8 research outputs found
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<sup>II</sup> to Cu<sup>I</sup> ions during the reaction and their unique geometrical preferences
lead to linking of the octahedral Cu<sup>II</sup> complexes by tetrahedral
Cu<sup>I</sup> 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<sup>II</sup> to Cu<sup>I</sup> ions during the reaction and their unique geometrical preferences
lead to linking of the octahedral Cu<sup>II</sup> complexes by tetrahedral
Cu<sup>I</sup> 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><sub><b>4</b></sub><b>L</b> functionalized with
1,2,3-triazole was rationally designed and synthesized to access nitrogen-rich
MOFs for selective adsorption of CO<sub>2</sub>. The cadmium MOF,
that is, <b>Cd-L</b>, obtained by the reaction of <b>H</b><sub><b>4</b></sub><b>L</b> with CdÂ(NO<sub>3</sub>)<sub>2</sub>, 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 CO<sub>2</sub> 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′-tetraÂkisÂ(4-(α-carboxy)ÂmethÂoxyÂphenyl)-2,2′,6,6′-tetraÂmethoxy-1,1′-biphenyl
(<b>H</b><sub><b>4</b></sub><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><sub><b>4</b></sub><b>L</b> were
surmised to twist the aromatic planes and impart porosity to the resultant
MOFs, the (α-carÂboxy)ÂmethÂoxyÂphenyl moieties
at the periphery were envisaged to enable requisite flexibility for
metal–ligand coordination polymerization. The reactions of <b>H</b><sub><b>4</b></sub><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><sub><b>4</b></sub><b>L</b> with
ZnI<sub>2</sub> 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><sub><b>4</b></sub><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 CO<sub>2</sub> Capture
A fluorescent
organic linker, namely, 10,10′-bisÂ(4-carboxyphenyl)-9,9′-bianthryl
(<b>H</b><sub><b>2</b></sub><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><sub><b>2</b></sub><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<sup>–</sup> ions. Notably, the reaction
of <b>H</b><sub><b>2</b></sub><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 CO<sub>2</sub> 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><sub>d</sub> and <i>T</i><sub>g</sub>, 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/m<sup>2</sup> 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