Coordination Polymerization of 5,5′-Dinitro‑2<i>H</i>,2<i>H</i>′‑3,3′-bi-1,2,4-triazole Leads to a Dense Explosive with High Thermal Stability

High-energy coordination polymers (CPs) based on nitrogen-rich ligands are an emerging class of explosives. However, modulation of the energetic properties of high-energy CPs and the establishment of their structure–function relationship remain in their infancy. In the present study, the utility of coordination polymerization as a technique to modulate the application of critical energetic properties, such as density and thermal stability, of a secondary explosive, 5,5′-dinitro-2<i>H</i>,2<i>H</i>′-3,3′-bi-1,2,4-triazole (DNBT), is presented. <b>Ni-DNBT</b> is a discrete octahedral complex with density lower than that of DNBT. <b>Cu-DNBT</b> also contains octahedral metal coordination, similar to that in <b>Ni-DNBT</b>, as the building unit; however, the partial reduction of Cu^II to Cu^I ions during the reaction and their unique geometrical preferences lead to linking of the octahedral Cu^II complexes by tetrahedral Cu^I ions and render the resultant material a one-dimensional polymer with high density. In fact, <b>Cu-DNBT</b> has the highest density among all of the DNBT-based energetics. Furthermore, <b>Cu-DNBT</b> exhibits thermal stability superior to that of both <b>Ni-DNBT</b> and DNBT. <b>Cu-DNBT</b> is one of the two DNBT-based energetic materials and one of the few energetics that are stable at temperatures higher than 300 °C

Coordination Polymerization of 5,5′-Dinitro‑2<i>H</i>,2<i>H</i>′‑3,3′-bi-1,2,4-triazole Leads to a Dense Explosive with High Thermal Stability

High-energy coordination polymers (CPs) based on nitrogen-rich ligands are an emerging class of explosives. However, modulation of the energetic properties of high-energy CPs and the establishment of their structure–function relationship remain in their infancy. In the present study, the utility of coordination polymerization as a technique to modulate the application of critical energetic properties, such as density and thermal stability, of a secondary explosive, 5,5′-dinitro-2<i>H</i>,2<i>H</i>′-3,3′-bi-1,2,4-triazole (DNBT), is presented. <b>Ni-DNBT</b> is a discrete octahedral complex with density lower than that of DNBT. <b>Cu-DNBT</b> also contains octahedral metal coordination, similar to that in <b>Ni-DNBT</b>, as the building unit; however, the partial reduction of Cu^II to Cu^I ions during the reaction and their unique geometrical preferences lead to linking of the octahedral Cu^II complexes by tetrahedral Cu^I ions and render the resultant material a one-dimensional polymer with high density. In fact, <b>Cu-DNBT</b> has the highest density among all of the DNBT-based energetics. Furthermore, <b>Cu-DNBT</b> exhibits thermal stability superior to that of both <b>Ni-DNBT</b> and DNBT. <b>Cu-DNBT</b> is one of the two DNBT-based energetic materials and one of the few energetics that are stable at temperatures higher than 300 °C

Carbon Dioxide Capture by a Metal–Organic Framework with Nitrogen-Rich Channels Based on Rationally Designed Triazole-Functionalized Tetraacid Organic Linker

A semirigid tetraacid linker <b>H</b>_<b>4</b><b>L</b> functionalized with 1,2,3-triazole was rationally designed and synthesized to access nitrogen-rich MOFs for selective adsorption of CO₂. The cadmium MOF, that is, <b>Cd-L</b>, obtained by the reaction of <b>H</b>_<b>4</b><b>L</b> with Cd­(NO₃)₂, is found to be a 3D porous framework structure that is robust to desolvation. Crystal structure analysis reveals channels that are decorated by the triazole moieties of <b>L</b>. Gas adsorption studies show that <b>Cd-L</b> MOF permits remarkable CO₂ uptake to the extent of 99 and 1000 cc/g at 1 and 30 bar, respectively, at 0 °C. While literature survey reveals that <b>MIL-112</b>, constructed from a 1,2,3-triazole functionalized linker, exhibits no porosity to gas adsorption due to structural flexibility, the results with <b>Cd-L</b> MOF described herein emphasize how rigidification of the organic linker improves gas uptake properties of the resultant MOF

Metal-Mediated Self-Assembly of a <i>Twisted</i> Biphenyl-Tetraacid Linker with Semi-rigid Core and Peripheral Flexibility: Concomitant Formation of Compositionally Distinct MOFs

A semi-rigid organic linker, namely, 3,3′,5,5′-tetra­kis­(4-(α-carboxy)­meth­oxy­phenyl)-2,2′,6,6′-tetra­methoxy-1,1′-biphenyl (<b>H</b>_<b>4</b><b>L</b>), was designed and synthesized to access metal–organic frameworks (MOFs). While the <i>ortho</i>-methoxy substituents in the biphenyl core of <b>H</b>_<b>4</b><b>L</b> were surmised to twist the aromatic planes and impart porosity to the resultant MOFs, the (α-car­boxy)­meth­oxy­phenyl moieties at the periphery were envisaged to enable requisite flexibility for metal–ligand coordination polymerization. The reactions of <b>H</b>_<b>4</b><b>L</b> with Cd, Mn, and Zn salts indeed yielded MOFs, i.e., <b>Cd-L</b>, <b>Mn-L</b>, <b>Zn-Lsqc</b>, and <b>Zn-Ldia</b>, with interesting structural features and unusual inorganic SBUs. In particular, the reaction of <b>H</b>_<b>4</b><b>L</b> with ZnI₂ in DMF at 90 °C over 2 days led to concomitant formation of a pair of <i>compositionally distinct</i> Zn-MOFs, i.e., <b>Zn-Ldia</b> and <b>Zn-Lsqc</b>, each of which could be accessed exclusively by controlling the reaction conditions. The diversity observed in the structures of MOFs formed with the linker <b>H</b>_<b>4</b><b>L</b> with a limited number of metal ions sufficiently emphasizes the importance of the attributes of the linker in the formation of 3D MOFs; the latter are desirable from the stability and exfoliation points of view when the MOFs are explored for applications such as gas storage, catalysis, etc. In corroboration of our previous results, it emerges that the flexibility that is built into the structure of the organic linker, both at the central core and at the periphery, leads to concomitant formation of compositionally distinct MOFs in addition to diverse SBUs and disparate framework topologies

Metal Effects on the Sensitivity of Isostructural Metal–Organic Frameworks Based on 5‑Amino-3-nitro‑1<i>H</i>‑1,2,4-triazole

Two energetic metal–organic frameworks (MOFs), Co-ANTA and Zn-ANTA, are synthesized from 5-amino-3-nitro-1<i>H</i>-1,2,4-triazole (ANTA) and exhibit superior oxygen balance, density, and thermal stability compared to ANTA. The superior oxygen balance is achieved through a combination of hydroxide ligands and deprotonated linkers. Although the materials are isostructural and have similar density, oxygen balance, and sensitivity to heat, their impact sensitivities are significantly different. Similar to ANTA, Zn-ANTA is fairly insensitive to impact. By contrast, the impact sensitivity of ANTA is increased significantly after coordination polymerization with cobalt. The disparate impact sensitivities of the compounds might be attributed to the different electronic configurations of the metal ions constituting the frameworks

Diverse Metal–Organic Materials (MOMs) Based on 9,9′-Bianthryl-Dicarboxylic Acid Linker: Luminescence Properties and CO₂ Capture

A fluorescent organic linker, namely, 10,10′-bis­(4-carboxyphenyl)-9,9′-bianthryl (<b>H</b>_<b>2</b><b>L</b>), was rationally designed and synthesized to access luminescent metal–organic materials (MOMs). A series of structurally diverse MOMs was synthesized with the diacid linker <b>H</b>_<b>2</b><b>L</b> by reacting it with main group, transition, and lanthanide metal ions under different conditions. Among them, <b>Zn-L</b> MOM is a 1D polymeric chain, while <b>Cd-L</b> is a 2D structure in which 4,4′-bipyridyls mediate the formation of 2D networks by linking up the 1D metal–carboxylate chains. The <b>Pb-L</b> MOM is found to be a 2D polymeric net, while <b>Sr-L</b>, obtained under similar reaction conditions, is a noninterpenetrated 3D polymeric structure; the extension from 2D to 3D framework occurs by mediation of Cl^– ions. Notably, the reaction of <b>H</b>_<b>2</b><b>L</b> with the lanthanide ions yielded isostructural 3D MOFs, i.e., <b>Tb-L</b>, <b>Eu-L</b>, <b>Sm-L</b>, <b>Nd-L</b>, <b>La-L</b>, <b>Pr-L</b>, <b>Gd-L</b>, and <b>Yb-L</b>, which are noninterpenetrated and porous. The Ln-MOFs are highly robust and stable to solvent exclusion. The representative Ln-MOFS, viz., <b>Tb-L</b>, <b>Eu-L</b>, and <b>Sm-L</b>, are shown to exhibit gas adsorption at ambient temperatures; the CO₂ uptake capacities are found to be in the range of the highest values observed for Ln-MOFs to date. All the MOMs, including lanthanide MOFs, exhibit linker-based luminescence in the solid state

Benzophenones as Generic Host Materials for Phosphorescent Organic Light-Emitting Diodes

Despite the fact that benzophenone has traditionally served as a prototype molecular system for establishing triplet state chemistry, materials based on molecular systems containing the benzophenone moiety as an integral part have not been exploited as generic host materials in phosphorescent organic light-emitting diodes (PhOLEDs). We have designed and synthesized three novel host materials, i.e., BP2–BP4, which contain benzophenone as the active triplet sensitizing molecular component. It is shown that their high band gap (3.91–3.93 eV) as well as triplet energies (2.95–2.97 eV) permit their applicability as universal host materials for blue, green, yellow, and red phosphors. While they serve reasonably well for all types of dopants, excellent performance characteristics observed for yellow and green devices are indeed the hallmark of benzophenone-based host materials. For example, maximum external quantum efficiencies of the order of 19.2% and 17.0% were obtained from the devices fabricated with yellow and green phosphors using BP2 as the host material. White light emission, albeit with rather poor efficiencies, has been demonstrated as a proof-of-concept by fabrication of co-doped and stacked devices with blue and yellow phosphors using BP2 as the host material

Nitrogen-Free Bifunctional Bianthryl Leads to Stable White-Light Emission in Bilayer and Multilayer OLED Devices

White organic light-emitting diodes (WOLEDs) are at the center stage of OLED research today because of their advantages in replacing the high energy-consuming lighting technologies in vogue for a long time. New materials that emit white light in simple devices are much sought after. We have developed two novel electroluminescent materials, referred to as <b>BABZF</b> and <b>BATOMe</b>, based on a twisted bianthryl core, which are brilliantly fluorescent, thermally highly stable with high <i>T</i>_d and <i>T</i>_g, and exhibit reversible redox property. Although inherently blue emissive, <b>BABZF</b> leads to white-light emission (CIE ≈ 0.28, 0.33) with a moderate power efficiency of 2.24 lm/W and a very high luminance of 15 600 cd/m² in the fabricated multilayer nondoped OLED device. This device exhibited excellent color stability over a range of applied potential. Remarkably, similar white-light emission was captured even from a double-layer device, attesting to the innate hole-transporting ability of <b>BABZF</b> despite it being non-nitrogenous, that is, lacking any traditional hole-transporting di-/triarylamino group(s). Similar studies with <b>BATOMe</b> led to inferior device performance results, thereby underscoring the importance of dibenzofuryl groups in <b>BABZF</b>. Experimental as well as theoretical studies suggest the possibility of emission from multiple species involving <b>BABZF</b> and its exciplex and electroplex in the devices. The serendipitously observed white-light emission from a double-layer device fabricated with an unconventional hole-transporting material (HTM) opens up new avenues to create new non-nitrogenous HTMs that may lead to more efficient white-light emission in simple double-layer devices