Substituted Diarylnorbornadienes and Quadricyclanes: Synthesis, Photochemical Properties, and Effect of Substituent on the Kinetic Stability of Quadricyclanes

Spivack, Kyle J.; Walker, Jesse V.; Sanford, Maria J.; Rupert, Benjamin R.; Ehle, Andrew R.; Tocyloski, James M.; Jahn, Aaron N.; Shaak, Lyndsey M.; Obianyo, Obiamaka; Usher, Karyn M.; Goodson, Felix E.

doi:10.1021/acs.joc.6b02025

Cited by 16 publications

(8 citation statements)

References 45 publications

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“…Photoswitches that can absorb and store solar energy and release it as heat on demand have been considered as candidates for MOST applications. These systems have attracted increasing attention in the last years due to their possible use in emission-free energy storage systems. − …”

Section: Introductionmentioning

confidence: 99%

Engineering of Norbornadiene/Quadricyclane Photoswitches for Molecular Solar Thermal Energy Storage Applications

2020

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Conspectus Renewable energy resources are mostly intermittent and not evenly distributed geographically; for this reason, the development of new technologies for energy storage is in high demand. Molecules that undergo photoinduced isomerization reactions that are capable of absorbing light, storing it as chemical energy, and releasing it as thermal energy on demand are referred to as molecular solar thermal energy storage (MOST) or solar thermal fuels (STF). Such molecules offer a promising solution for solar energy storage applications. Different molecular systems have been investigated for MOST applications, such as norbornadienes, azobenzenes, stilbenes, ruthenium derivatives, anthracenes, and dihydroazulenes. The polycyclic strained molecule norbornadiene (NBD), which photoconverts to quadricyclane (QC), is of great interest because it has a high energy storage density and the potential to store energy for a very long time. Unsubstituted norbornadiene has some limitations in this regard, such as poor solar spectrum match and low quantum yield. In the past decade, our group has developed and tested new NBD systems with improved characteristics. Moreover, we have demonstrated their function in laboratory-scale test devices for solar energy harnessing, storage, and release. This Account describes the most impactful recent findings on how to engineer key properties of the NBD/QC system (photochemistry, energy storage, heat release, stability, and synthesis) as well as examples of test devices for solar energy capture and heat release. While it was known that introducing donor–acceptor groups allows for a red-shifted absorption that better matches the solar spectrum, we managed to introduce donor and acceptor groups with very low molecular weight, which allowed for an unprecedented solar spectrum match combined with high energy density. Strategic steric hindrance in some of these systems dramatically increases the storage time of the photoisomer QC, and dimeric systems have independent energies barriers that lead to an improved solar spectrum match, prolonged storage times, and higher energy densities. These discoveries offer a toolbox of possible chemical modifications that can be used to tune the properties of NBD/QC systems and make them suitable for the desired applications, which can be useful for anyone wanting to take on the challenge of designing efficient MOST systems. Several test devices have been built, for example, a hybrid MOST device that stores sunlight energy and heat water at the same time. Moreover, we developed a device for monitoring catalyzed QC to NBD conversion resulting in the possibility to quantify a significant macroscopic heat generation. Finally, we tested different formulations of polymeric composites that can absorb light during the day and release the energy as heat during the night for possible use in future window coating applications. These lab-scale realizations are formative and contribute to pushing the field forward towar...

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Section: Introductionmentioning

confidence: 99%

Engineering of Norbornadiene/Quadricyclane Photoswitches for Molecular Solar Thermal Energy Storage Applications

2020

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“…12−14 Accordingly, the effect of various substitution patterns on absorption profile, photoisomerization, storage density, and kinetic stability of the QC isomer has been studied rather extensively. 6,8,15,16 Since, to date, most NBD-QC systems require solvation, with very few exceptions, 17 both absorption spectrum and quantum yield can be tuned by the choice of solvent. Yet, while solvent conditions are known to have an effect on the switching for other potential MOST candidates, such as azobenzene, 18−22 stilbene, 23−25 tetracarbonyl−fulvalene−diruthenium 26 and dihydroazulene, 27,28 to the best of our knowledge, the impact of solvation has not been systematically studied for NBD-QC systems.…”

Section: ■ Introductionmentioning

confidence: 99%

Solvent Effects on the Absorption Profile, Kinetic Stability, and Photoisomerization Process of the Norbornadiene–Quadricyclanes System

et al. 2019

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Molecular photoswitches based on the norbornadiene−quadricyclane (NBD-QC) couple can be used to store solar energy and to release the stored energy as heat on demand. In this context, the energy storage time as well as the quantum yield of the energy storing reaction are important parameters. Here, we explore for the first time solvent effects on these processes for a series of four NBD-QC compounds in four different solvents with different polarity (acetonitrile, tetrahydrofuran, toluene, and hexane). We show that the energy storage time of the QC forms can vary by up to a factor of 2 when going from the most to the least polar solvent. Moreover, we show that for the norbornadiene derivatives with an asymmetric 1,2 substitution pattern, the quantum yield of conversion is highly solvent dependent, whereas this is not the case for the symmetrically substituted compounds. The spectroscopic observations are further rationalized using classical molecular dynamics (MD) simulations and time-dependent density functional theory (TDDFT) calculations. These demonstrate the importance of vibrational and rotational excitations for obtaining broad-band absorption, which is a prerequisite for capturing a wide range of the solar spectrum.

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“…Therefore, the values of the measured t 1/2 are only indicative in a qualitative way, and fall between 3 and 200 min. Considering that most of the NBD and derivatives are reported to have a radical mechanism for the back reaction that has been reported to be insensitive to solvents, it is surprising that the t 1/2 changes from hours to minutes when passing from solution to neat samples. One possible explanation is that upon conversion of one quadricyclane molecule the heat is released locally and hence likely to trigger the thermally activated conversion in neighboring molecules.…”

Section: Resultsmentioning

confidence: 99%

“…NBD ( 1 in Scheme ) and its derivatives undergo photoisomerization to the highly strained quadricyclane (QC, 2 in Scheme ) upon irradiation with UV or visible light . By molecular design, the system has been optimized toward MOST applications, and the best NBD derivatives fulfil several of the requirements for a functional system, such as high photoisomerization quantum yield, redshifted absorption, high energy storage densities, and very long half‐life of the high energy isomer . However, some key challenges remain, for example, substituents, which are needed to improve the solar spectrum match and thus quantum yield of unsubstituted norbornadiene, typically reduce the energy density .…”

Section: Introductionmentioning

confidence: 99%

Liquid Norbornadiene Photoswitches for Solar Energy Storage

Dreos

Wang

Udmark

et al. 2018

Advanced Energy Materials

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been widely implemented [1] but longterm storage of the heat at higher temperatures remains a challenge, limiting broader applications of solar heating. [2,3] Solar thermal energy can be stored for example as thermal energy in rocks or hot water, in phase change materials, [4,5] or in thermochemical energy storage materials. [6] A particular challenge is to identify compact thermal storage solutions capable of operating in the medium temperature range (100-180 °C). [2] In this context, one possible solution is to use molecular photoswitches where the solar energy is stored in high energy photoisomers. [7] This way of storing solar energy has been referred to as molecular solar thermal (MOST) [8] energy storage or solar thermal fuels. [9] MOST systems are based on a parent molecule, which upon irradiation photoisomerizes to a highenergy isomer. The stored energy can be released on demand by applying heat or by using a catalyst to trigger the thermal back isomerization (Scheme 1). [7,10,11] Various molecular designs have been explored in this context, including ruthenium compounds, [8,12] azobenzene derivatives, [13][14][15][16][17][18] norbornadiene (NBD) derivatives, [10,11,19] dihydroazulenes, [20] and others. [21] The requirements for an efficient MOST system [7,10,22] can be summarized as: (i) good spectral overlap of parent molecule absorptions with the solar spectrum, (ii) minimal absorption of the high energy isomer in the solar spectrum, (iii) high quantum yield for the photoisomerization, (iv) high energy storage density, (v) high kinetic stability of the metastable photoisomer, and (vi) high cyclability. It is also fundamental to obtain neat liquid or solid functional MOST materials (depending on the desired applications), since dilution in solvents or solid matrix lowers the energy storage density. A closed MOST system has been previously described, [23] which involves cycles of an MOST fluid in a solar collector for the photoconversion, a storage tank, and a heat extractor part (see Scheme 1).NBD (1 in Scheme 1) and its derivatives undergo photoisomerization to the highly strained quadricyclane (QC, 2 in Scheme 1) upon irradiation with UV or visible light. [24] By molecular design, the system has been optimized toward MOST applications, and the best NBD derivatives fulfil several of the requirements for a functional system, such as high photoisomerization quantum yield, redshifted absorption, high energy storage densities, and very long half-life of the Due to high global energy demands, there is a great need for development of technologies for exploiting and storing solar energy. Closed cycle systems for storage of solar energy have been suggested, based on absorption of photons in photoresponsive molecules, followed by on-demand release of thermal energy. These materials are called solar thermal fuels (STFs) or molecular solar thermal (MOST) energy storage systems. To achieve high energy densities, ideal MOST systems are required either in solid or liquid forms. In the case of the latter, neat high ...

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Substituted Diarylnorbornadienes and Quadricyclanes: Synthesis, Photochemical Properties, and Effect of Substituent on the Kinetic Stability of Quadricyclanes

Cited by 16 publications

References 45 publications

Engineering of Norbornadiene/Quadricyclane Photoswitches for Molecular Solar Thermal Energy Storage Applications

Engineering of Norbornadiene/Quadricyclane Photoswitches for Molecular Solar Thermal Energy Storage Applications

Solvent Effects on the Absorption Profile, Kinetic Stability, and Photoisomerization Process of the Norbornadiene–Quadricyclanes System

Liquid Norbornadiene Photoswitches for Solar Energy Storage

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