Synthesis of the Stable Ordered Conjugated Polymer Poly(dibromodiacetylene) from an Explosive Monomer

Precisely translating computed tomography diagnosis accuracy into therapeutic intervention by a carbon-iodine conjugated polymer

X-ray computed tomography (CT) has an important role in precision medicine. However, CT contrast agents with high efficiency and the ability to translate diagnostic accuracy into therapeutic intervention are scarce. Here, poly(diiododiacetylene) (PIDA), a conjugated polymer composed of only carbon and iodine atoms, is reported as an efficient CT contrast agent to bridge CT diagnostic imaging with therapeutic intervention. PIDA has a high iodine payload (>84 wt%), and the aggregation of nanofibrous PIDA can further amplify CT intensity and has improved geometrical and positional stability in vivo. Moreover, with a conjugated backbone, PIDA is in deep blue color, making it dually visible by both CT imaging and the naked eyes. The performance of PIDA in CT-guided preoperative planning and visualization-guided surgery is validated using orthotopic xenograft rat models. In addition, PIDA excels clinical fiducial markers of imaging-guided radiotherapy in efficiency and biocompatibility, and exhibits successful guidance of robotic radiotherapy on Beagles, demonstrating clinical potential to translate CT diagnosis accuracy into therapeutic intervention for precision medicine.

Crystal Structures of Lignocellulosic Furfuryl Biobased Polydiacetylenes with Hydrogen-Bond Networks: Influencing the Direction of Solid-State Polymerization through Modification of the Spacer Length

We present the topochemical polymerization of two lignocellulosic biobased diacetylenes (DAs) that only differ by an alkyl spacer length of 1 methylene (n = 1) or 3 methylene units (n = 3) between the diyne and carbamate functionalities. Their crystalline molecular organizations have the distinctive feature of being suitable for polymerization in two potential directions, either parallel or skewed to the hydrogen-bonded (HB) network. However, single-crystal structures of the final polydiacetylenes (PDAs) demonstrate that the resulting orientation of the conjugated backbones is different for these two derivatives, which lead to HB supramolecular polymer networks (2D nanosheets) for n = 1 and to independent linear PDA chains with intramolecular HBs for n = 3. Thus, spacer length modification can be considered a new strategy to influence the molecular orientation of conjugated polymer chains, which is crucial for developing the next generation of materials with optimal mechanical and optoelectronic properties. Calculations were performed on model oligodiacetylenes to evaluate the cooperativity effect of HBs in the different crystalline supramolecular packing motifs and the energy profile related to the torsion of the conjugated backbone of a PDA chain (i.e., its ability to adopt planar or helical conformations).

Halogen bonding in polymer science: towards new smart materials

The halogen bond is a special non-covalent interaction, which can represent a powerful tool in supramolecular chemistry. Although the halogen bond offers several advantages compared to the related hydrogen bond, it is currently still underrepresented in polymer science. The structural related hydrogen bonding assumes a leading position in polymer materials containing supramolecular interactions, clearly indicating the high potential of using halogen bonding for the design of polymeric materials. The current developments regarding halogen bonding containing polymers include self-assembly, photo-responsive materials, self-healing materials and others. These aspects are highlighted in the present perspective. Furthermore, a perspective on the future of this rising young research field is provided.

The incorporation of halogen bonding into polymer architectures is a new approach for the design of functional materials. This perspective emphasizes the current development in the field of halogen bonding featuring polymer materials.

Azine Steric Hindrances Switch Halogen Bonding to N-Arylation upon Interplay with σ-Hole Donating Haloarenenitriles

An interplay between 4-bromo- and 4-iodo-5-nitrophthalonitriles (XNPN, X=Br or I) and any one of the azines (pyridine 1, 4-dimethylaminopyridine 2, isoquinoline 3, 4-cyanopyridine 4, 2-methylpyridine 5, 2-aminopyridine 6, quinoline 7, 1-methylisoquinoline 8, and 2,2'-bipyridine 9) proceeds differently depending on steric and electronic effects of the heterocycles. Sterically unhindered azines 1-3 underwent N-arylation to give the corresponding azinium salts (characterized by ¹ H and ¹³ C{H} NMR and high-resolution ESI-MS). In contrast, azines 4-9 with sterically hindered N atoms or bearing an electron-withdrawing substituent, form stable co-crystals with XNPN, where two interacting molecules are bound by halogen bonding. In all obtained co-crystals, X⋅⋅⋅N structure-directed halogen bonds were recognized and theoretically evaluated including DFT calculations (PBE0-D3/def2-TZVP level of theory), QTAIM analysis, molecular electrostatic potential surfaces, and noncovalent interaction plot index. Estimated energies of halogen bonding vary from -7.6 kcal/mol (for 6 ⋅ INPN) to -11.4 kcal/mol (5 ⋅ INPN).

Topochemical polymerizations for the solid-state synthesis of organic polymers

Topochemical polymerizations are solid-state reactions driven by the alignment of monomers in the crystalline state. The molecular confinement in the monomer crystal lattice offers precise control over the tacticity, packing and crystallinity of the polymer formed in the topochemical reaction. As topochemical reactions occur under solvent- and catalyst-free conditions, giving products in high yield and selectivity/specificity that do not require tedious chromatographic purification, topochemical polymerizations are highly attractive over traditional solution-phase polymer synthesis. By this method, polymers having sophisticated structures and desired topologies can be availed. Often, such ordered packing confers attractive properties to the topochemically-synthesized polymers. Diverse categories of topochemical polymerizations are known, such as polymerizations via [2+2], [4+4], [4+2], and [3+2] cycloadditions, and polymerization of diynes, triynes, dienes, trienes, and quinodimethanes, each of which proceed under suitable stimuli like heat, light or pressure. Each class of these reactions requires a unique packing arrangement of the corresponding monomers for the smooth reaction and produces polymers with distinct properties. This review is penned with the intent of bringing all the types of topochemical polymerizations into a single platform and communicating the versatility of these lattice-controlled polymerizations. We present a brief history of the development of each category and comprehensively review the topochemical synthesis of fully-organic polymers reported in the last twenty years, particularly in crystals. We mainly focus on the various molecular designs and crystal engineering strategies adopted to align monomers in a suitable orientation for polymerization. Finally, we analyze the current challenges and future perspectives in this research field.

Vinyl Iodide Containing Polymers Directly Prepared via an Iodo-yne Polymerization

Postpolymerization modifications are a prominent route for tuning polymer properties and diversifying materials. Thus, polymers containing robust chemical handles are desirable. Vinyl iodide functionality is commonly enlisted for selective transformations on small molecules, but these chemistries, while efficient enough for postpolymerization modifications, are less frequently performed on macromolecules due to limited methods to install vinyl iodide groups into polymers. Here, we present an iodo-yne polymerization involving diynes and diiodoperfluoroalkanes to facilely give semifluorinated polymers with vinyl iodide groups throughout the polymer chain. The iodo-yne polymerization yields polymers of at least 6 kDa while open to air in aqueous solvent. We demonstrate that the iodo-yne polymers can be modified at the vinyl iodide functionality via a variety of metal-catalyzed cross-coupling reactions. Additionally, the iodide can be eliminated to give electronically activated alkynes that can undergo cycloaddition with azides. Taken together, this work will push the current boundaries of functional polymers and assist in the development of modernized, smart materials.

N,N'-Bis(pyridin-3-ylmeth-yl)ethanedi-amide monohydrate: crystal structure, Hirshfeld surface analysis and computational study

The mol-ecular structure of the title bis-pyridyl substituted di-amide hydrate, C14H14N4O2·H2O, features a central C2N2O2 residue (r.m.s. deviation = 0.0205 Å) linked at each end to 3-pyridyl rings through methyl-ene groups. The pyridyl rings lie to the same side of the plane, i.e. have a syn-periplanar relationship, and form dihedral angles of 59.71 (6) and 68.42 (6)° with the central plane. An almost orthogonal relationship between the pyridyl rings is indicated by the dihedral angle between them [87.86 (5)°]. Owing to an anti disposition between the carbonyl-O atoms in the core, two intra-molecular amide-N-H⋯O(carbon-yl) hydrogen bonds are formed, each closing an S(5) loop. Supra-molecular tapes are formed in the crystal via amide-N-H⋯O(carbon-yl) hydrogen bonds and ten-membered {⋯HNC2O}2 synthons. Two symmetry-related tapes are linked by a helical chain of hydrogen-bonded water mol-ecules via water-O-H⋯N(pyrid-yl) hydrogen bonds. The resulting aggregate is parallel to the b-axis direction. Links between these, via methyl-ene-C-H⋯O(water) and methyl-ene-C-H⋯π(pyrid-yl) inter-actions, give rise to a layer parallel to (10); the layers stack without directional inter-actions between them. The analysis of the Hirshfeld surfaces point to the importance of the specified hydrogen-bonding inter-actions, and to the significant influence of the water mol-ecule of crystallization upon the mol-ecular packing. The analysis also indicates the contribution of methyl-ene-C-H⋯O(carbon-yl) and pyridyl-C-H⋯C(carbon-yl) contacts to the stability of the inter-layer region. The calculated inter-action energies are consistent with importance of significant electrostatic attractions in the crystal.

Directional Self-Assembly and Photoinduced Polymerization of Diacetylene-Containing Platinum(II) Terpyridine Complexes

A series of newly designed and synthesized diacetylene-containing platinum(II) terpyridine complexes exhibited intriguing self-assembly properties. Facilitated by Pt⋅⋅⋅Pt, π-π stacking, hydrogen-bonding and hydrophobic-hydrophobic interactions, these complexes are preorganized to readily undergo topochemical polymerization reactions upon photoirradiation. The in situ polymerization of the diacetylene units to form polydiacetylene, indicated by the UV/Vis spectral changes, gel permeation chromatography and dynamic light scattering, was found to alter their assembly behaviours, as revealed by TEM images.

Halogen-bonded cocrystals ofN-salicylidene Schiff bases and iodoperfluorinated benzenes: hydroxyl oxygen as a halogen bond acceptor

Novel halogen bondedo-hydroxy imine cocrystals with 1,3,5-triiodotrifluoro-benzene and 1,2-, 1,3- and 1,4-diiodotetrafluorobenzene have been synthesized.

Isomorphous crystal structures of chlorodi-acetyl-ene and iododi-acetyl-ene derivatives: simultaneous hydrogen and halogen bonds on carbon-yl

The crystal structures of tert-butyl (5-chloro-penta-2,4-diyn-1-yl)carbamate, C10H12ClNO2 (II), and tert-butyl (5-iodo-penta-2,4-diyn-1-yl)carbamate, C10H12INO2 (IV), are isomorphous to previously reported structures and accordingly their mol-ecular and supra-molecular structures are similar. In the crystals of (II) and (IV), mol-ecules are linked into very similar two-dimensional wall organizations with anti-parallel carbamate groups involved in a combination of hydrogen and halogen bonds (bifurcated N-H⋯O=C and C≡C-X⋯O=C inter-actions on the same carbonyl group). There is no long-range parallel stacking of diynes, so the topochemical polymerization of di-acetyl-ene is prevented. A Cambridge Structural Database search revealed that C≡C-X⋯O=C contacts shorter than the sum of the van der Waals radii are scarce (only one structure for the C≡C-Cl⋯O=C inter-action and 13 structures for the similar C≡C-I⋯O=C inter-action).

Crystal-to-Crystal Synthesis of Triazole-Linked Pseudo-proteins via Topochemical Azide-Alkyne Cycloaddition Reaction

Isosteric replacement of amide bond(s) of peptides with surrogate groups is an important strategy for the synthesis of peptidomimetics (pseudo-peptides). Triazole is a well-recognized bio-isostere for peptide bonds, and peptides with one or more triazole units are of great interest for different applications. We have used a catalyst-free and solvent-free method, viz., topochemical azide-alkyne cycloaddition (TAAC) reaction, to synthesize pseudo-proteins with repeating sequences. A designed β-sheet-forming l-Ala-l-Val dipeptide containing azide and alkyne at its termini (N₃-Ala-Val-NHCH₂C≡CH, 1) was synthesized. Single-crystal XRD analysis of the dipeptide 1 showed parallel β-sheet arrangement along the b-direction and head-to-tail arrangement of such β-sheets along the c-direction. This head-to-tail arrangement along the c-direction places the complementary reacting motifs, viz., azide and alkyne, of adjacent molecules in proximity. The crystals of dipeptide 1, upon heating at 85 °C, underwent crystal-to-crystal polymerization, giving 1,4-triazole-linked pseudo-proteins. This TAAC polymerization was investigated by various time-dependent techniques, such as NMR, IR, DSC, and PXRD. The crystal-to-crystal nature of this transformation was revealed from polarizing microscopy and PXRD experiments, and the regiospecificity of triazole formation was evidenced from various NMR techniques. The MALDI-TOF spectrum showed the presence of pseudo-proteins >7 kDa.

Neutral iodotriazoles as scaffolds for stable halogen-bonded assemblies in solution

The halogen bond (XB) donor properties of neutral 1,4-diaryl-5-iodo-1,2,3-triazoles are explored using a combination of computational and experimental results and are shown to be competitive in halogen bonding efficiency with the classic pentafluoroiodobenzene XB donor. The SNAr reactivity of these donors permits the facile assembly of an iodotriazole functionalised with a 3-oxypyridine XB acceptor, thus generating a molecular scaffold capable of undergoing dimerisation through the formation of two halogen bonds. The formation of this halogen-bonded dimer is demonstrated by 1H and DOSY NMR experiments and a plausible structure generated using DFT calculations.

Hydrochromic Approaches to Mapping Human Sweat Pores

Hydrochromic materials, which undergo changes in their light absorption and/or emission properties in response to water, have been extensively investigated as humidity sensors. Recent advances in the design of these materials have led to novel applications, including monitoring the water content of organic solvents, water-jet-based rewritable printing on paper, and hydrochromic mapping of human sweat pores. Our interest in this area has focused on the design of hydrochromic materials for human sweat pore mapping. We recognized that materials appropriate for this purpose must have balanced sensitivities to water. Specifically, while they should not undergo light absorption and/or emission transitions under ambient moisture conditions, the materials must have sufficiently high hydrochromic sensitivities that they display responses to water secreted from human sweat pores. In this Account, we describe investigations that we have carried out to develop hydrochromic substances that are suitable for human sweat pore mapping. Polydiacetylenes (PDAs) have been extensively investigated as sensor matrices because of their stimulus-responsive color change property. We found that incorporation of headgroups composed of hygroscopic ions such as cesium or rubidium and carboxylate counterions enables PDAs to undergo a blue-to-red colorimetric transition as well as a fluorescence turn-on response to water. Very intriguingly, the small quantities of water secreted from human sweat pores were found to be sufficient to trigger fluorescence turn-on responses of the hydrochromic PDAs, allowing precise mapping of human sweat pores. Since the hygroscopic ion-containing PDAs developed in the initial stage display a colorimetric transition under ambient conditions that exist during humid summer periods, a new system was designed. A PDA containing an imidazolium ion was found to be stable under all ambient conditions and showed temperature-dependent hydrochromism corresponding to a colorimetric change near body temperature. This feature enables the use of this technique to generate high-quality images of sweat pores. This Account also focuses on the results of the most recent phase of this investigation, which led to the development of a simple yet efficient and reliable technique for sweat pore mapping. The method utilizes a hydrophilic polymer composite film containing fluorescein, a commercially available dye that undergoes a fluorometric response as a result of water-dependent interconversion between its ring-closed spirolactone (nonfluorescent) and ring-opened fluorone (fluorescent) forms. Surface-modified carbon nanodots (CDs) have also been found to be efficient for hydrochromic mapping of human sweat pores. The results discovered by Lou et al. [ Adv. Mater. 2015 , 27 , 1389 ] are also included in this Account. Sweat pore maps obtained from fingertips using these materials were found to be useful for fingerprint analysis. In addition, this hydrochromism-based approach is sufficiently sensitive to enable differentiation between sweat-secreting active pores and inactive pores. As a result, the techniques can be applied to clinical diagnosis of malfunctioning sweat pores. The directions that future research in this area will follow are also discussed.

Directing the Crystallization of Dehydro[24]annulenes into Supramolecular Nanotubular Scaffolds

The self-assembly of a series of dehydro[24]annulene derivatives into columnar stacks has been examined for its latent ability to form π-conjugated carbon-rich nanotubular structures through topochemical polymerizations. We have studied the parameters affecting self-assembly, including the nature of the substituent and crystallization conditions, using 10 different dehydro[24]annulene derivatives. In particular, hydrogen-bonding interactions through carbamate groups were found to be especially useful at directing the formation of nanotubular supramolecular assemblies. We have also evaluated the electronic coupling between neighboring dehydroannulene molecules within these supramolecular assemblies. Density functional calculations on the stacked supramolecular nanotube assemblies show that transfer integrals vary considerably between the three columnar assemblies, ranging from moderate to high (59-98 meV for the highest occupied molecular orbitals, 63-97 meV for the lowest unoccupied molecular orbitals), depending on the local molecular topology. In addition, the dehydro[24]annulene derivatives afforded distinct architectures in the crystal, including nanochannel arrays, sheets with solvent-filled pores, and lamellae. This work is an essential step toward a controlled formation of covalently linked carbon-rich nanostructures generated from molecular precursors with a latent diacetylene reactivity.

A Magnetically Responsive Polydiacetylene Precursor for Latent Fingerprint Analysis

A magnetically responsive diacetylene (DA) powder was developed for the visualization of latent fingerprints. A mixture of the DA and magnetite nanoparticles, applied to a surface containing latent fingermarks, becomes immobilized along the ridge patterns of the fingerprints when a magnetic field is applied. Alignment along the ridge structures is a consequence of favorable hydrophobic interactions occurring between the long alkyl chains in the DAs and the lipid-rich, sebaceous latent fingermarks. UV irradiation of the DA-magnetite composite immobilized on the latent fingerprint results in the generation of blue-colored PDAs. Heat treatment of the blue-colored image promotes a blue-to-red transition as well as fluorescence turn-on. A combination of the aligned pale brown-colored monomeric state, UV irradiation generated blue-colored PDA state, as well as the heat treatment generated red-colored and fluorescent PDA state enables efficient visual imaging of a latent fingerprint, which is deposited on various colored solid surfaces.