Manipulating the cavity of a porous material changes the photoreactivity of included guests

Dewal, Mahender B.; Xu, Yuewen; Yang, Jun; Mohammed, F.; Smith, Mark D.; Shimizu, Linda S.

doi:10.1039/b805895d

Cited by 36 publications

(60 citation statements)

References 24 publications

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“…[27][28][29] Our previous research has concentrated on adjusting the size and shape of the rigid macrocycles using different building blocks such as m-xylene, phenyl ether, or benzophenone. In this paper, we explored the † University of South Carolina.…”

Section: Introductionmentioning

confidence: 99%

Macrocycles with Switchable exo/endo Metal Binding Sites

et al. 2009

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We report herein the synthesis and metal complexation properties of two macrocyclic hosts that contain two 2,2'-bipyridines and two urea groups. These hosts take advantage of the conformationally mobile 5,5'-positions of the bipyridines to give metal binding sites that are dynamic. By simple bond rotation, these hosts can exchange an interior (endo) situated metal binding site for an exterior (exo) binding site. We examine the solid-state structures of the two free hosts and two coordination complexes ([Cd(host 1)(H(2)O)(NO(3))(2)] and [Ag(2)(host 2)](SO(3)CF(3))(2)) using X-ray crystallography. Analysis of these crystal structures suggests that the bipyridine groups within the hosts are able to rotate to access multiple conformations including the desired exo and endo conformations. We also investigate the binding affinity of these new ligands in solution by UV-vis titrations with a series of metal nitrate salts (Ag, Cd, Zn, Ni, Mn, Fe, Co, Cr, and Cu) to afford discrete metal complexes. Some complexes showed a slow subsequent assembly to yield coordination polymers. Thus, these systems may afford unique insights into the process of metal organic framework formation.

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Section: Introductionmentioning

confidence: 99%

Macrocycles with Switchable exo/endo Metal Binding Sites

et al. 2009

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“…Photodimerization of the above enones could not happen within 33c-tube. Instead, the nanotube was able to act as a triplet sensitizer for the cis-trans photoisomerization of trans-β-methylstyrene and selective oxidation of 2-methyl-2-butene to a primary allylic alcohol (Scheme 3.14) [70,109]. As well, an enlarged nanotube 33d-tube was shown to facilitate the selective photodimerization of coumarin to the anti-head-to-head product [71].…”

Section: Auxiliary Templatesmentioning

confidence: 96%

Hydrogen Bonding in Supramolecular Crystal Engineering

Wang

Zheng

2015

Lecture Notes in Chemistry

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This chapter emphases the important role of hydrogen bonding in crystal engineering for preparing fascinating architectures and engineering desired properties. The relatively high directionality and strength of hydrogen bonds make the prediction and control of molecular orientation in organic solids practical and reliable. Especially, strong hydrogen bonds like O-H···O, O-H···N, and N-H···O interactions are more useful. The introduction of supramolecular synthons and retrosynthesis theory has helped crystal chemists a lot in understanding and designing more complex structures. A large number of crystal structures reported in Cambridge Structure Database (CSD) provided a helpful tool for searching and analyzing specific interaction modes. Up to now, with the development of basic concepts and principles and the wide applications, the subject of crystal engineering has matured. Various intriguing structures and complicated entanglements have been constructed based on hydrogen bonds, such as nanocapsules, nanotubes, and n-Borromean arrayed topologies. The crystal engineering strategy has lent chemists the ability to control solid state reactions regio-and stereo-specifically and improve the physicochemical properties of drugs using pharmaceutical cocrystals. In addition, it will be seen that hydrogen bonding can also be used to prepare robust porous materials for gas adsorption and separation.

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“…The photogenerated radical was first noted when investigating the applications of benzophenone bis -urea macrocycle 1 to facilitate selective photooxidations. 6, 7 The prolonged stability of these endogenous radicals at room temperature appears to be a consequence of the columnar assembly and crystal packing of the porous organic crystals, where as no evidence of radical formation is observed in solution. 6 Herein, we probe the structure of the radical, estimate its quantity, and evaluate its lifetime by EPR spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

“…Upon recrystallization from hot DMSO, 1 assembles in needle-like crystals through predictable bifurcated urea hydrogen-bonding interactions to afford columns (Figure 1). 7 The crystals are robust and contain accessible channels that are filled with DMSO guests (Figure 3b). DMSO guests can be removed by heating and other solvents and substrates can be readily loaded in the channels.…”

Section: Introductionmentioning

confidence: 99%

“…DMSO guests can be removed by heating and other solvents and substrates can be readily loaded in the channels. 7 The assembled structure enforces close contacts between the benzophenone groups to the methylene H’s on neighbouring columns (2.44 – 2.81 Å, Figure S4) and orients individual benzophenone units close in space. 6 Molecular self-assembly and crystal packing in 1 dramatically quenches the phosphorescence lifetime from µs to < 1 ns, likely through a non-radiative pathway.…”

Section: Introductionmentioning

confidence: 99%

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Persistent Radicals of Self‐assembled Benzophenone bis‐Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid‐state DNP MAS Spectroscopy

DeHaven

Tokarski

Korous

et al. 2017

Chemistry A European J

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UV-irradiation of a self-assembled benzophenone bis-urea macrocycle generates µM amounts of radicals that persist for weeks under ambient conditions. High-Field EPR and variable temperature X-band EPR studies suggest a resonance stabilized radical pair through H-abstraction. These endogenous radicals were applied as a polarizing agent for magic angle spinning (MAS) dynamic nuclear polarization (DNP) NMR enhancement. The field-stepped DNP enhancement profile exhibits a sharp peak with a maximum enhancement of εon/off = 4 superimposed on a nearly constant DNP enhancement of εon/off = 2 over a broad field range. This maximum coincides with the high field EPR absorption spectrum, consistent with an Overhauser effect mechanism. DNP enhancement was observed for both the host and guests, suggesting that even low levels of endogenous radicals can facilitate the study of host-guest relationships in the solid-state.

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Manipulating the cavity of a porous material changes the photoreactivity of included guests

Cited by 36 publications

References 24 publications

Macrocycles with Switchable exo/endo Metal Binding Sites

Macrocycles with Switchable exo/endo Metal Binding Sites

Hydrogen Bonding in Supramolecular Crystal Engineering

Persistent Radicals of Self‐assembled Benzophenone bis‐Urea Macrocycles: Characterization and Application as a Polarizing Agent for Solid‐state DNP MAS Spectroscopy

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