBD-fullerenem onoadducts and NBD-fullereneh exakisadducts was established. The substitutionp attern of the NBD scaffold, as well as the electron affinity of the fullerenec ore within these hybrid systems,has ap ronouncedi mpact on the properties of the corresponding energy rich QC derivatives. Based on this, the first direct photoisomerization of NBD-fullerene hybridst ot heir QC derivatives was achieved.F urthermore, it was possible to use the redox-active fullerenec ore of aQ C-fullerene monoadduct to enable the back reactiont of orm the corresponding NBD-fullerenem onoadduct. Combining theset wo processes enabless witching between NBD and QC simply by changing the irradiationw avelength between3 10 and 400 nm. Therefore, turning this usually photo/thermal switch into ap ure photoswitch. This not only simplifies the investigationo ft he underlying processes of the NBD-QC interconversion within the system,b ut also renders such hybrids interesting for applications as molecular switches.
“…In addition to direct chemical modification, different photophysical methods have also been explored, including the use of sensitizers [48][49][50][51] and more recently, the use of photon upconversion systems. The latter systems convert low-energy photons that otherwise cannot be absorbed by the molecules into higher-energy photons.…”
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