Photochemical Reactions in Supramolecular Assemblies of Gels: Dimerizations and Polymerizations via Pericyclic Reactions

Abstract

Gel state reactions offer new direction for the reactivity of the organic molecules or metal‐organic materials upon photoirradiation with shorter reaction times and high yields compared to solid and solution states. The restricted molecular movement among the molecules in the soft solids control the stereoselectivity of the photoproducts in the gel state reactions. To date, most of the strategies based on self‐assembly have been demonstrated in the solid state, in particular for [2+2] reactions of olefins and polymerization reactions of diacetylenes via 1,4 addition. The soft materials are of emerging materials in recent days given their many applicative day‐to‐day aspects. This review gives a glimpse of recent reports on pericyclic reactions in the gel state that are designed based on the self‐assembly concept. Also it highlights how such reactions accompany the physical changes in the structure of the gels and stereo controlled products with high yields.

Organic Polymers of an Angular Diene via Solid State [2 + 2] Polymerization: Coordination Polymers with Dicarboxylates as Templates

“…The design and synthesis of novel organic polymers through topochemical reactions, such as [2 + 2], [4 + 4], [4 + 2], and [1,4]-addition are of recent interest owing to ease of synthesis with deducible and tunable structural features in high yields and also due to the day-to-day applicative aspects of the organic polymers. − In particular, the synthesis of crystalline 1D and 2D organic polymers containing cyclobutanes in the backbone through [2 + 2] reactions of diene and trienes, respectively, are of immense interest given their uniqueness and difficulty in finding such monomers with requisite crystal structures. − Integrating such monomers of dienes into the network of coordination polymers was shown to promote [2 + 2] polymerization reactions to produce coordination polymers of organic polymers (CPOPs) in single crystal to single crystal transformations upon irradiation. − …”

Stimuli responsive dynamic transformations in supramolecular gels

“…A common pattern of reactivity of the chromophores can be identified which includes trans-cis photoisomerization, photodimerization and photopolymerization, electrocyclic reactions, photoredox reaction etc. [101][102][103][104] Such photochemical reactions often either lead to gelation or trigger gel-to-sol phase transformations. However, few structurally designed LMWGs are found that execute changes in material properties like viscosity, rigidity, morphology transformations, swelling, or electronic properties in response to light without phase transformations.…”

Photo-responsive metal–organic gels of rigid phenylene-1,3-di-substituted angular dienes with metal halides: gel-to-gel transformations triggered by [2 + 2] polymerization

“…Since the seminal work of Schmidt et al in the 1960s, a template strategy via hydrogen/halogen bonds and/or argentophilic interactions has been proven to be effective for achieving [2 + 2] photo di/polymerization reactions in pure organic solids, coordination polymers (CPs), and metal-organic gels (MOGs). [33][34][35][36][37][38][39][40][41][42] In crystalline solids, the reactions occur in a confined environment where the movement of molecules is arrested and double bonds are arranged in parallel with a distance of 3.5 to 4.2 Å. Unlike crystalline solids, gels can provide the stimuli-responsive movements of molecules to attain the reactive geometries.…”