Solid-state Photochemical Reactions Research Articles

Shape Dependence of Photoresponsive Molecular Crystals Composed of Naphthyl Acrylic Acid Stimulated by Solid-State [2 + 2] Photocycloaddition

Photomechanical molecular crystals, actuated by solid-state photochemical reactions, manifest a spectrum of mechanical motions upon light exposure, underscoring their prospective integration into the next generation of intelligent materials and devices. Utilizing the solid-state photodimerization of naphthyl acrylic acid as a paradigm, this study delved into the interplay between crystal morphology and reaction dynamics on the photomechanical responses of molecular crystals. Distinct crystal forms—bulk, microrods, and microplates—were cultivated through tailored crystallization conditions. While bulk crystals of naphthyl acrylic acid (NA) underwent shattering and splintering upon UV light exposure, the microplate counterparts displayed unique cracking patterns with fissures yet retained their overall structural integrity. In contrast, NA microrods underwent pronounced bending under identical irradiation conditions. These phenomena are attributed to the efficient lattice reconfiguration stemming from the [2 + 2] cycloaddition photochemical reaction within the crystals. An intermediate fluorescence enhancement was observed across all crystal types upon light exposure. Collectively, our results underscore the pivotal role of crystal shape in dictating photomechanical behavior, thereby heralding novel strategies for developing advanced photomechanical materials.

The origin of [2+2] photocycloaddition reaction in the solid state driving ACQ-to-AIE transformation

The PD reaction mechanism of t-2FSBO and the AIE properties of the two resultant isomers, t-2FPCBO and c-2FPCBO, in both different environments are theoretically investigated using PCM and QM/MM models coupled with the TVCF-based rate theory.

Molecular Twisting Affects the Solid-State Photochemical Reactions of Unsaturated Ketones and the Photomechanical Effects of Molecular Crystals.

Three groups of chalcone derivatives and their analogues involving halogen atoms (X=F, Cl, Br) have been synthesized. Firstly, the nearly planar acyclic chalcone derivatives were inclined to undergo photo-induced stereospecific [2+2] cycloaddition, which triggered the crystals to exhibit macroscopic motions of bending or cracking. In particular, the single-crystal-to-single-crystal transformation happened upon UV irradiation of the crystals, which was helpful for the understanding photomechanical effects. Cyclic 3,4-dihydronaphthalene-based chalcone analogues possess a more twisted conformation, and they tend to undergo trans-cis isomerization. No photomechanical effect was observed for the crystals of the cyclic chalcone analogues due to the lower isomerization rate. The twist degree of chroman-based molecules was in between of the first two, [2+2] cycloaddition and trans-cis isomerization simultaneously took place in crystals. Photo-induced bending and twisting were observed for the crystals of chroman-based chalcone analogues. Therefore, the differences in molecular dihedral angles in α,β-unsaturated ketones were responsible for their photochemical characters and in turn to tune the photomechanical effects. In this work, a bridge between the molecular structures and solid-state photochemical reactions triggered photomechanical crystals is built.

Controllable multiple-step configuration transformations in a thermal/photoinduced reaction

Solid-state photochemical reactions of olefinic compounds have been demonstrated to represent powerful access to organic cyclic molecules with specific configurations. However, the precise control of the stereochemistry in these reactions remains challenging owing to complex and fleeting configuration transformations. Herein, we report a unique approach to control the regiospecific configurations of C = C groups and the intermediates by varying temperatures in multiple-step thermal/photoinduced reactions, thus successfully realizing reversible ring closing/opening changes using a single-crystal coordination polymer platform. All stereochemical transitions are observed by in situ single-crystal X-ray diffraction, powder X-ray diffraction and infrared spectroscopy. Density functional theory calculations allow us to rationalize the mechanism of the synergistic thermal/photoinduced transformations. This approach can be generalized to the analysis of the possible configuration transformations of functional groups and intermediates and unravel the detailed mechanism for any inorganic, organic and macromolecular reactions susceptible to incorporation into single-crystal coordination polymer platforms.

Isolation of elusive cyclobutane ligands via a template-assisted photochemical [2 + 2] cycloaddition reaction and their utility in engineering crystalline solids

Selective examples of isolation of pure cyclobutane compounds via solid-state photochemical reactions of cocrystals, and their utility in engineering crystalline solids are discussed.

Photomechanical Organic Crystals as Smart Materials for Advanced Applications.

Photomechanical molecular crystals are receiving much attention due to their efficient conversion of light into mechanical work and advantages including faster response time; higher Young's modulus; and ordered structure, as measured by single-crystal X-ray diffraction. Recently, various photomechanical crystals with different motions (contraction, expansion, bending, fragmentation, hopping, curling, and twisting) are appearing at the forefront of smart materials research. The photomechanical motions of these single crystals during irradiation are triggered by solid-state photochemical reactions and accompanied by phase transformation. This Minireview summarizes recent developments in growing research into photoresponsive molecular crystals. The basic mechanisms of different kinds of photomechanical materials are described in detail; recent advances in photomechanical crystals for promising applications as smart materials are also highlighted.

Reversible Photolysis of Nitrosobenzene cis-Dimer Monitored In Situ by Single Crystal Photocrystallography

A single crystal of the cis-dimer of nitrosobenzene was directly observed by photocrystallography to transition to a pair of monomers and reversibly redimerize. The remarkable displacement of the nitrogen atoms within the crystal—moving a total distance of 2.97(5) A for the two atoms—suggests that the breadth of solid-state photochemical reaction systems susceptible to X-ray diffraction studies need not be limited to those with very small atomic displacements.

有機結晶のキラリティーを利用した不斉合成法の開発

Asymmetric synthesis from achiral starting materials using only crystal chirality under absolutely achiral conditions-that is, absolute asymmetric synthesis-has been investigated by many methods, including solid-state photochemical reactions, asymmetric reactions using frozen chirality, and dynamic crystallization (total spontaneous resolution). Dynamic crystallization using racemic conglomerate crystals involved that an enantiomerically enriched solid state could be achieved through crystallization from a solution in which chiral molecules could rapidly racemize. Many such examples resulted in total optical resolution by deracemization, selectively leading to single-handed molecules. Furthermore, a combined methodology for generating a chiral center from achiral materials, involving dynamic crystallization or attrition-enhanced deracemization, was recently developed. These examples demonstrate the high potential of this new category of absolute asymmetric synthesis.

Solid-State Photochemical Reaction of Multisubstituted Thymine Derivatives

Solid-state photochemical reactions in crystals, known as topochemical reactions, are solvent-free green chemical reactions that produce stereospecific molecules. The photoreaction of thymine is interesting because the dimeric photoproduct can form four types of stereoisomers and when the dimer is formed in DNA helices it can cause skin cancers. We investigated the photoreaction of five multisubstituted thymine derivatives in the solid-state, which were designed with crystal engineering concepts to promote π–π stacking of benzene rings in the crystal. Powder X-ray diffraction analysis revealed that a para-substituted bis-thymine derivative was aligned along the c axis in the crystal and was susceptible to topochemical reaction to form a polymer, as previously reported. Ortho- and meta-substituted bis-thymine derivatives and a tetrakis-substituted derivative were found to be topochemically unreactive using both gel permeation chromatography (GPC) and X-ray crystal structural analysis. The tris-substituted ...

Analysis of reaction kinetics in the photomechanical molecular crystal 9-methylanthracene using an extended Finke–Watzky model

In order to develop an improved description of the photomechanical response of 9-methylanthracene (9MA) microcrystals, a detailed study of its solid-state photochemical reaction kinetics is performed. The reaction progress is monitored through the decrease in absorption of an optically microcrystalline thin film. The evolution of the time-dependent photoluminescence during the reaction is also measured. Both the photochemical reaction and nonradiative relaxation rates increase as more photoproduct is formed. In order to analyze the data, an extended version of the Finke-Watzky kinetic model for photochemical reactions is derived, denoted the FW-P model. This extended version enables a systematic analysis of photochemical reaction kinetics in solid-state molecular systems at varying levels of approximation. The FW-P model describes the non-exponential decrease in reactant and also correctly predicts the magnitude of the observed decrease in photoluminescence lifetime over the course of the reaction. The lifetime analysis is complicated by the fact that the microcrystalline 9MA sample contains multiple emitting species, and the extended FW-P model fails to capture the exact dependence of the photoluminescence on product formation. Analysis of the 9MA data indicates that both the photodimerization and the nonradiative relaxation rates can be accelerated by a factor of 10 over the course of the reaction. The results in this paper demonstrate that autocatalytic photodimerization kinetics are present in crystalline 9MA and may influence its photomechanical response.

Microbelts and flower-like particles of hexakis-(4-(5-styryl-1,3,4-oxazodiazol-2-yl)-phenoxy)-cyclotriphosphazene: self-assembly and photoreaction

Recently, we have reported the self-assembly of nanobelts and microbelts originating from the organic–inorganic hybrid molecule hexakis-(4-(5-phenyl-1,3,4-oxazodiazol-2-yl)-phenoxy)-cyclotriphosphazene (HPCP) by a simple solution method. Inspired by [2 + 2] photodimerization, our group has further attempted to verify the proposed self-assembly mechanism of oxadiazole-containing cyclotriphosphazene by solid-state photochemical reaction. We modified the molecular structure of HPCP, introducing a vinyl group into it to obtain a new oxadiazole-containing cyclotriphosphazene, hexakis-(4-(5-styryl-1,3,4-oxazodiazol-2-yl)-phenoxy)-cyclotriphosphazene (HSCP). The microbelts and flower-like particles of HSCP were self-assembled through a simple solvent exchange process by exploiting the π–π interactions between neighboring HSCP molecules as the driving force. The as-prepared materials were capable of [2 + 2] photodimerization and shape maintenance, as well as forming insoluble fluorescent materials. The self-aggregating and photoreaction properties of HSCP were characterized by UV-vis, FESEM, TEM, 1H-NMR, etc.

The interplay between hydrogen bonding and π-π stacking interactions in the crystal packing of N1-thyminyl derivatives, and implications for the photo-chemical [2π + 2π]-cycloaddition of thyminyl compounds

The solid-state photo-chemical dimerisation of thyminyl derivatives occurs when two thyminyl units are aligned in such a way that the olefinic moieties are separated by a distance of less than 4.2 Å. When irradiated with >270 nm UV, the thyminyl olefinic groups undergo [2π + 2π]-cycloaddition to form a dimeric cyclobutane derivative. However, the design and execution of [2π + 2π]-cycloaddition reactions can be challenging due to the requirement to produce molecular crystals with the necessary olefinic alignment. In this investigation, the crystallographic and solid-state photo-chemical reactions of six N1-thyminyl derivatives are studied. Only one derivative, thyminyl propanamide (), was found to undergo [2π + 2π]-cycloaddition in the crystalline state. As such, quantum chemical methods were employed to study the photo-chemical transition states of the derivatives, as well as the strengths of typical intermolecular interactions that were observed in their crystal structures (such as π-π stacking between the thyminyl rings, Watson and Crick style hydrogen bonding and hydrogen bonding between functional groups of N1 substituents). These results were used to rationalise the solid-state photo-reactivity of more complex bis-thyminyl monomers.

Azide photochemistry for facile modification of graphitic surfaces: preparation of DNA-coated carbon nanotubes for biosensing

A facile, two-step method for chemically attaching single-stranded DNA to graphitic surfaces, represented here by carbon nanotubes, is reported. In the first step, an azide-containing compound, N-5-azido-nitrobenzoyloxy succinimide (ANB-NOS), is used to form photo-adducts on the graphitic surfaces in a solid-state photochemical reaction, resulting in active ester groups being oriented for the subsequent reactions. In the second step, pre-synthesized DNA strands bearing a terminal amine group are coupled in an aqueous solution with the active esters on the photo-adducts. The versatility of the method is demonstrated by attaching pre-synthesized DNA to surfaces of carbon nanotubes in two platforms—as vertically-aligned multi-walled carbon nanotubes on a solid support and as tangled single-walled carbon nanotubes in mats. The reaction products at various stages were characterized by x-ray photoelectron spectroscopy. Two different assays were used to check that the DNA strands attached to the carbon nanotubes were able to bind their partner strands with complementary base sequences. The first assay, using partner DNA strands tethered to gold nanoparticles, enabled the sites of DNA attachment to the carbon nanotubes to be identified in TEM images. The second assay, using radioactively labelled partner DNA strands, quantified the density of functional DNA strands attached to the carbon nanotubes. The diversity of potential applications for these DNA-modified carbon-nanotube platforms is exemplified here by the successful use of a DNA-modified single-walled carbon-nanotube mat as an electrode for the specific detection of metal ions.

Photoinduced Rearrangement of Aromatic N-Chloroamides to Chloroaromatic Amides in the Solid State: Inverted ΠN–ΣN Occupational Stability of Amidyl Radicals

We report a solid-state photochemical rearrangement reaction by which aromatic N-chloroamides exposed to UV light or sunlight are rapidly and efficiently converted to chloroaromatic amides. The course, the intermediate (nascent chlorine vs dichlorine) and the outcome of the reaction depend on the excitation (exposure time, wavelength, and intensity) and on inherent structural factors (the directing role of the substituents and, as demonstrated by the different reactivity of two polymorphs of N-chlorobenzanilide, the supramolecular structure). The photolysis of the chloroamides provides facile photochemical access to arylamidyl radicals as intermediates, which in the absence of strong hydrogen bond donors are stabilized in the reactant crystals by C-H/N-Cl···π interactions, thus, providing insight into their structure and chemistry. Thorough theoretical modeling of the factors determinant to the stability and the nature of the spin-hosting orbital evidenced that although the trans-Π(||) state (Np spin) of the amidyls is normally preferred over the trans-Σ(⊥) configuration (Nsp(2) spin), stabilization by aromatic conjugation, steric and geometry factors, as well as by electronic effects from the substituents can decrease the Π-Σ gap in these intermediates significantly, resulting in similar and, in the case of the orthogonal amide-phenyl disposition, even reversed population of the unpaired electron in the two orbitals. Quantitative correlation established that the inverted occupational spin stability and the Π(N)-Σ(N) crossover are collectively facilitated by the conformation, valence angle, and disposition of the amide group relative to the aromatic system. The stabilization and detection of a trans-Σ(⊥) radical was experimentally accomplished by steric locking of the orthogonal trans-amide conformation with double ortho-tert-butyl substitution at the phenyl ring. The effects of the single para-phenyl substituents on the relative occupational stability of the arylamidyl radical states point out to non-Hammett behavior. By including cumulative electronic effects from multiple substitutions, four distinct families of the aromatic amidyl radicals were identified. The Π(∥) state is the most stable structure of the N-phenylacetamidyl radical and of most of the substituted arylamidyls, although the Σ(⊥) and Π(⊥) states can also be stabilized by introducing tert-butyl and nitro groups, respectively.

Smartly designed photoreactive silica nanoparticles and their reactivity

Monodisperse, colloidal silica nanoparticles (NPs) are being widely investigated due to a variety of applications in various fields of chemistry. Many works utilize incorporation of various functional groups to silica NPs for their further modifications. However, at present no benzophenone (BPh) or phenyl azide (PA) containing silica NPs exist. Upon UV irradiation BPh and PA form highly reactive species that react with any organic material. Here we present a convenient method for the preparation of novel hybrid photoreactive silica NPs (denoted as SiO2@photoreactive group) prepared by co-condensation of photoreactive organosilanes and tetraethyl orthosilicate (TEOS) to obtain SiO2@PA and SiO2@BPh NPs. The reactivity of these two types of silica NPs is compared to that of perfluorinated phenyl azide (PFPA) based SiO2 NPs. The reactivity evaluation is carried out by the reaction of the three types of SiO2 NPs with highly inert poly(2-chloro-paraxylelene) films. It is found that, in contrast to what is stated in the literature, PA is much more reactive than PFPA, when dealing with solid state photochemical reactions. Next, photoreactive silica NPs on polymer films are used as an intermediate functional phase for a second modification step using silane-based chemistry. A successful incorporation of amine functionality onto silica NPs is achieved by their reaction with 3-aminopropyltriethoxysilane (APTES) and is verified by fluorescence microscopy. This strategy provides a general and versatile route to efficient functionalization of silica by light.

2-Methoxy-3,4-diphenylphenol

The title compound, C19H16O2, was isolated as the major product after the solid-state photochemical reaction of 2-meth­oxy-4,4-diphenyl­cyclo­hexa-2,5-dienone. The dihedral angles between the central ring and pendant benzene rings are 60.76 (6) and 51.64 (6)°. The O—C vector of the meth­oxy group is almost perpendicular to the plane of the central ring as indicated by the C—C—O—C torsion angle of 94.89 (18)°. Hydrogen-bonded dimers are formed in the crystal structure via O—H⋯O inter­actions. The data were collected at room temperature on a Bruker SMART X2S diffractometer in the automated mode and processed manually thereafter.

Bridging protein crystallography and chemistry: structural insight into the O-GlcNAc modification and the structure-inspired design of chemical probes

The history of solid-state reactions goes back to the nineteenth century, however it was considered as “nature curiosity”. The first and most intensive investigated type of solid-state reactions was photochemical reactions. The work done at the Weizmann Institute of Science revealed the well-known “topochemical rules” that are being used also today. Solid-state thermal reactions were neglected and only few cases have been studied. The advantages of solidstate reactions over reactions carried out in solutions are the specificity of the reactions. Much work was devoted to the search for chemical systems that can undergo solid-state reactions, mainly photochemical reactions. In the beginning of the nineties of the last century effort was devoted to use solid-state photochemistry to enhance asymmetric syntheses. Recently the use of templates for solid-state photochemical reactions was successfully demonstrated. In the lecture, historical points in solid-state chemical reactions will be mentioned followed by significant contributions to the subject that will be described. Examples of the work done in our group on thermally activated solidstate reactions, photochemical reactions in neat compounds, and photochemical reactions in solid inclusion compounds will be shown. Important reactions are those that show single-crystal to single-crystal transformations. Those reactions enable monitoring of structural changes during the reaction as well as observing other interesting chemical and physical events. The most interesting systems will be described.

Photoinduced hydrogen atom abstraction in N-(adamantyl)phthalimides: structure–reactivity study in the solid state

Adamantyl-functionalized phthalimides were synthesized and the probability of intramolecular photochemical hydrogen atom abstraction in the solid state analyzed by X-ray crystallographic analyses. These analyses and solid-state photolyses showed that the parameters determining photochemical reactivity for typical carbonyl compounds in the solid state can also be extended to phthalimides. Only N-(2-adamantyl)phthalimide underwent a solid-state photochemical reaction, which is the first example in the phthalimide series. This reaction is regio- and stereoselective, resulting in an endo-alcohol. On the other hand, the photoreaction of N-(2-adamantyl)phthalimide in solution gives an exo-alcohol as the main product together with an endo-alcohol and a benzazepindione.

Pump–probe spectroscopy and circular dichroism of nanocrystalline benzophenone—towards absolute kinetic measurements in solid state photochemical reactions

Nanocrystals suspended in water can be used to record steady state and pump-probe absorption spectra, which should be useful for the study of excited states and reactive intermediates in the solid state.

X-ray crystallographic analysis of N, N-diallylcoumarincarboxamides and the solid-state photochemical reaction

X-ray crystallographic analysis and the photochemical aspects of N, N-diallylcoumarincarboxamides were investigated. Irradiation of the corresponding amides promoted stereoselective intramolecular cyclobutane formation exclusively. The solid-state photoreaction of the coumarinamide without substituent on the 4-position proceeded in a crystal-to-crystal manner. On the other hand, photolysis of the amide possessing a methyl group at the 4-position also effected 2+2 cycloaddition; however, the reaction proceeded much slower. The difference in the reactivity was explainable on the basis of the molecular conformation in the crystal lattice.