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We report the application of a Pictet-Spengler reaction to the synthesis of covalent organic frameworks (COFs) using functionalized terephthalaldehydes. The COFs produced show an increased propensity to generate screw dislocations and produce multilayered flakes when compared with other 2D-COFs. Using HRTEM, definitive evidence for screw dislocations was obtained and is presented. The effects on separations using these materials in membranes are also reported.

A seventh blind test of crystal structure prediction has been organized by the Cambridge Crystallographic Data Centre. The results are presented in two parts, with this second part focusing on methods for ranking crystal structures in order of stability. The exercise involved standardized sets of structures seeded from a range of structure generation methods. Participants from 22 groups applied several periodic DFT-D methods, machine learned potentials, force fields derived from empirical data or quantum chemical calculations, and various combinations of the above. In addition, one non-energy-based scoring function was used. Results showed that periodic DFT-D methods overall agreed with experimental data within expected error margins, while one machine learned model, applying system-specific AIMnet potentials, agreed with experiment in many cases demonstrating promise as an efficient alternative to DFT-based methods. For target XXXII, a consensus was reached across periodic DFT methods, with consistently high predicted energies of experimental forms relative to the global minimum (above 4 kJ mol -1 at both low and ambient temperatures) suggesting a more stable polymorph is likely not yet observed. The calculation of free energies at ambient temperatures offered improvement of predictions only in some cases (for targets XXVII and XXXI). Several avenues for future research have been suggested, highlighting the need for greater efficiency considering the vast amounts of resources utilized in many cases., (open access.)

A seventh blind test of crystal structure prediction was organized by the Cambridge Crystallographic Data Centre featuring seven target systems of varying complexity: a silicon and iodine-containing molecule, a copper coordination complex, a near-rigid molecule, a cocrystal, a polymorphic small agrochemical, a highly flexible polymorphic drug candidate, and a polymorphic morpholine salt. In this first of two parts focusing on structure generation methods, many crystal structure prediction (CSP) methods performed well for the small but flexible agrochemical compound, successfully reproducing the experimentally observed crystal structures, while few groups were successful for the systems of higher complexity. A powder X-ray diffraction (PXRD) assisted exercise demonstrated the use of CSP in successfully determining a crystal structure from a low-quality PXRD pattern. The use of CSP in the prediction of likely cocrystal stoichiometry was also explored, demonstrating multiple possible approaches. Crystallographic disorder emerged as an important theme throughout the test as both a challenge for analysis and a major achievement where two groups blindly predicted the existence of disorder for the first time. Additionally, large-scale comparisons of the sets of predicted crystal structures also showed that some methods yield sets that largely contain the same crystal structures., (open access.)

Invited for the cover of this issue are Mubarak Almehairbi, Vikram C. Joshi, Changquan Calvin Sun and Sharmarke Mohamed. The image depicts the digital exploration of the mechanical properties of crystals on specific facets that may be of interest for materials applications by "dialing-in" their stress response. Read the full text of the article at 10.1002/chem.202400779., (© 2024 Wiley-VCH GmbH.)

Dynamic molecular crystals are an emerging class of crystalline materials that can respond to mechanical stress by dissipating internal strain in a number of ways. Given the serendipitous nature of the discovery of such crystals, progress in the field requires advances in computational methods for the accurate and high-throughput computation of the nanomechanical properties of crystals on specific facets which are exposed to mechanical stress. Here, we develop and apply a new atomistic model for computing the surface elastic moduli of crystals on any set of facets of interest using dispersion-corrected density functional theory (DFT-D) methods. The model was benchmarked against a total of 24 reported nanoindentation measurements from a diverse set of molecular crystals and was found to be generally reliable. Using only the experimental crystal structure of the dietary supplement, L-aspartic acid, the model was subsequently applied under blind test conditions, to correctly predict the growth morphology, facet and nanomechanical properties of L-aspartic acid to within the accuracy of the measured elastic stiffness of the crystal, 24.53±0.56 GPa. This work paves the way for the computational design and experimental realization of other functional molecular crystals with tailor-made mechanical properties., (© 2024 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Dynamic covalent chemistry (DCC) has revolutionized the field of polymer science by offering new opportunities for the synthesis, processability, and recyclability of polymers as well as in the development of new materials with interesting properties such as vitrimers and covalent organic frameworks (COFs). Many DCC linkages have been explored for this purpose, but recently, enamine-ones have proven to be promising dynamic linkages because of their facile reversible transamination reactions under thermodynamic control. Their high stability, stimuli-responsive properties, and tunable kinetics make them promising dynamic cross-linkers in network polymers. Given the rapid developments in the field in recent years, this review provides a critical and up-to-date overview of recent developments in enamine-one chemistry, including factors that control their dynamics. The focus of the review will be on the utility of enamine-ones in designing a variety of processable and self-healable polymers with important applications in vitrimers and recyclable closed-loop polymers. The use of enamine-one linkages in crystalline polymers, known as COFs and their applications are also summarized. Finally, we provide an outlook for future developments in this field., (© 2024 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

The discovery of molecular ionic cocrystals (ICCs) of active pharmaceutical ingredients (APIs) widens the opportunities for optimizing the physicochemical properties of APIs whilst facilitating the delivery of multiple therapeutic agents. However, ICCs are often observed serendipitously in crystallization screens and the factors dictating their crystallization are poorly understood. We demonstrate here that mechanochemical ball milling is a versatile technique for the reproducible synthesis of ternary molecular ICCs in less than 30 min of grinding with or without solvent. Computational crystal structure prediction (CSP) calculations have been performed on ternary molecular ICCs for the first time and the observed crystal structures of all the ICCs were correctly predicted. Periodic dispersion-corrected DFT calculations revealed that all the ICCs are thermodynamically stable (mean stabilization energy=-2 kJ mol -1 ) relative to the crystallization of a physical mixture of the binary salt and acid. The results suggest that a combined mechanosynthesis and CSP approach could be used to target the synthesis of higher-order molecular ICCs with functional properties., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Studying single catalyst nanoparticles, during reaction, eliminates averaging effects that are an inherent limitation of ensemble experiments. It enables establishing structure-function correlations beyond averaged properties by including particle-specific descriptors such as defects, chemical heterogeneity and microstructure. Driven by these prospects, several single particle catalysis concepts have been implemented. However, they all have limitations such as low throughput, or that they require very low reactant concentrations and/or reaction rates. In response, we present a nanofluidic device for highly parallelized single nanoparticle catalysis in solution, based on fluorescence microscopy. Our device enables parallel scrutiny of tens of single nanoparticles, each isolated inside its own nanofluidic channel, and at tunable reaction conditions, ranging from the fully mass transport limited regime to the surface reaction limited regime. In a wider perspective, our concept provides a versatile platform for highly parallelized single particle catalysis in solution and constitutes a promising application area for nanofluidics.

Tetracyanobutadiene (TCBD) derivatives of ferrocenyl BODIPYs 2a-2c were designed and synthesized by [2 + 2] cycloaddition-retroelectrocyclization reaction of tetracyanoethylene (TCNE) with meso alkynylated ferrocenyl BODIPYs. The TCBD substituted ferrocenyl BODIPYs were designed in such a way that the distance between the ferrocenyl unit and the TCBD remains constant, whereas the distance between the BODIPY and the TCBD unit varies. The TCBD and BODIPY units were connected directly through a single bond (in 2a), through a phenylacetylene linkage (in 2b) and through a vinyl linkage (in 2c). The photonic and electrochemical properties of ferrocenyl BODIPYs were strongly perturbed by the incorporation of TCBD. The TCBD derivatives 2a-2c show red shifted absorption compared to their precursors 1a-1c. The single crystal structures of TCBD functionalized ferrocenyl BODIPYs 2a and 2c reveal extensive intermolecular hydrogen bonding but lack π-π stacking interactions.

Two organoboron based fluorophores pyrazabole and BODIPY have been designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction and successfully employed for fluoride and cyanide ion sensing. Pyrazabole acts as a fluorimetric sensor, whereas BODIPY acts as a fluorimetric as well as colorimetric sensor for fluoride and cyanide ions with ratiometric response. The photophysical properties of pyrazabole and BODIPY exhibit good electronic communication between triarylborane and pyrazabole/BODIPY. The single crystal X-ray structure of the pyrazabole shows a chair conformation for the pyrazabole core. The packing in pyrazabole and BODIPY shows interesting supramolecular structures. The computational studies show good agreement with the experimental results.

We report the synthesis of meso enyne substituted BODIPYs by the reaction of 8-chloro BODIPY with terminal alkynes under Sonogashira coupling conditions, and by Pd-Cu catalyzed hydroalkynylation reaction of terminal alkynes, across the -C[triple bond, length as m-dash]C- bond of meso alkynylated BODIPYs. The scope of reaction was explored by reacting different meso alkynylated BODIPYs with various terminal alkynes, which results in meso enyne substituted BODIPYs with different substituents. The meso enyne substituted BODIPYs show blue shifted absorption and red shifted emission with large Stokes shift compared to meso alkynylated BODIPYs. The single crystal structures of BODIPYs , , and are reported. Their packing diagram exhibits extensive intermolecular C-Hπ, C-HF hydrogen bonding and ππ stacking interactions, leading to 1D supramolecular frameworks extending into the complex 3D structural frameworks.

The tetraphenylethylene (TPE) substituted BODIPY 2a, and 2,3,3-triphenylacrylonitrile (TPAN) substituted BODIPYs 2b and 2c were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. Their photophysical and electrochemical properties were investigated. The BODIPY 2a exhibits strong D-A interaction with poor fluorescence quantum yield. The BODIPYs 2b and 2c show red-shifted absorption and emission with higher fluorescence quantum yield compared to BODIPY 2a. The photonic properties of BODIPYs 2a-2c were compared with 4-ethynylbenzonitrile substituted BODIPY 3 and phenylacetylene substituted BODIPY 4. The results reveal that the electron donating group at the meso position of BODIPY blue shifts the absorption and emission with decreased fluorescence quantum yield, whereas the electron withdrawing group at the meso position of BODIPY red shifts the absorption and emission with enhanced quantum yields. The single crystal structures of BODIPYs 2a and 2b reflect the planar orientation of meso substituent and the BODIPY core, which leads to close π-π stacking. The extensive π-π stacking and strong donor-acceptor (D-A) interaction makes these BODIPYs AIE inactive. The experimental observations were supported by DFT calculation.

A set of carbazole substituted BODIPYs 2a-2c were designed and synthesized by the Pd-catalysed Sonogashira cross-coupling reaction. The effects of variation in the donor strength of various carbazoles were investigated by photophysical, electrochemical and computational studies. The electronic absorption spectra of BODIPYs 2a and 2c show charge transfer bands, which show red shift in polar solvents. The BODIPYs 2a-2c are highly fluorescent in nonpolar solvents (emission from the localized state) and poorly fluorescent in polar solvents (emission from the charge transfer state). The photophysical and electrochemical studies reveal strong donor-acceptor interaction between carbazole and BODIPY and follows the order 2a > 2c > 2b. The computational calculations show good agreement with the experimental results. The single crystal structures of BODIPYs 2a-2c are reported, which exhibit interesting supramolecular interactions. The packing diagrams of 2a show a zigzag 3D structural arrangement, whereas 2b and 2c show complex 3D structural motifs.

Tetraphenylethene (TPE) substituted phenanthroimidazoles 3a and 3b were designed and synthesized by the Suzuki cross-coupling reaction. They show reversible mechanochromic behavior with contrast colors between sky-blue and yellow green. The powder XRD studies show that destruction of a crystalline state into an amorphous state is responsible for mechanochromism. Hydrogen bonding interaction of a cyano-group in 3b results in enhanced AIE and improved thermal stability.

Different enamines were introduced at the meso position of the BODIPY by catalyst free oxidation of tert-amines and in situ cross coupling with 8-chloro BODIPY. The reaction conditions were optimized to achieve better yields. The reaction works well with aliphatic tert-amines bearing an N-(CH-CH-) backbone. The N-alkyl substituents perturb the optical properties of enamine substituted BODIPYs.

A series of meso arylethynyl BODIPYs (2a-2h) were designed and synthesized by the Pd-catalyzed Sonogashira cross-coupling reaction. The effects of the donor on the photophysical properties of the BODIPYs were explored. The DFT optimized structures and crystal structures show the planar orientation of the donor group with respect to the acceptor BODIPY, which favors a high degree of conjugation and induces strong donor-acceptor interactions. The quenching of fluorescence was correlated with the electron donating strength of the donor. The anthracene, pyrene and triphenylamine were found to have a stronger electron donating ability than the p-methoxyphenyl, phenanthrene, 1-naphthalene, biphenyl, and 2-naphthalene moieties. This was further supported by computational calculations and electrochemical analysis. The single crystal structures of BODIPYs 2d and 2e are reported, which show marvellous supramolecular structures.

meso-Alkynylated ferrocenyl BODIPYs (3-6) with varying conjugation length have been designed, and synthesized using the palladium catalyzed Sonogashira cross-coupling reaction of meso-chloro BODIPY with the corresponding ferrocenylethynes. These BODIPYs have been designed to improve the electronic communication between the donor ferrocene, and the acceptor BODIPY. The photonic and electrochemical properties indicate charge transfer (CT) from the ferrocene to the BODIPY. Single crystal X-ray structures of 2', 3, and 6 show interesting supramolecular interactions. Computational studies were used to study the electronic structure of the BODIPYs.

A series of donor-acceptor ferrocenyl substituted BODIPYs have been designed and synthesized via palladium catalyzed Suzuki and Sonogashira coupling reactions. The UV-visible absorption results indicate intramolecular charge transfer from the ferrocene to the BODIPY. The fluorescence quantum yield was drastically reduced, where the ferrocenyl group was directly attached to the BODIPY. The single crystal X-ray structures of 1', 2, 3, and 4 show marvelous supramolecular interactions. The crystal structure of 1' shows an extensive hydrogen bonded 2D network, 2 shows sheet like structure, 3 shows zigzag packing along the a-axis, whereas 4 shows sheet like structure in which both the surfaces of the sheet are covered with the ferrocenyl group.