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ABSTRACT: In this report, we have investigated the correlations between structure and light-induced electron transfer of one known and three new axially coordinated cobaloxime-based supramolecular photocatalysts for the reduction of protons to hydrogen. Solution-phase X-ray scattering and ultrafast transient optical spectroscopy analyses were used in tandem to correlate the self-assembled photocatalysts' structural integrity in solution with electron transfer and charge separation between the photosensitizer and catalyst fragments. Biphasic excited state decay kinetics were observed for several of the assemblies, suggesting that configurational dispersion plays a role in limiting photoinduced electron transfer. Notably, an assembly featuring a "push-pull" donor-photosensitizer-acceptor triad motif exhibits considerable ultrafast excited state quenching and, of the assemblies examined, presents the strongest opportunity for efficient solar energy conversion. These results will assist in the design and development of next-generation supramolecular photocatalyst architectures.
The Journal of Physical Chemistry B 11/2010; 114(45):14572-81. · 3.70 Impact Factor
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ABSTRACT: A new, twofold interpenetrated metal-organic framework (MOF) material has been synthesized that demonstrates dramatic steps in the adsorption and hysteresis in the desorption of CO(2). Measurement of the structure by powder X-ray diffraction (PXRD) and pair distribution function (PDF) analysis indicates that structural changes upon CO(2) sorption most likely involve the interpenetrated frameworks moving with respect to each other.
Chemistry 11/2009; 16(1):276-81. · 5.93 Impact Factor
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ABSTRACT: A Zn-based, mixed-ligand (pillared paddlewheel), metal-organic framework (MOF) has been covalently and quantitatively decorated with free carboxylic acids to demonstrate the utility of covalent post-synthesis modification in the construction of otherwise inaccessible carboxy-functionalized MOFs.
Chemical Communications 08/2009; · 6.17 Impact Factor
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Small 05/2009; 5(15):1727-31. · 8.35 Impact Factor
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ABSTRACT: A new noncatenated metal-organic framework containing pendant alcohol functionalities was synthesized. The alcohols were then post-synthetically converted to either lithium or magnesium alkoxides, with the incorporated metals anchored far from nodes or carboxylate functionalities. The metal alkoxide sites can be obtained stoichiometrically while maintaining the permanent porosity and large surface area of the parent hydroxylated material. The incorporated metal ions are found to induce an unusual pattern of binding energetics for H(2): isosteric heats of adsorption increase, rather than decrease, with increasing H(2) loading. Additionally, at 1 atm and 77 K, uptake (at least with low Li(+) loading) is increased by two hydrogen molecules per Li(+).
Journal of the American Chemical Society 04/2009; 131(11):3866-8. · 9.91 Impact Factor
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ABSTRACT: Careful processing of four representative metal-organic framework (MOF) materials with liquid and supercritical carbon dioxide (ScD) leads to substantial, or in some cases spectacular (up to 1200%), increases in gas-accessible surface area. Maximization of surface area is key to the optimization of MOFs for many potential applications. Preliminary evidence points to inhibition of mesopore collapse, and therefore micropore accessibility, as the basis for the extraordinarily efficacious outcome of ScD-based activation.
Journal of the American Chemical Society 01/2009; 131(2):458-60. · 9.91 Impact Factor
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ABSTRACT: The occluded solvent in a mixed ligand metal-organic framework has been displaced by n-hexanol, chloroform, and nitrobenzene in a crystal to crystal guest exchange. The X-ray structures of the three new solvent adducts of Zn 2 NDC 2 DPNI 2 reveal the complete replacement of N 0 ,N-dimethylformamide with the new guest. Structural changes to the framework geometry in response to the size of the incoming guest are also exhibited. These new frameworks are characterized by powder X-ray diffraction, thermal gravimetric analysis coupled with infrared spectroscopy, and cross-polarization magic angle spinning NMR.
01/2009; 9:4588-4591.
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ABSTRACT: A permanently microporous metal-organic framework compound with the formula Zn(2)(NDC)(2)(diPyTz) (NDC = 2,6-naphthalenedicarboxylate, diPyTz = di-3,6-(4-pyridyl)-1,2,4,5-tetrazine) has been synthesized. The compound, which features a triply catenating, pillared-paddlewheel structure, was designed to be easily chemically reduced (diPyTz sites) by appropriate channel permeants. Reduction was achieved by using the naphthalenide anion, with the accompanying metal cation (Li(+), Na(+) or K(+)) serving to dope the compound in extraframework fashion. H(2) uptake at 1 atm and 77 K increases from 1.12 wt % for the neutral material to 1.45, 1.60, and 1.51 wt % for the Li(+)-, Na(+)-, and K(+)-doped materials, respectively. The isosteric heats of adsorption are similar for all four versions of the material despite the large uptake enhancements for the reduced versions. Nitrogen isotherms were also measured in order to provide insight into the mechanisms of uptake enhancement. The primary mechanism is believed to be dopant-facilitated displacement of catenated frameworks by sorbed H(2). More extensive cation doping decreases the H(2) loading.
Langmuir 01/2009; 25(1):503-8. · 4.19 Impact Factor
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ABSTRACT: Using a steric self-sorting strategy, the assembly of highly ordered and rigid supramolecular boxes possessing catalytic properties has been achieved in one step. The formation of these assemblies, comprising up to 18 porphyrin centers, was readily confirmed by solution X-ray scattering in conjunction with fluorescent spectroscopy. Size-selective and enantioselective oxidation catalysis were both demonstrated.
Journal of the American Chemical Society 12/2008; 130(50):16828-9. · 9.91 Impact Factor
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Journal of the American Chemical Society 08/2008; 130(27):8598-9. · 9.91 Impact Factor
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ABSTRACT: Combining linear Zn porphyrin trimers with orthogonally derivatized porphyrin dimers leads rapidly and spontaneously to the formation of monodisperse, torsionally constrained boxes comprising six components and a total of 16 metalloporphyrins. In situ X-ray scattering measurements confirm the formation of monodisperse assemblies of precisely the size expected from model box structures. While simple subunits yield highly symmetrical boxes, we find that sterically demanding subunits produce unusual twisted boxes. Previous studies of porphyrin-based box-like assemblies (squares) for selective catalysis and molecular sieving revealed two function-inhibiting structural problems: torsional motion along the metal-porphyrin-metal axis and ambiguous outside versus inside functionalization (via axial ligation of available Zn(II) sites). The new 16-porphyrin box assemblies eliminate both problems.
Journal of the American Chemical Society 02/2008; 130(3):836-8. · 9.91 Impact Factor
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Journal of the American Chemical Society 11/2007; 129(42):12680-1. · 9.91 Impact Factor
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Journal of the American Chemical Society 09/2007; 129(31):9604-5. · 9.91 Impact Factor
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ABSTRACT: Supramolecular porphyrin prisms have been obtained via coordinative self-assembly and characterized by 1H NMR, PFG NMR, electronic absorption spectroscopy and synchrotron-based measurements of solution phase X-ray scattering and diffraction.
Chemical Communications 12/2006; · 6.17 Impact Factor
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ABSTRACT: The reaction of Zn(NO3)2 x 6H2O, various dicarboxylic acids, and either 4,4'-bipyridine or N,N'-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxydiimide produces a family of anisotropic, mixed-ligand, open-framework compounds featuring paddle-wheel-type coordination of Zn(II) pairs in two dimensions and pyridyl ligand pillaring in the third. Despite 2-fold interpenetration, the compounds contain channels of molecular dimensions and several are permanently microporous, displaying high internal surface areas.
Inorganic Chemistry 08/2005; 44(14):4912-4. · 4.60 Impact Factor
