Solid-state Photoreaction Research Articles

Solid-State [2+2] Photoreaction of Isostructural Cd(II) Metal Complexes and Solid-State Fluorescence.

A green method to synthesize cyclobutane derivatives has been developed over the past three decades in the form of solid-state [2+2] photochemical reactions. These solid-state reactions also play a major role in the structural transformation of hybrid materials. In this regard, crystal engineering has played a major role in designing photoreactive molecular systems. Here, we report three novel binuclear Cd(II) complexes with the molecular formula [Cd2(4spy)4L4], where 4spy = 4-styryl pyridine and L = p-toluate (1); 4-fluorobenzoate (2); and 3-fluorobenzoate (3). Although three different benzoates are used, all three complexes are isostructural, as corroborated through SCXRD experiments. Structural analysis also helped in identifying two potential photoreactions. These are both intra- and intermolecular in nature and are driven by the head-to-head (HH) and head-to-tail (HT) alignment of 4spy linkers within these metal complexes. 1H NMR spectroscopy studies showed evidence of a quantitative head-to-head photoreaction in all these three complexes, and SCXRD analysis of the recrystallization of the photoproducts also provided confirmation. TGA studies of these photoreactive complexes showed an increase in the thermal stability of the complexes due to the solid-state photoreaction. Photoluminescence studies of these complexes have been conducted, showing a blue shift in emission spectra across all three cases after the photoreaction.

Using potassium bromide pellets and optical spectroscopy to assess the photodimerization of two trans-(trifluoromethyl)-cinnamic acid compounds

Solid state photoreactions are an attractive route to produce special isomers due to the crystal packing of the starting molecules. We use powder samples pressed into potassium bromide pellets to investigate photoreactions with optical spectroscopy.

3-Pyridylvinyl benzoxazole-derived multifunctional organic materials—from solid-state photoreactivity to photophysical and electrochemical properties

Crystal structure, solid-state photoreactivity and multifunctional materials properties of 3-pyridylvinyl benzoxazole-derived compounds, e.g., photophysical and redox properties, are presented.

Construction of olefinic coordination polymer single crystal platforms: precise organic synthesis, in situ exploration of reaction mechanisms and beyond.

Olefin [2+2] photocycloaddition reactions based on coordination-bond templates provide numerous advantages for the selective synthesis of cyclobutane compounds. This review outlines the recent advances in the design and construction of single crystal platforms of olefinic coordination polymers for precise organic synthesis, in situ exploration of reaction mechanisms, and possible developments as comprehensively as possible. Numerous examples are presented to illustrate how the arrangements of the olefin pairs influence the solid-state photoreactivity and examine the types of cyclobutane products. Furthermore, the photocycloaddition reaction mechanisms are investigated by combining advanced techniques such as single crystal X-ray diffraction, powder X-ray diffraction, nuclear magnetic resonance, infrared spectroscopy, fluorescence spectroscopy, laser scanning confocal microscopy and theoretical calculations. Finally, potential applications resulting from promising physicochemical properties before and after photoreactions are discussed, and existing challenges and possible solutions are also proposed.

Unraveling the Solid-State Photoreactivity of Carbonylbis(4,1-Phenylene)dicarbonazidate with Laser Flash Photolysis.

Solid-state photoreactions are generally controlled by the rigid and ordered nature of crystals. Herein, the solution and solid-state photoreactivities of carbonylbis(4,1-phenylene)dicarbonazidate (1) were investigated to elucidate the solid-state reaction mechanism. Irradiation of 1 in methanol yielded primarily the corresponding amine, whereas irradiation in the solid state gave a mixture of photoproducts. Laser flash photolysis in methanol showed the formation of the triplet ketone (TK) of 1 (τ ∼ 99 ns), which decayed to triplet nitrene 31N (τ ∼ 464 ns), as assigned by comparison to its calculated spectrum. Laser flash photolysis of a nanocrystalline suspension and diffuse reflectance laser flash photolysis also revealed the formation of TK of 1 (τ ∼ 106 ns) and 31N (τ ∼ 806 ns). Electron spin resonance spectroscopy and phosphorescence measurements further verified the formation of 31N and the TK of 1, respectively. In methanol, 31N decays by H atom abstraction. However, in the solid state, 31N is sufficiently long lived to thermally populate its singlet configuration (11N). Insertion of 11N into the phenyl ring to produce oxazolone competes with 31N cleavage to form a radical pair. Notably, 1 did not exhibit photodynamic behavior, likely because the photoreaction occurs only on the crystal surfaces.

Regulation of Crystal Structures and Solid-State Photoreactivity of Diolefin Coordination Polymers by Carboxylate Ligands.

Olefinic coordination polymers (CPs) have recently drawn more attention, owing to the many possibilities in conformational conversions and photochemical reactivity that olefin molecules offer. In the presence of different carboxylic acids, we utilize one diolefin ligand 4,4'-((1E,1'E)-(2,5-dimethoxyl-1,4-phenylene)bis(ethene-2,1-diyl))dipyridine (OCH3-bpeb) and Cd(II) to assemble six different crystalline CPs (1-6). By fine-tuning the substituent size, carboxyl group number, and geometrical configuration of carboxylate ligands, these diolefin CPs show quite different crystal architecture models, from one-dimensional intersecting stacking to one-dimensional parallel stacking to three-dimensional interpenetrated structure. Of these, four kinds of CPs (1, 2, 5, and 6) are demonstrated to be photoreactive for [2 + 2] cycloaddition reactions, as confirmed by proton nuclear magnetic resonance and single-crystal X-ray diffraction. Both 2 and 5 can be dimerized into different cyclobutane products in a single-crystal-to-single-crystal manner under visible light, and remarkably, the photocycloaddition reaction of 5 involves a rare phase transition with structural symmetry enhancement from P1̅ to P2/n. This work demonstrates the power of carboxylate ligands in tuning single crystal structures and photocycloaddition reactions of CPs, which provides important references for the further exploration of other physicochemical properties of functionalized olefin-containing complexes.

Silver(i) coordination polymers of trans-5-styrylpyrimidine – from structural diversity to solid-state reactivity under sunlight

Structural diversity and sunlight driven solid state photo-reactivity of a series of one-dimensional silver(i) coordination polymers of trans-5-styrylpyrimidine are demonstrated.

Engineering solid-state photoreactivity within silver(I) organosulfonate complexes containing an ester-functionalized reactant molecule

The formation, structure, and photoreactivity of a pair of silver(I) complexes based upon either trifluoromethanesulfonate [Ag(CF3SO3)] or p-toluenesulfonate [Ag(C7H7SO3)] anions along with the ester-based reactant molecule trans-1-(4-methylbenzoate)-2-(4-pyridyl)ethylene (1) are reported. In both complexes, silver(I) ions form coordinated covalent bonds to the 4-pyridyl group on the olefin containing reactant molecule and due to either argentophilic interactions or close packing of a pair of silver(I) ions ultimately places a pair of carbon-carbon bonds (C = C) on neighboring molecules of 1 in a suitable position to undergo a solid-state [2 + 2] cycloaddition reaction. In particular, the complexes [Ag(CF3SO3)(1)2]·CH3CN and [Ag2(C7H7SO3)2(1)4] both undergo a quantitative photoreaction to yield the head-to-head photoproduct rctt-1,2-bis(4-methylbenzoate)-3,4-bis(4-pyridyl)cyclobutane (2) upon exposure to ultraviolet light.

A Green Chemistry Approach toward the Stereospecific Synthesis of Densely Functionalized Cyclopropanes via the Solid-State Photodenitrogenation of Crystalline 1-Pyrazolines.

The cyclopropane ring features prominently in active pharmaceuticals, and this has spurred the development of synthetic methodologies that effectively incorporate this highly strained motif into such molecules. As such, elegant solutions to prepare densely functionalized cyclopropanes, particularly ones embedded within the core of complex structures, have become increasingly sought-after. Here we report the stereospecific synthesis of a set of cyclopropanes with vicinal quaternary stereocenters via the solvent-free solid-state photodenitrogenation of crystalline 1-pyrazolines. Density functional theory calculations at the M062X/6-31+G(d,p) level of theory were used to determine the origin of regioselectivity for the synthesis of the 1-pyrazolines; favorable in-phase frontier molecular orbital interactions are responsible for the observation of a single pyrazoline regioisomer. It was also shown that the loss of N2 may take place via a highly selective solid-state thermal reaction. Scalability of the solid-state photoreaction is enabled through aqueous nanocrystalline suspensions, making this method a "greener" alternative to effectively facilitate the construction of cyclopropane-containing molecular scaffolds.

Solid-state photoreactivity of cinnamic acid and crotonic acid compared

Solid-state photoreactivity of cinnamic acid and crotonic acid compared

Collective behavior in the kinetics and equilibrium of solid-state photoreaction

There is current interest in developing photoactive materials that deform on illumination. The strategy is to develop new photoactive molecules in solution, and then to incorporate these in the solid-state either by crystallization or by inserting them into polymers. This letter shows that the kinetics and the nature of the photo-induced phase transitions are profoundly different in single molecules (solution) and in the solid state using a lattice spin model. In solution, where the molecules act independently, the photoreaction follows first-order kinetics. However, in the solid state where the photoactive molecules interact with each other and therefore behave collectively during reaction, photoreactions follow the sigmoidal kinetics of nucleation and growth as in a first-order phase transition. Further, we find that the exact nature of the photo-induced strain has a critical effect on the kinetics, equilibrium, and microstructure formation. These predictions agree qualitatively with experimental observations, and provide insights for the development of new photoactive materials.

Turning On Solid-State Luminescence by Phototriggered Subtle Molecular Conformation Variations.

The development of solid-state intelligent materials, in particular those showing photoresponsive luminescence (PRL), is highly desirable for their cutting-edge applications in sensors, displays, data-storage, and anti-counterfeiting, but is challenging. Few PRL materials are constructed by tethering the classic photochromic systems with newly-emerged solid-state emitters. Selective solid-state photoreactions are demanded to precisely manipulate the luminescent behavior of these emitters, which require dramatic structural change and enough free space, thus limiting the scope of the PRL family. Here, a new PRL material, TPE-4N, that features sensitive and reversible fluorescence switching is reported. The interesting on-off luminescent property of TPE-4N can be facilely tuned through fast phototriggering and thermal annealing. Experimental and theoretical investigations reveal that subtle molecular conformation variation induces the corresponding PRL behavior. The crystalline and amorphous state endows an efficient and weak ISC process, respectively, to turn on and off the emission. The readily fabricated thin-film of TPE-4N exhibits non-destructive PRL behavior with high contrast (>102 ), good light transmittance (>72.3%), and great durability and reversibility under room light for months. Remarkably, a uniform thin-film with such fascinating PRL properties allows high-tech applications in invisible anti-counterfeiting and dynamic optical data storage with micro-resolution.

A diamondoid net sustained by halogen bonds: employing a cyclobutane to generate a tetrahedral architecture

A purely organic dia net sustained by halogen bonds that contains nodes comprised of rctt-tetrakis (4-pyridyl) cyclobutane, obtained from a solid-state photoreaction, is reported.

Astrochemistry and Astrobiology: Materials Sciencein Wonderland?

Astrochemistry and astrobiology, the fascinating disciplines that strive to unravel the origin of life, have opened unprecedented and unpredicted vistas into exotic compounds as well as extreme or complex reaction conditions of potential relevance for a broad variety of applications. Representative, and so far little explored sources of inspiration include complex organic systems, such as polycyclic aromatic hydrocarbons (PAHs) and their derivatives; hydrogen cyanide (HCN) and formamide (HCONH2) oligomers and polymers, like aminomalononitrile (AMN)-derived species; and exotic processes, such as solid-state photoreactions on mineral surfaces, phosphorylation by minerals, cold ice irradiation and proton bombardment, and thermal transformations in fumaroles. In addition, meteorites and minerals like forsterite, which dominate dust chemistry in the interstellar medium, may open new avenues for the discovery of innovative catalytic processes and unconventional methodologies. The aim of this review was to offer concise and inspiring, rather than comprehensive, examples of astrochemistry-related materials and systems that may be of relevance in areas such as surface functionalization, nanostructures, and hybrid material design, and for innovative technological solutions. The potential of computational methods to predict new properties from spectroscopic data and to assess plausible reaction pathways on both kinetic and thermodynamic grounds has also been highlighted.

Varying the regiochemistry from a solid-state [2+2] cycloaddition reaction within a series of mixed co-crystals based upon isosteric resorcinols

A series of regioselective [2 + 2] cycloaddition reactions have been achieved in different mixed co-crystals based upon (E)-methyl-3-(pyridin-3-yl)prop-2-enoate (3-PAMe) as the reactant molecule. The solid-state photoreaction occurred by utilizing a combination of three isosteric resorcinols, namely 4,6-dichlororesorcinol (4,6-diCl res), 4,6-dibromoresorcinol (4,6-diBr res), and 4,6-diiodoresorcinol (4,6-diI res) as hydrogen-bonding templates to align a pair of carbon-carbon double bonds in the correct orientation to photoreact. In each mixed co-crystal, the components form a discrete three-component hydrogen-bonded assembly when upon exposure to UV light produce either the head-to-head (rctt)-dimethyl-3,4-bis(pyridin-3-yl)cyclobutane-1,2-dicarboxylate or the head-to-tail (rctt)-dimethyl-2,4-bis(pyridin-3-yl)cyclobutane-1,3-dicarboxylate photoproducts. In particular, the mixed co-crystal (4,6-diCl/Br res)∙2(3-PAMe) yielded exclusively the head-to-head isomer while both (4,6-diBr/I res)∙2(3-PAMe) and (4,6-diCl/I res)∙2(3-PAMe) produced the head-to-tail isomer.

Size Matters: [2 + 2] Photoreactivity In Macro- and Microcrystalline Salts of 4-Aminocinnamic Acid

The solid-state photoreactivity of 4-aminocinnamic acid (1) and molecular salts [1H]ClO4 and [1H]HSO4 has been investigated, and structural changes have been monitored by X-ray diffraction techniques and FTIR spectroscopy. While the parent compound 1 and its perchlorate salt [1H]ClO4 are photoinert, irradiation of [1H]HSO4 single crystals results in partial single-crystal to single-crystal (SCSC) [2 + 2] photodimerization, with formation of a {[1H]HSO4}0.36·{[12H2][HSO4]2}0.64 solid solution. If crystalline powders of [1H]HSO4 are irradiated, however, the formation of a monomer/dimer solid solution is followed by “extrusion” and recrystallization of both the phodimerization product [12H2]HSO4 and unreacted [1H]HSO4 as nonisomorphous crystal phases. The outcome of the UV irradiation of [1H]HSO4, therefore, is influenced by the crystal size of the reacting monomer and changes dramatically if the irradiated sample is in the form of single macrocrystals or microcrystalline powder.

Flexible oligomer spacers as the key to solid-state photopolymerization of hydrogel precursors

Efficient crosslinking of conventional photoreactive hydrogel precursors relies on the mobility of the reactive groups and is typically addressed from the liquid state. However, this represents a major limitation for many processing techniques of hydrogel materials. Herein, a model precursor is introduced that overcomes this challenge using a prepolymer designed to enable successful crosslinking in the solid state. The precursor is synthesized by connecting a flexible, mono-acrylated spacer to a semi-crystalline hydrophilic backbone polymer using a di-isocyanate linker. The resulting prepolymers exhibit excellent solid-state photoreactivity, even in the absence of a photo-initiator. As a proof of concept, the precursor has successfully been processed by: (1) solution electrospinning with subsequent solid-state photopolymerization (SSPP), (2) melt-based additive manufacturing with subsequent SSPP and (3) two-photon polymerization in the solid state. No cell adhesion takes place on bare crosslinked 3D-printed scaffolds whereas excellent cell adhesion is recovered after application of a gelatin methacrylamide coating. With this novel class of UV-reactive precursors unprecedented hydrogel processing avenues are opened.

Solid State Packing and Photoreactivity of Alkali Metal Salts of trans,trans-Muconate

Three alkali-metal salts of trans,trans-muconate (muco) viz. Li2muco (1), Na2muco (2), and K2muco (3) have been prepared, and the influence of the crystal packing on the solid state photoreactivity has been investigated. Although the C═C bonds of the muco ligands are oriented infinitely parallel in 1, it was found to be photoinert. In contrast, the muco ligands of 2 and 3 in the crystalline state undergo photodimerization yielding cycloocta-3,7-diene-1,2,5,6-tetracarboxylate which has been formed stepwise via the [2 + 2] cycloaddition reaction of a single pair of C═C bonds and subsequent Cope rearrangement. This study demonstrates how the size of the metal ion can influence the crystal packing in metal organic salts.

Following a Photoinduced Reconstructive Phase Transformation and its Influence on the Crystal Integrity: Powder Diffraction and Theoretical Study

In the course of solid-state photoreactions, a single crystal (SC) of the reactant can be transformed into an SC of the product or it can lose crystallinity and become amorphous. In-between these two scenarios exist the reconstructive phase transformations, where upon irradiation, the reactant SC becomes a powder or an SC with increased mosaicity. We present a detailed description of reconstructive photodimerization, where the structural changes are directly correlated with the disintegration process. The kinetics of the reaction is explained by two kinetic regimes, forming an autocatalytic autoinhibition photoreaction set with high quantum yield. In addition, the photoreaction pathways were studied theoretically.

Solid-state photoreactivity of 9-substituted acridizinium bromide salts

A series of substituted acridizinium bromides was studied to determine how substituents affect the regioselectivity of the solid-state [4 + 4] photodimerisation.