Preparation and Kinetic Stabilization of Highly Strained Paracyclophanes

Tsuji, Takashi; Ohkita, Masakazu; Kawai, Hidetoshi

doi:10.1246/bcsj.75.415

Cited by 15 publications

(5 citation statements)

References 93 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…No substitution pattern is known that significantly increases the activation barrier for Z / E isomerization above that of unsubstituted azobenzene. 105 The mechanisms of E/Z photo-and thermal isomerization remain controversial. Isomerization may occur by rotation about the N]N bond, by inversion of one of the N atoms or a combination of the two (concerted inversion, 106-108 Fig.…”

Section: Photoisomerization Of Double Bondsmentioning

confidence: 99%

Chemical solutions for the closed-cycle storage of solar energy

Kucharski

Tian

Akbulatov

et al. 2011

Energy Environ. Sci.

262

253

View full text Add to dashboard Cite

This review analyzes the inherent scientific challenges of realizing the potential of storing solar energy by photochemical generation of high-energy metastable compounds whose subsequent thermal isomerization releases large amounts of low-temperature (<500 K) heat. Such compounds may be stored at room temperature for days or months, regenerated using sunlight, and may be cycled many times without significant degradation. After highlighting some of the general challenges of solar energy conversion and storage, we discuss how recent advances in understanding the effect of molecular strain on the thermal and photochemical reactivity of small molecules offers new opportunities for a systematic approach to the molecular design of solar thermal fuels, defining the molecular properties which determine the fundamental limits of such a material's performance characteristics.

show abstract

Section: Photoisomerization Of Double Bondsmentioning

confidence: 99%

Chemical solutions for the closed-cycle storage of solar energy

Kucharski

Tian

Akbulatov

et al. 2011

Energy Environ. Sci.

262

253

View full text Add to dashboard Cite

show abstract

“…As an energy storage medium , this leads to a rather poor energy density, and, more importantly, the activation energy barrier of the cis→trans back reaction is low (<1 eV), corresponding to a half life of only a few hours for the metastable state . No substitution pattern is known that significantly increases the activation barrier or the stored energy above that of unsubstituted AB, making it unpractical in its isolated state for solar thermal fuel applications.…”

mentioning

confidence: 99%

Photoswitchable Molecular Rings for Solar-Thermal Energy Storage

Durgun

Grossman

2013

J. Phys. Chem. Lett.

View full text Add to dashboard Cite

Solar-thermal fuels reversibly store solar energy in the chemical bonds of molecules by photoconversion, and can release this stored energy in the form of heat upon activation. Many conventional photoswichable molecules could be considered as solar thermal fuels, although they suffer from low energy density or short lifetime in the photoinduced high-energy metastable state, rendering their practical use unfeasible. We present a new approach to the design of chemistries for solar thermal fuel applications, wherein well-known photoswitchable molecules are connected by different linker agents to form molecular rings. This approach allows for a significant increase in both the amount of stored energy per molecule and the stability of the fuels. Our results suggest a range of possibilities for tuning the energy density and thermal stability as a function of the type of the photoswitchable molecule, the ring size, or the type of linkers. SECTION:Energy Conversion and Storage; Energy and Charge Transport E fficient utilization of the sun as a renewable and clean energy source is one of the greatest goals and challenges of this century due to the increasing demand for energy and its environmental impact. Numerous strategies exist to convert sunlight into useful forms of energy, including photocatalytic processes, artificial photosynthesis, 1,2 photothermal power plants, 3 and photovoltaic applications. 4 An alternative strategy to these is to convert and store the sun's energy directly in the chemical bonds of metastable photoisomers of suitable molecular systems. The stored energy can then be released as heat on demand by an external trigger. Ideally both the photisomerization and heat release reactions reversibly occur in a closed-cycle without changing the chemical composition. 5The clear advantage of such an approach is that the same material both converts and stores the sun's energy, providing a rechargeable fuel that can be safely transported and used ondemand; the materials used could, in principle, be cheap, nontoxic and abundant, and the cycle can be repeated thousands of times without any emission or waste.The idea of storing solar energy in chemical bonds was first introduced with the photoisomerization reactions of organic molecules (such as norbornadiene⇌quadricyclane 6,7 and the trans⇌cis isomers of azobenzene 8 ), although the concept was generally dismissed as unpractical 7 due to a number of reasons including degradation, instability of the photoinduced isomer (limited half-life or shelf life), low energy density, and cost. As such, the majority of recent experimental studies for such materials have focused on their photoswitchable properties, 9 as opposed to energy storage. The Ru-based organometallic complex (tetracarbonyl−diruthenium fulvalene) 10 has shown promise as a solar thermal fuel due to its high cyclability without degradation; however, substitutions for Ru must be found to reduce costs, and the volumetric energy density increased for practical applications. 11,12 Recently, a new s...

show abstract

“…While the main interest in the latter group arises from a supramolecular point of view originating from their ability of being interesting vehicles for hostguest chemistry, 5,6,8,25,29 the 'small' phanes, with [n]cyclophanes as the archetype of this group, constitute a model for studies on fundamental aspects of strain and aromaticity. 11,[71][72][73][74][75][76][77][78][79][80] The short bridges in such cyclophanes often prohibit free rotation of the rings and thus place these molecular portions into unusual and thermodynamically often disfavored orientations to each other, which would never be observed in open-chain systems. The cyclic core can even impart such strain on the whole system that the benzene ring is twisted out of plane and adopts a boat-or chairlike configuration, depending on the type of cyclophane.…”

Section: Strain In Cyclophane Natural Productsmentioning

confidence: 99%

“…Even ring closure via peptide-bond formation, which could not been realized for the 14-membered systems, was possible, e.g. in the synthesis of OF4949-III (80). Schmidt accomplished the construction of the peptide ring in natural product 80 in a two-step conversion (Scheme 13, top).…”

Section: Isodityrosine-containing Peptidesmentioning

confidence: 99%

Strained cyclophane natural products: Macrocyclization at its limits

2012

View full text Add to dashboard Cite

Cyclophane natural products comprise an intriguing class of structurally diverse compounds. As inherent for all cyclic compounds regardless of their origin, macrocyclization is naturally the most decisive step, which defines the overall efficiency of the synthetic pathway. Especially in small cyclophane molecules, this key step constitutes an even greater challenge. Due to the strain imparted by the macrocyclic system, free rotation of the benzene ring(s) is often restricted depending on both the constitution of the tether and the aromatic portions. Not surprisingly, the synthesis of natural cyclophanes with their often outstanding pharmaceutical activities and the inherent issues associated with their preparation has attracted much attention among the synthetic community. In particular, it stimulated the development of new strategies for the ring-closing step, as often otherwise well established and robust reactions fail to perform effectively. In this review, we describe the challenges synthetic chemists are facing during the synthesis of this small, but structurally and biologically fascinating class of natural products, concentrating on the representatives exhibiting configurational stability. The main focus will be on the different concepts for the installation of the macrocyclic system, in most cases the central problem in assembling these extremely rigid molecules.

show abstract

Preparation and Kinetic Stabilization of Highly Strained Paracyclophanes

Cited by 15 publications

References 93 publications

Chemical solutions for the closed-cycle storage of solar energy

Chemical solutions for the closed-cycle storage of solar energy

Photoswitchable Molecular Rings for Solar-Thermal Energy Storage

Strained cyclophane natural products: Macrocyclization at its limits

Contact Info

Product

Resources

About