Single-Crystal-to-Single-Crystal Photosynthesis of Supramolecular Organoboron Polymers with Dynamic Effects.

The solid-state synthesis of single-crystalline organic polymers, having functional properties, remains an attractive and developing research area in polymer chemistry and materials science. However, light-triggered topochemical synthesis of crystalline polymers comprising an organoboron backbone has not yet been reported. Here, we describe an intriguing example of single-crystal-to-single-crystal (SCSC) rapid photosynthesis (occurs on a seconds-scale) of two structurally different linear organoboron polymers, driven by environmentally sustainable visible/sun light, obtained from the same monomer molecule. A newly designed Lewis acid-base type molecular B ← N organoboron adduct (consisting of an organoboron core and naphthylvinylpyridine ligands) crystallizes in two solid-state forms featuring the same chemical structure but different 3D structural topologies, namely, monomers 1 and 2. The solvate molecule-free crystals of 1 undergo topochemical photopolymerization via an unusual olefin-naphthyl ring [2 + 2] cyclization to yield the single crystalline [3]-ladderane polymer 1P growing along the B ← N linkages, accompanied by instantaneous and violent macroscopic mechanical motions or photosalient effects (such as bending-reshaping and jumping motions). In contrast, visible light-harvesting single crystals of 2 quantitatively polymerize to a B ← N bond-stabilized polymer 2P in a SCSC fashion owing to the rapid [2 + 2] cycloaddition reaction among olefin double bonds. Such olefin bonds in the crystals of 2 are suitably preorganized for photoreaction due to the presence of solvate molecules in the crystal packing. Single crystals of 2 also show photodynamic jumping motions - in response to visible light but in a relatively slower fashion than the crystals of 1. In addition to SCSC topochemical polymerization and dynamic motions, both monomer crystals and their single-crystalline polymers feature green emissive and short-lived room-temperature phosphorescence properties upon excitation with visible-light wavelength.

Modular Synthesis of Azines Bearing a Guanidine Core from N-Heterocyclic Carbene (NHC)-Derived Selenoureas and Diazo Reagents.

N-Heterocyclic carbene (NHC)-derived selenoureas comprise a fundamentally important class of NHC derivatives, with key applications in coordination chemistry and the determination of NHC electronic properties. Considering the broad reactivity of chalcogen-containing compounds, it is surprising to note that the use of NHC-derived selenoureas as organic synthons remains essentially unexplored. The present contribution introduces a novel, straightforward transformation leading to azines bearing a guanidine moiety, through the reaction of a wide range of NHC-derived selenoureas with commercially available diazo compounds, in the presence of triphenylphosphine. This transformation offers a new approach to such products, having biological, materials chemistry, and organic synthesis applications. The guanidine-bearing azines are obtained in excellent yields, with all manipulations taking place in air. A reaction mechanism is proposed, based on both experimental mechanistic findings and density functional theory (DFT) calculations. A one-pot, multicomponent transesterification reaction between selenoureas, α-diazoesters, alcohols, and triphenylphosphine was also developed, providing highly functionalized azines.

Two-Dimensional Silver-Chalcogenolate-Based Cluster-Assembled Material: A p-type Semiconductor.

We have synthesized and characterized a new two-dimensional honeycomb architecture resembling a single-layer of atomically precise silver cluster-assembled material (CAM), [Ag12(StBu)6(CF3COO)6(4,4'-azopyridine)3] (Ag12-azo-bpy). The interlayer noncovalent van der Waals interactions within the single-crystals were successfully disrupted, leading to the creation of this unique structure. The optimized Ag12-azo-bpy CAM demonstrates a valence band that is localized on the Ag12 cluster node situated near the Fermi energy level. This localization induces electron injection from the linker to the cluster node, facilitating efficient charge transportation along the plane. Exploiting this single-layer structure as a distinctive platform for p-type channel material, it was employed in a field-effect transistor configuration. Remarkably, the transistor exhibits a high hole mobility of 1.215 cm2 V-1 s-1 and an impressive ON/OFF current ratio of ∼4500 at room-temperature.

Two Structurally Different Polymers from a Single Monomer.

We designed and synthesized a malonamide-derived monomer, containing azide and alkyne units, for topochemical polymerization to yield nylon (n,3). This monomer on crystallization gave two concomitant polymorphs M1 and M2. Both the polymorphs show crystal packings that are suitable for topochemical azide-alkyne cycloaddition polymerization. On heating, polymorph M1 reacts regiospecifically to give 1,4-disubstituted-1,2,3-triazolyl-linked polymer, whereas polymorph M2 yields 1,5-disubstituted-1,2,3-triazolyl-linked polymer regiospecifically. In the case of polymorph M1, polymerization proceeds perpendicular to the hydrogen bonding direction, whereas in M2, the reaction occurs along the hydrogen bonding direction. This results in the two structurally different polymers having distinct topologies. These single-crystal-to-single-crystal polymerizations allowed us to study their structure at atomic resolution by single-crystal X-ray diffraction. This is the first report on the topochemical synthesis of two structurally isomeric polymers from a single monomer.

The New Ag-S Cluster [Ag50S13(StBu)20][CF3COO]4 with a Unique hcp Ag14 Kernel and Ag36 Keplerian-Shell-Based Structural Architecture and Its Photoresponsivity.

In metal nanoclusters (NCs), the kernel geometry and the nature of the surface protecting ligands are very crucial for their structural stability and properties. The synthesis and structural elucidation of Ag NCs is challenging because the zerovalent oxidation state of Ag is very reactive and prone to oxidization. Here, we report the NC [Ag50S13(StBu)20][CF3COO]4 with a hexagonal close-packed (hcp) cagelike Ag14 kernel. A truncated cubic shell and an octahedral shell encapsulate the hcp-layered kernel via an interstitial S2- anionic shell to form an Ag36 Keplerian outer shell of the NC. A theoretical study indicates the stability of this NC in its 4+ charge state and the charge distribution between the kernel and Keplerian shell. The unprecedented electronic structure facilitates its application toward sustainable photoresponse properties. The new insights into this novel Ag NC kernel and Keplerian shell structure may pave the way to understanding the unique structure and developing electronic structure-based applications.

Visible Light-fueled Mechanical Motions with Dynamic Phosphorescence Induced by Topochemical [2+2] Reactions in Organoboron Crystals.

In the quest for essential energy solutions towards an ecological friendly future, the transformation of visible light/solar energy into mechanical motions in metal-free luminescent crystals offers a sustainable choice of smart materials for lightweight actuating, and all-organic electronic devices. Such green energy-triggered photodynamic motions with room temperature phosphorescence (RTP) emission in molecular crystals have not been reported yet. Here, we demonstrate three new stoichiometrically different Lewis acid-base molecular organoboron crystals (PS1, PS2, and PS3), which exhibit rapid photosalient effects (ballistic splitting, moving, and jumping) under both ultraviolet (UV) and visible light associated with quantitative single-crystal-to-single-crystal (SCSC) [2+2] cycloaddition of preorganized olefins. Furthermore, these systems respond to sunlight and mobile (white) flashlight with a complete SCSC transformation in a relatively slow fashion. Remarkably, all PS1, PS2, and PS3 crystals display visible light-promoted dynamic green RTP as their emission peaks promptly blue-shift, due to instantaneous photomechanical effects. Time-dependent structural mapping of intermediate photoproducts during fast SCSC [2+2] photoreaction, by X-ray photodiffraction, reveals a rationale for the origin of these photodynamic motions associated with rapid topochemical transformations. The reported light-driven behavior (mechanical motions, dynamic phosphorescence, and topochemical reactivity), is considered advantageous for the strategic design of stimuli-responsive multi-functional crystalline materials.

Photomechanical Motions in Organoboron-Based Phosphorescent Molecular Crystals Driven by a Crystal-State [2 + 2] Cycloaddition Reaction.

Photoluminescent molecular crystals integrated with the ability to transform light energy into macroscopic mechanical motions are a promising choice of materials for both actuating and photonic devices. However, such dynamic photomechanical effects, based on molecular organoboron compounds as well as phosphorescent crystalline materials, are not yet known. Here we present an intriguing example of photomechanical molecular single crystals of a newly synthesized organoboron containing Lewis acid-base molecular adduct (BN1, substituted triphenylboroxine and 1,2-di(4-pyridyl)ethylene) having a capsule shape molecular geometry. The single crystals of BN1 under UV light exhibit controllable rapid bending-shape recovery, delamination, violent splitting-jumping, and expanding features. The detailed structural investigation by single-crystal X-ray diffraction and 1H NMR spectroscopy reveals that the photosalient behavior of the BN1 single crystals is driven by a crystal-to-crystal [2 + 2] cycloaddition reaction, supported by four donor-acceptor type B←N bonds. The instant photomechanical reaction in the BN1 crystals occurs under UV on account of sudden release of stress associated with the strained molecular geometry, significant solid-state molecular movements (supramolecular change), and cleavage of half intermolecular B←N linkages to result in a complete photodimerized single-crystalline product via the existence of two other intermediate photoproducts. In addition, the BN1 crystals display short-lived room temperature phosphorescence, and the photodynamic events are accompanied by the enhancement of their phosphorescence intensity to yield the photoproduct. Interestingly, the molecular crystals of the final photoproduct polymerize at ambient conditions when recrystallized from the solution forming a 2D supramolecular crystalline polymer stabilized by the retention of all B←N coordination modes.

Azide-Alkyne Interactions: A Crucial Attractive Force for Their Preorganization for Topochemical Cycloaddition Reaction.

A new class of attractive intermolecular interaction between azide and ethynyl structural entities in a wide range of molecular crystals is reported. This interaction was systematically evaluated by using 11 geometrically different structural motifs that are preorganized to direct a solid-state topochemical azide-alkyne cycloaddition (TAAC) reaction. The supramolecular features of the azide-alkyne interaction were mapped by various crystallographic and quantum chemical approaches. Topological analysis shows the noticeable participation of electron density in the azide⋅⋅⋅alkyne interactions. Interestingly, reorientation of the atomic polarizabilities in vicinal azide and alkyne groups upon interaction in crystals favors soft orbital-guided TAAC reactions. Moreover, various solid-state and gas-phase energy decomposition methods of individual azide⋅⋅⋅alkyne interactions summarize that the strength (varies from -5.7 to -30.1 kJ mol-1 ) is primarily guided by the dispersion forces with a influencing contribution from the electrostatics.

Synthesis of Carbene-Metal-Amido (CMA) Complexes and Their Use as Precatalysts for the Activator-Free, Gold-Catalyzed Addition of Carboxylic Acids to Alkynes.

A straightforward synthetic protocol leading to carbene-metal-amido (CMA) complexes (metal=Au, Cu) using a mild base and an environmentally desirable solvent (EtOH) has been explored, with a focus on complexes bearing backbone-substituted N-heterocyclic carbene (NHC) ligands, including BIAN-NHCs (BIAN=bis(imino)acenaphthene). The novel CMAs were structurally characterized, and gold-based CMAs bearing diverse NHCs were screened as simple, Brønsted-basic precatalysts. The readily accessible complexes display high catalytic activity in the intermolecular and intramolecular hydrocarboxylation of internal alkynes and alkynoic acids respectively, while the screening reveals the ancillary ligand effect of NHCs in these catalytic systems.

Bridging the Bays, Both Ways: A Janus Butterfly-Shaped Intense NIR-Emitting Terrylene Diimide.

Molecules with intense near-IR (NIR) emission are beneficial for modern applications such as night vision, bio-imaging etc. However, elaborate synthetic manipulations make them demanding to accomplish. Herein, we present a simple yet exciting strategy to obtain novel Janus butterfly-shaped terrylene diimide derivatives with carbazole wings having absorption and intense emission in the NIR. Especially, unsymmetrically substituted terrylene diimides (TDIs) have been observed to have impressive emission quantum yields (up to 93 %), highest for this class of compounds. Minimal structural distortion as evidenced from structural characterization has been shown to correlate with these observations. Also, a novel two-tiered TDI-carbazole having an intense emission at 897 nm is also reported. Our strategy demonstrates that efficient near-IR luminophores can be achieved via precise functionalization.

Topochemical Postulates: Are They Relevant for Topochemical Reactions Occurring at Elevated Temperatures?

A rigid inositol-derived monomer functionalized with azide and alkyne as the complementary reactive groups (CRGs) crystallized as three distinct polymorphs I-III. Despite the unsuitable orientation of CRGs in the crystals for complete polymerization, all the three polymorphs underwent regiospecific and quantitative topochemical azide-alkyne cycloaddition (TAAC) polymerization upon heating to yield three different polymorphs of 1,2,3-triazol-1,4-diyl-linked-poly-neo-inositol. The molecules in these polymorphs exploit the weak intermolecular interactions, free space in the crystal lattice, and heat energy for their large and cooperative molecular motion to attain a transient reactive orientation, ultimately leading to the regiospecific TAAC reaction yielding distinct crystalline polymers. This study cautions that the overreliance on topochemical postulates for the prediction of topochemical reactivity at high temperatures could be misleading.

Tuning the Regioselectivity of Topochemical Polymerization through Cocrystallization of the Monomer with an Inert Isostere.

Regiochemistry of topochemical reactions depends on the crystal packing and biasing the regiochemistry necessitates precise crystal engineering. The pristine crystals of monomer 1 upon topochemical azide-alkyne cycloaddition (TAAC) reaction give a 1 : 1 blend of 1,4- and 1,5-triazole-linked polymers due to the presence of two self-sorted reactive conformers in the crystal. We designed a binary isomorphous cocrystal of monomer 1 and a structurally similar dummy molecule 2 to limit the number of reactive conformers of 1 to one and thus to get one type of polymer. Equimolar solution of 1 and 2 in chloroform-acetone mixture gave two 1 : 1 cocrystals Co-I and Co-II. The Co-II, a chloroform adduct, on heating undergoes desolvation and polymorphic transition to Co-I. Co-I is isomorphic to 1 and 2 and possess self-sorted arrays of 1 and 2. Heating Co-I results in the TAAC polymerization giving 1,4-triazolyl-linked polymer of 1 selectively, showing the power of crystal engineering in regiocontrol.

Continuous Flow Synthesis of [Au(NHC)(Aryl)] (NHC=N-Heterocyclic Carbene) Complexes.

The use of weak and inexpensive bases has recently opened promising perspectives towards the simpler and more sustainable synthesis of Au(I)-aryl complexes with valuable applications in catalysis, medicinal chemistry, and materials science. In recent years, continuous manufacturing has shown to be a reliable partner in establishing sustainable and controlled process scalability. Herein, the first continuous flow synthesis of a range of Au(I)-aryl starting from widely available boronic acids and various [Au(NHC)Cl] (NHC=N-heterocyclic carbene) complexes in unprecedentedly short reaction times and high yields is reported. Successful synthesis of previously non- or poorly accessible complexes exposed fascinating reactivity patterns. Via a gram-scale synthesis, convenient process scalability of the developed protocol was showcased.

Role of Ligand on Photophysical Properties of Nanoclusters with fcc Kernel: A Case Study of Ag14(SC6H4X)12(PPh3)8 (X = F, Cl, Br).

The structure-property correlation of a series of silver nanoclusters (NCs) is essential to understand the origin of photophysical properties. Here, we report a series of face-centered cubic (fcc)-based silver NCs by varying the halogen atom in the thiolate ligand to investigate the influence of the halide atoms on the electronic structure. These are {Ag14(FBT)12(PPh3)8·(solvent)x} (NC-1), Ag14(CBT)12(PPh3)8 (NC-2), and Ag14(BBT)12(PPh3)8 (NC-3), where 4-fluorothiophenol (FBT), 4-chlorothiophenol (CBT), and 4-bromothiophenol (BBT) have been utilized as thiolate ligands, respectively. Interestingly, the optical and electrochemical bandgap values of these NCs nicely correlated with the electronic effect of the halides, which is governed by the intracluster and interclusters π-π interactions. These clusters are emissive at room temperature and the luminescence intensity increases with the lowering of temperature. The short lifetime data suggest that the emission is predominantly originating due to the interband relaxation (d → sp) of the Ag cores. Femtosecond transient absorption (TA) spectra revealed similar types of decay profiles for NC-2 and NC-3 and longer decay time for NC-2. The relaxation dominates the decay profile to the surface states and most of the excited-state energy dissipates via this process. This supports the molecular-like dynamics of these series of NCs with an fcc core. This overview shed light on an in-depth understanding of ligand's role in luminescence and transient absorption spectra.

Lead-Free, Water-Stable A3 Bi2 I9 Perovskites: Crystal Growth and Blue-Emitting Quantum Dots [A=CH3 NH3 + , Cs+ , and (Rb0.05 Cs2.95 )+ ].

Despite the great success in the increase in the power conversion efficiency of lead halide perovskite solar cells, the toxicity of lead and the unstable nature of the materials are still major concerns for their wider implementation at the industrial level. Herein, large-size single crystals (SCs) are developed in HI solution by using a temperature lowering method and nanocrystals (NCs) of A3 Bi2 I9 perovskites [where A=CH3 NH3 + (MA)+ , Cs+ , and (Rb0.05 Cs2.95 )+ ] are formed in ethanol (EtOH) and toluene (TOL). The stability of A3 Bi2 I9 perovskite is investigated by immersing the SCs for 24 h and pellets for 12 h in water. Moreover, the A3 Bi2 I9 perovskite NCs displays a promising photoluminescence quantum yield of 17.63 % and a long lifetime of 8.20 ns.

Larvicidal Activities of 2-Aryl-2,3-Dihydroquinazolin -4-ones against Malaria Vector Anopheles arabiensis, In Silico ADMET Prediction and Molecular Target Investigation.

Malaria, affecting all continents, remains one of the life-threatening diseases introduced by parasites that are transmitted to humans through the bites of infected Anopheles mosquitoes. Although insecticides are currently used to reduce malaria transmission, their safety concern for living systems, as well as the environment, is a growing problem. Therefore, the discovery of novel, less toxic, and environmentally safe molecules to effectively combat the control of these vectors is in high demand. In order to identify new potential larvicidal agents, a series of 2-aryl-1,2-dihydroquinazolin-4-one derivatives were synthesized and evaluated for their larvicidal activity against Anopheles arabiensis. The in silico absorption, distribution, metabolism, excretion, and toxicity (ADMET) properties of the compounds were also investigated and most of the derivatives possessed a favorable ADMET profile. Computational modeling studies of the title compounds demonstrated a favorable binding interaction against the acetylcholinesterase enzyme molecular target. Thus, 2-aryl-1,2-dihydroquinazolin-4-ones were identified as a novel class of Anopheles arabiensis insecticides which can be used as lead molecules for the further development of more potent and safer larvicidal agents for treating malaria.

Energy frameworks and a topological analysis of the supramolecular features in in situ cryocrystallized liquids: tuning the weak interaction landscape via fluorination.

Weak intermolecular interactions observed in crystalline materials are often influenced or forced by stronger interactions such as classical hydrogen bonds. Room temperature liquids offer a scenario where such strong interactions are absent so that the role and nature of the weak interactions can be studied more reliably. In this context, we have analyzed the common organic reagent benzoyl chloride (BC) and a series of its fluorinated derivatives using in situ cryocrystallography. The intermolecular interaction energies have been estimated and their topologies explored using energy framework analysis in a series of ten benzoyl chloride analogues, which reveal that the ππ stacking interactions serve as the primary building blocks in these crystal structures. The crystal packing is also stabilized by a variety of interaction motifs involving weak C-HO/F/Cl hydrogen bonds and FF, FCl, and ClCl interactions. It is found that fluorination alters the electrostatic nature of the benzoyl chlorides, with subsequent changes in the formation of different weak interaction motifs. The effects of fluorination on these weak intermolecular interactions have been systematically analyzed further via detailed inputs from a topological analysis of the electron density and Hirshfeld surface analysis.

Analysis of COF-300 synthesis: probing degradation processes and 3D electron diffraction structure.

Although COF-300 is often used as an example to study the synthesis and structure of (3D) covalent organic frameworks (COFs), knowledge of the underlying synthetic processes is still fragmented. Here, an optimized synthetic procedure based on a combination of linker protection and modulation was applied. Using this approach, the influence of time and temperature on the synthesis of COF-300 was studied. Synthesis times that were too short produced materials with limited crystallinity and porosity, lacking the typical pore flexibility associated with COF-300. On the other hand, synthesis times that were too long could be characterized by loss of crystallinity and pore order by degradation of the tetrakis(4-aminophenyl)methane (TAM) linker used. The presence of the degradation product was confirmed by visual inspection, Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). As TAM is by far the most popular linker for the synthesis of 3D COFs, this degradation process might be one of the reasons why the development of 3D COFs is still lagging compared with 2D COFs. However, COF crystals obtained via an optimized procedure could be structurally probed using 3D electron diffraction (3DED). The 3DED analysis resulted in a full structure determination of COF-300 at atomic resolution with satisfying data parameters. Comparison of our 3DED-derived structural model with previously reported single-crystal X-ray diffraction data for this material, as well as parameters derived from the Cambridge Structural Database, demonstrates the high accuracy of the 3DED method for structure determination. This validation might accelerate the exploitation of 3DED as a structure determination technique for COFs and other porous materials.

Synthesis of N-heterocyclic carbene (NHC)-Au/Ag/Cu benzotriazolyl complexes and their catalytic activity in propargylamide cycloisomerization and carbonyl hydrosilylation reactions.

Carbene-metal-amide (CMA) complexes of gold, silver, and copper have been studied extensively for their photochemical/photocatalytic properties and as potential (pre-)catalysts in organic synthesis. Herein, the design, synthesis, and characterization of five bench-stable Au-, Ag-, and Cu-NHC complexes bearing the benzotriazolyl anion as an amide donor, are reported. All complexes are synthesized in a facile and straightforward manner, using mild conditions. The catalytic activity of the Ag and Cu complexes was studied in propargylamide cycloisomerization and carbonyl hydrosilylation reactions. Both CMA-catalyzed transformations proceed under mild conditions and are highly efficient for a range of propargylamides and carbonyl compounds, respectively, affording the desired corresponding products in good to excellent yields.

Deformation-induced phosphorescence shift in a 2D elastically flexible organic single crystal: role of chalcogen-centered weak interactions.

Mechanically responsive organic luminescent crystals are one of the promising choices of materials for flexible photonic devices. However, the change in phosphorescence emission as a function of the flexibility of a crystal has never been reported. Our current findings demonstrate two-dimensional (2D) and one-dimensional (1D) macroscopic elastic deformability, under mechanical stress, in elastically flexible single crystals of dibenzothiophene, and its brominated derivative, respectively. Unlike the presence of dual fluorescence (FL) and room temperature phosphorescence (RTP) in dibenzothiophene single crystals, the derivative was found to show only RTP. Interestingly, upon elastic deformation, single crystals of the dual emissive dibenzothiophene show a noticeable blue shift (∼20 nm) of RTP emission when compared to their pristine crystals (straight and naturally bent). However, their FL peaks remain nearly unchanged irrespective of the crystal deformation. A hierarchy of structure-elastic functionality to RTP modulation has been quantitatively mapped by rationalizing the role of chalcogen-involved weak interactions.