Promoting the Furan Ring-Opening Reaction to Access New Donor-Acceptor Stenhouse Adducts with Hexafluoroisoproponal

Donor–acceptor Stenhouse adducts (DASAs) are visible‐light‐responsive photoswitches with a variety of emerging applications in photoresponsive materials. Their two‐step modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) promotes the ring‐opening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASA‐based photoswitches and DASA–polymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1H NMR and UV/Vis spectroscopy. The use of sterically hindered, electron‐poor amines enabled the dark equilibrium to be decoupled from closed‐isomer half‐lives for the first time

Visible light-responsive materials: the (photo)chemistry and applications of donor–acceptor Stenhouse adducts in polymer science

Donor-acceptor Stenhouse adduct (DASA) photoswitches have gained a lot of attention since their discovery in 2014. Their negative photochromism, visible light absorbance, synthetic tunability, and the large property changes between their photoisomers make them attractive candidates over other commonly used photoswitches for use in materials with responsive or adaptive properties. The development of such materials and their translation into advanced technologies continues to widely impact forefront materials research, and DASAs have thus attracted considerable interest in the field of visible-light responsive molecular switches and dynamic materials. Despite this interest, there have been challenges in understanding their complex behavior in the context of both small molecule studies and materials. Moreover, incorporation of DASAs into polymers can be challenging due to their incompatibility with the conditions for most common polymerization techniques. In this review, therefore, we examine and critically discuss the recent developments and challenges in the field of DASA-containing polymers, aiming at providing a better understanding of the interplay between the properties of both constituents (matrix and photoswitch). The first part summarizes current understanding of DASA design and switching properties. The second section discusses strategies of incorporation of DASAs into polymers, properties of DASA-containing materials, and methods for studying switching of DASAs in materials. We also discuss emerging applications for DASA photoswitches in polymeric materials, ranging from light-responsive drug delivery systems, to photothermal actuators, sensors and photoswitchable surfaces. Last, we summarize the current challenges in the field and venture on the steps required to explore novel systems and expand both the functional properties and the application opportunities of DASA-containing polymers

Donor‐acceptor Stenhouse adduct-polydimethylsiloxane-conjugates for enhanced photoswitching in bulk polymers

Donor–acceptor Stenhouse adducts (DASAs) are a rapidly emerging class of visible light-activated photochromes and DASA-functionalized polymers hold great promise as biocompatible photoresponsive materials. However, the photoswitching performance of DASAs in solid polymer matrices is often low, particularly in materials below their glass transition temperature. To overcome this limitation, DASAs are conjugated to polydimethylsiloxanes which have a glass transition temperature far below room temperature and which can create a mobile molecular environment around the DASAs for achieving more solution-like photoswitching kinetics in bulk polymers. The dispersion of DASAs conjugated to such flexible oligomers into solid polymer matrices allows for more effective and tunable DASA photoswitching in stiff polymers, such as poly(methyl methacrylate), without requiring modifications of the matrix. The photoswitching of conjugates with varying polymer molecular weight, linker type, and architecture is characterized via time-dependent UV–vis spectroscopy in organic solvents and blended into polymethacrylate films. In addition, DASA-functionalized polydimethylsiloxane networks, accessible via the same synthetic route, provide an alternative solution for achieving fast and efficient DASA photoswitching in the bulk owing to their intrinsic softness and flexibility. These findings may contribute to the development of DASA-functionalized materials with better tunable, more effective, and more reversible modulation of their optical properties

Promoting the furan ring opening reaction to access new donor–acceptor stenhouse adducts with hexafluoroisopropanol

Donor–acceptor Stenhouse adducts (DASAs) are visible-light-responsive photoswitches with a variety of emerging applications in photoresponsive materials. Their two-step modular synthesis, centered on the nucleophilic ring opening of an activated furan, makes DASAs readily accessible. However, the use of less reactive donors or acceptors renders the process slow and low yielding, which has limited their development. We demonstrate here that 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) promotes the ring-opening reaction and stabilizes the open isomer, allowing greatly reduced reaction times and increased yields for known derivatives. In addition, it provides access to previously unattainable DASA-based photoswitches and DASA–polymer conjugates. The role of HFIP and the photochromic properties of a set of new DASAs is probed using a combination of 1H NMR and UV/Vis spectroscopy. The use of sterically hindered, electron-poor amines enabled the dark equilibrium to be decoupled from closed-isomer half-lives for the first time

Visible light-responsive materials : the (photo)chemistry and applications of donor–acceptor Stenhouse adducts in polymer science

Donor–acceptor Stenhouse adduct (DASA) photoswitches have gained a lot of attention since their discovery in 2014. Their negative photochromism, visible light absorbance, synthetic tunability, and the large property changes between their photoisomers make them attractive candidates over other commonly used photoswitches for use in materials with responsive or adaptive properties. The development of such materials and their translation into advanced technologies continues to widely impact forefront materials research, and DASAs have thus attracted considerable interest in the field of visible-light responsive molecular switches and dynamic materials. Despite this interest, there have been challenges in understanding their complex behavior in the context of both small molecule studies and materials. Moreover, incorporation of DASAs into polymers can be challenging due to their incompatibility with the conditions for most common polymerization techniques. In this review, therefore, we examine and critically discuss the recent developments and challenges in the field of DASA-containing polymers, aiming at providing a better understanding of the interplay between the properties of both constituents (matrix and photoswitch). The first part summarizes current understanding of DASA design and switching properties. The second section discusses strategies of incorporation of DASAs into polymers, properties of DASA-containing materials, and methods for studying switching of DASAs in materials. We also discuss emerging applications for DASA photoswitches in polymeric materials, ranging from light-responsive drug delivery systems, to photothermal actuators, sensors and photoswitchable surfaces. Last, we summarize the current challenges in the field and venture on the steps required to explore novel systems and expand both the functional properties and the application opportunities of DASA-containing polymers

Urbanism and architecture facing major risks and sustainable development: the urban zone of Pointe-à-Pitre in Guadeloupe

The urban zone of Pointe-à-Pitre in Guadeloupe, located in the middle of a concentration of 132 000 inhabitants, has many functions : political, administrative and commercial. Its tourist importance is essential for Guadeloupe. At last but not least, the place of Pointe-à-Pitre in the collective unconscious is predominant, it has so a first level social function. Today, the urban morphology and typology of the town is not able to face a seismic disaster. Its vulnerability to the others major risks is less important. I made a deep historic study that, with the help of plans, maps and texts, allowed me to recount the urban morphology and typology history of the urban zone, through the main major risks that have affected and can affect still now that centre : earthquakes, cyclones and fires. I analyse too, facing major risks, the public highways and all the infrastructures of the territory. The existing references on the seismic activity to the Antilles relate only to approximately 3 centuries. Thus, many uncertainties remain on the seismic risk to which Guadeloupe is subjected. One proposes here to analyze these various uncertainties in order to permit a finer approach of the seismic risk for that territory. The studied elements permit to understand better the vulnerability of that centre to the major risks.Pointe-à-Pitre est située au centre d’une agglomération urbaine de 132 000 habitants dont elle draine chaque jour les habitants. Cette ville a de nombreuses fonctions, qu’elles soient politiques, administratives, touristiques ou commerciales. Sa place dans l’inconscient collectif est prépondérante et elle a ainsi un rôle social de première importance. Aujourd’hui, l’agglomération pointoise ne peut faire face dans de bonnes conditions à un séisme majeur. Sa vulnérabilité aux autres risques est moins importante. Les références existantes sur l’activité sismique aux Antilles ne portent que sur environ 3 siècles ; de nombreuses incertitudes subsistent sur l’aléa sismique auquel est soumise la Guadeloupe, et les séismes historiques sont actuellement estimés avec des marges d’erreur certaines. On se propose ici d’analyser ces différentes incertitudes pour permettre une approche plus fine de l’exposition au risque de la Guadeloupe. Nous avons réalisé une étude historique très poussée qui, à l’aide de plans, de cartes et de textes, nous a permis de reconstituer l’histoire de la morphologie urbaine et de la typologie architecturale de l’agglomération pointoise, à travers les risques majeurs principaux auxquels elle est exposée : les séismes, les cyclones et les incendies. Nous avons aussi analysé, sur le territoire de l’agglomération, les voiries et réseaux divers au regard des risques majeurs. Les éléments étudiés nous permettent de mieux comprendre la vulnérabilité de cette agglomération dans son ensemble