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Rhett C Smith

Publications and source records attributed to Rhett C Smith.

10 recordsLinked to original sources
PubMed2006

Conjugated metallopolymers for fluorescent turn-on detection of nitric oxide.

A series of eight pi-conjugated polymers (CPs) composed of phenylenevinylene, phenyleneethynylene, fluorene, and thiophene derivatives have been prepared with bipyridyl or terpyridyl substituents within the pi-conjugated backbone or at side-chain positions. These ligand-modified CPs serve as macromolecular scaffolds for conducting metallopolymers. The optical and photoluminescent properties of the polymers and corresponding copper(II) metallopolymers were investigated. Copper(II) is a highly efficient quencher of CP emission (75-100% quenching). CPs featuring bipyridyl units within the CP backbone are quenched more efficiently than those with terpyridyl units. The copper(II) metallopolymer undergoes reduction to the corresponding copper(I) species upon reaction with nitric oxide, with concomitant changes in integrated emission ranging from a 50% decrease to a 320% increase. The positive emission response is largest when Cu(II) was bound to the CP through bipyridyl units within the backbone, making these materials the best candidates for NO sensing by a turn-on emission mechanism.

Copper↗
PubMed2006

Luminescent properties of water-soluble conjugated metallopolymers and their application to fluorescent nitric oxide detection.

Water-soluble pi-conjugated polymers (CPs) incorporating 5,5'-(2,2'-dipyridyl) (CP1) or 6,6'-(2,2'-dipyridyl) (CP2) units within the pi-conjugated backbone were prepared as scaffolds for macromolecular metal complexation. The response of CP emission to a range of metal ions was investigated in water, 10 mM aqueous sodium dodecyl sulfate, and acetonitrile/water (95:5). Cupric ions are the most efficient quenchers of CP emission, with K(SV) = 1.1 x 10(5) and 5.2 x 10(4) M(-1) in water for CP1a (40% bipyridyl monomer units) and CP1b (20% bipyridyl monomer units), respectively. Quenching is approximately twice as effective in acetonitrile/water (95:5) (K(SV) = 3.1 x 10(5) M(-1) for CP1a and 1.1 x 10(5) M(-1) for CP1b). Partial restoration of emission was observed upon exposure of Cu(II)-CP solutions to excess NO(g) in acetonitrile/water (95:5) or 10 mM SDS(aq).

2,2'-Dipyridyl↗
PubMed2006

Polymer-bound dirhodium tetracarboxylate films for fluorescent detection of nitric oxide.

A polymer-bound dirhodium complex, [{Rh2(O2CCH3)3(Ds-pip)}n(O2C-P)], was prepared via ligand exchange of [Rh2(O2CCH3)4] with the side chains of a methyl methacrylate/methacrylic acid copolymer (O2C-P) followed by axial coordination of the fluorophore, N-dansylpiperazine (Ds-pip). Emission from Ds-pip is quenched when coordinated to the dirhodium complex but can be restored upon displacement by analytes. Exposure of [{Rh2(O2CCH3)3(Ds-pip)}n(O2C-P)] films to aqueous nitric oxide (NO) evokes a 2.2-fold increase in integrated emission. The polymer matrix excludes potentially interfering analytes including reactive oxygen or nitrogen species, which cannot readily permeate the film.

Carboxylic Acids↗
PubMed2005

Conjugated polymer-based fluorescence turn-on sensor for nitric oxide.

A turn-on fluorescent sensor for NO (g) in solution was synthesized using a bipyridyl-substituted poly(p-phenylene vinylene) derivative (CP1) as the sensory scaffold. The action of NO (g) upon the CP1-Cu(II) complex reduces it to the CP1-Cu(I) complex with a concomitant 2.8-fold increase in emission intensity. The reagent is selective for NO (g) versus other biological reactive nitrogen species, except for nitroxyl, and has a detection sensitivity limit of 6.3 nM. [structure: see text]

Copper↗
PubMed2004

Conjugated polymers featuring heavier main group element multiple bonds: a diphosphene-PPV.

A new sterically encumbered bifunctional ligand has been developed, and its ability to provide simultaneous stabilization for two low-coordinate phosphorus centers has allowed the synthesis of new hybrid inorganic-organic conjugated materials. The new phosphaalkene polymers have been prepared from a diphospha-Wittig reagent and are exclusively E-configured about the P=C bonds. An unprecedented polymer having diphosphene (-P=P-) units in the polymer main chain is also reported. The soluble polymers were characterized by UV-visible and fluorescence spectroscopy, as well as by 1H and 31P NMR spectroscopy.

Journal Article↗
PubMed2003

Sterically encumbered diphosphaalkenes and a bis(diphosphene) as potential multiredox-active molecular switches: EPR and DFT investigations.

The reduction products of two diphosphaalkenes (1 and 2) and a bis(diphosphene) (3) containing sterically encumbered ligands and corresponding to the general formulas Ar-X=Y-Ar'-Y=X-Ar, have been investigated by EPR spectroscopy. Due to steric constraints in these molecules, at least one of the dihedral angles between the CXYC plane and either the Ar plane or the Ar' plane is largely nonzero and, hence, discourages conformations that are optimal for maximal conjugation of P=X (or P=Y) and aromatic pi systems. Comparison of the experimental hyperfine couplings with those calculated by DFT on model systems containing no cumbersome substituents bound to the aromatic rings shows that addition of an electron to the nonplanar neutral systems causes the X=Y-Ar'-Y=X moiety to become planar. In contrast to 1 and 2, 3 can be reduced to relatively stable dianion. Surprisingly the two-electron reduction product of 3 is paramagnetic. Interpretation of its EPR spectra, in the light of DFT calculations on model dianions, shows that in [3](2)(-) the plane of the Ar' ring is perpendicular to the CXYC planes. Due to interplay between steric and electronic preferences, the Ar-X=Y-Ar'-Y=X-Ar array for 3 is therefore dependent upon its redox state and acts as a "molecular switch".

Journal Article↗
PubMed2003

A fluorescent E-poly(p-phenylenephosphaalkene) prepared by a phospha-Wittig reaction.

A soluble (E)-poly(p-phenylenephosphaalkene) having sterically encumbering ligands has been prepared by a phospha-Wittig reaction. This material exhibits a bathochromic shift with respect to E-PPV and with respect to representative model oligomers. We also report the first fluorescence study of a poly(p-phenylenephosphaalkene) and find that this material exhibits fluorescence, though with modest intensity relative to similarly sized carbon-based analogues.

Journal Article↗
PubMed2003

An unusual equilibrium chlorine atom transfer process and its potential for assessment of steric pressure by bulky aryls.

An unusually facile intermolecular chlorine atom transfer process has been discovered between the phospha-Wittig reagents ArP=PMe3 and ArPCl2 (Ar is a sterically hindered aryl group). The atom transfer process is catalyzed by added PMe3. A mechanism is forwarded that is based upon a Me3P/Me3PCl2 couple that allows shuttling of chlorine atoms between ArP groups. This unique transfer process is exploited to evaluate the steric properties of aryl groups via an equilibrium process.

Journal Article↗
PubMed2002

Syntheses and structural characterizations of the unsymmetrical diphosphene DmpP=PMes* (Dmp =2,6-Mes(2)C(6)H(3), Mes* = 2,4,6-(t)Bu(3)C(6)H(2)) and the cyclotetraphosphane [DmpPPPh](2).

The new diphosphene DmpP=PMes* (Dmp = 2,6-Mes(2)C(6)H(3); Mes* = 2,4,6-(t)Bu(3)C(6)H(2), 1) having two different classes of sterically demanding aryls has been prepared and structurally characterized. This structure appears to be the first featuring both types of sterically demanding groups (a meta-terphenyl and Mes*) in a single molecule about a multiply bonded unit. Compound 1 features a P=P bond length of 2.024(13) A. The structure of 1 also allows comparisons to the two previously structurally characterized symmetric diphosphenes DmpP=PDmp and Mes*P=PMes*. The crystal structure of the cyclotetraphosphane [DmpPPPh](2) (3), the product of self-dimerization of the unstable diphosphene DmpP=PPh (2), has been determined. The structure of 3 demonstrates that a single bulky Dmp group is insufficient to prevent dimerization of 2. (31)P NMR data for all three compounds are also reported.

Journal Article↗