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Seth R Marder

Publications and source records attributed to Seth R Marder.

29 records · Page 2Linked to original sources
PubMed2004

Cubic liquid-crystalline nanoparticles.

Cubic liquid-crystalline nanoparticles prepared from aqueous dispersions of cubic lipid-water phases are kinetically stable in the presence of certain dispersing agents. The properties of cubic nanoparticles from monoolein-water and other lipid-water systems have been examined with a variety of experimental techniques. The cubic nanoparticles can be stabilized by polymerization of the reactive lipids in cubic lipid assemblies. Several low-energy-input methods have been developed to facilitate the production and application of cubic nanoparticles. The ability to incorporate and deliver lipophilic, amphiphilic, and water-soluble molecules in a controlled manner and the good biocompatibility of cubic nanoparticles make them excellent candidates for drug-delivery applications.

Journal Article↗
PubMed2004

Metal-ion sensing fluorophores with large two-photon absorption cross sections: aza-crown ether substituted donor-acceptor-donor distyrylbenzenes.

Chromophores based on a donor-acceptor-donor structure possessing a large two-photon absorption cross section and one or two mono-aza-15-crown-5 ether moieties, which can bind metal cations, have been synthesized. The influence of Mg(2+) binding on their one- and two-photon spectroscopic properties has been investigated. Upon binding, the two-photon action cross sections at 810 nm decrease by a factor of up to 50 at high Mg(2+) concentrations and this results in a large contrast in the two-photon excited fluorescence signal between the bound and unbound forms, for excitation in the range of 730 to 860 nm. Experimental and computational results indicate that there is a significant reduction of the electron donating strength of the aza-crown nitrogen atom(s) upon metal ion binding and that this leads to a blue shift in the position as well as a reduction in the strength of the lowest-energy two-photon absorption band. The molecules reported here can serve as models for the design of improved two-photon excitable metal-ion sensing fluorophores.

Aza Compounds↗
PubMed2004

Two-photon absorption in linear bis-dioxaborine compounds-the impact of correlation-induced oscillator-strength redistribution.

Quantum-chemical calculations of the two-photon absorption (TPA) cross-sections are used to determine the characteristics of the electronic excited states responsible for the observed peaks in the TPA spectra of two bis-dioxaborine-substituted biphenyl derivatives. We find two distinct TPA-active states with very different TPA cross-sections: the difference is explained on the basis of electron correlation. These effects, on the one hand, lead to TPA cross-sections of up to 500 x 10(-50) cm4 s photon(-1) for the state favored by correlation; on the other hand, they limit the overall cross-sections achievable in this class of materials.

Journal Article↗
PubMed2004

Electronic couplings in organic mixed-valence compounds: the contribution of photoelectron spectroscopy.

We show that the electronic coupling in strongly coupled organic mixed-valence systems can be effectively probed by means of gas-phase ultraviolet photoelectron spectroscopy (UPS). Taking six diamines as examples, the UPS estimates for the electronic couplings H(ab) are compared with the corresponding values determined from the intervalence charge-transfer absorption bands and from electronic structure calculations. Similar trends are observed for the H(ab) values estimated from UPS and optical spectra; this provides support for the applicability of Hush theory to strongly coupled organic mixed-valence systems. The UPS electronic couplings are found to be somewhat smaller than those from optical spectroscopy, which is attributed to the role of vibronic coupling to symmetrical modes; when corrected for this vibronic coupling, the UPS H(ab) estimates confirm that triarylamine-based mixed-valence systems are close to the class-II/class-III borderline.

Journal Article↗
PubMed2003

N,N-dimethyl-N'-[(1E,2E)-3-(4-nitrophenyl)prop-2-enylidene]benzene-1,4-diamine and N,N-dimethyl-4-[(1E,3E)-4-(4-nitrophenyl)buta-1,3-dienyl]-1-naphthylamine.

Syntheses and X-ray structural investigations have been carried out for the two title compounds, viz. C(17)H(17)N(3)O(2), (I), and C(22)H(20)N(2)O(2), (II). The molecular skeleton of (I) is slightly non-planar; the dihedral angles between the conjugated linkage and the p-(dimethylamino)phenyl ring, and between the linkage and the p-nitrophenyl ring are 13.0 (2) and 13.8 (2) degrees, respectively. The dihedral angle between the slightly pyramidal dimethylamine substituent and the aromatic ring is 23.3 (1) degrees. The molecular skeleton of (II) is not planar; the dihedral angles between the conjugated linkage and the naphthalene ring, and between the linkage and the substituted phenyl ring are 36.1 (2) and 2.7 (3) degrees, respectively. The dimethylamine substituent in (II) has a pyramidal geometry; the dihedral angle between this substituent and the naphthalene ring is 71.7 (1) degrees. The dihedral angle between the nitro group and the plane of the substituted phenyl ring is 9.0 (3) degrees. There is a weak intermolecular C-H.O hydrogen bond in the crystal structure of (II), which links the molecules into centrosymmetric dimers. Molecular mechanics calculations of molecular conformations have shown that the crystal environment influences the conformation more in (I) than in (II).

Journal Article↗
PubMed2003

Ultrabright supramolecular beacons based on the self-assembly of two-photon chromophores on metal nanoparticles.

Silver nanoparticles coated with a self-assembled layer of approximately 2500 chromophoric alkylthiol ligands, that exhibit a huge per particle two-photon absorption cross section (2.7 x 10-45 cm4 s photon-1) and a high fluorescence quantum yield (0.33), are reported. Polyfunctionalized variants of these nanoparticles have been produced that show reasonable solubility in water/ethanol mixtures. By virtue of the large number of tethered chromophores, these particles act as strongly two-photon absorbing nanobeacons and may have applications in fluorescence imaging and sensing.

Absorptiometry, Photon↗
PubMed2002

Polymerized bicontinuous cubic nanoparticles (cubosomes) from a reactive monoacylglycerol.

Bicontinuous cubic phases of monoacylglycerides/Poloxamer 407 (PEO98PPO67PEO98)/water can be dispersed into submicron particles, which are termed "cubosomes". Technological applications of these nanoparticles may be possible, if their nonlamellar architecture can be rendered more robust. To accomplish this goal, a polymerizable heterobifunctional monoacylglycerol, 3-(2,4,13-(E,E)-tetradecatrienoyl)-sn-glycerol (1), was synthesized and combined with water to form an optically transparent gel. In the presence of Poloxamer 407 and excess water the cubic phase of 1 was dispersed by ultrasonication into 300-nm diameter nanoparticles. The polymerization of these reactive cubosomes could be initiated either by the use of a photoinitiator or with redox chemistry. The polymerized cubosomes remained stable even after the addition of excess Triton X-100, in a manner consistent with executing cross-linking in the nanostructures.

Cross-Linking Reagents↗
PubMed2002

Metallocene-terminated allylium salts: the effect of end group on localization in polymethines.

A range of 1,3-di(metallocenyl)allylium salts [Mc(CH)(3)Mc'](+)[X](-) [Mc, Mc' = ferrocenyl (Fc), 2,3,4,5,1',2',3',4'-octamethylferrocen-1-yl (Fc' '), ruthenocenyl (Rc); X = BF(4), PF(6)] was synthesized by reaction of (2-lithiovinyl)metallocenes with formylmetallocenes, followed by treatment of the resulting alcohols with HX. Two salts with X = BAr'(4) [Ar' = 3,5-(CF(3))(2)C(6)H(3)] were synthesized by anion metathesis from the corresponding PF(6) salts. The crystal structure of [Fc' '(CH)(3)Fc' '](+)[PF(6)](-) contains symmetrical termethine cations, while the same appears to be true in the disordered structure of [Fc(CH)(3)Fc](+)[PF(6)](-). The formally unsymmetrical cation in [Fc(CH)(3)Fc' '](+)[BF(4)](-) is only slightly unsymmetrical with little bond-length alternation in the allylium bridge. In contrast, the crystal structures of [Rc(CH)(3)Rc](+)[PF(6)](-) and [Rc(CH)(3)Rc](+)[BAr'(4)](-) both contain a bond-alternated "Peierls-distorted" cation, which can be considered as a ruthenocene bridged to a [(eta(6)-fulvene)(eta(5)-cyclopentadienyl)ruthenium] cation by a vinylene moiety. The strong similarity between solid-state and solution infrared and Raman spectra of [BF(4)](-), [PF(6)](-), and [BAr'(4)](-) salts of [Rc(CH)(3)Rc](+) indicates that the C-C stretching constant in the allylium chain and, therefore, the structure, of this ion are largely independent of the local environment, suggesting that the unsymmetrical structures observed in the crystal structures are not simply an artifact of packing. Differences in the solvatochromism of [Rc(CH)(3)Rc](+) and [Fc(CH)(3)Fc](+) also suggest a localized structure for the former cation in solution. Electrochemistry, UV-visible-NIR spectroscopy, and DF calculations give insight into the electronic structure of the metallocene-terminated allylium cations. Using an analogy between polymethines and mixed-valence compounds, the difference between the behaviors of [Fc(CH)(3)Fc](+) and [Rc(CH)(3)Rc](+) is attributed to larger reorganization energy associated with the geometry differences between metallocene and [(eta(6)-fulvene)(eta(5)-cyclopentadienyl)metal] structures in the ruthenium case.

Journal Article↗
PubMed2002

An efficient two-photon-generated photoacid applied to positive-tone 3D microfabrication.

A two-photon-activatable photoacid generator, based on a bis[(diarylamino) styryl]benzene core with covalently attached sulfonium moieties, has been synthesized. The photoacid generator has both a large two-photon absorption cross section (delta = 690 x 10(-50) centimeter(4) second per photon) and a high quantum yield for the photochemical generation of acid (phiH+ = 0.5). Under near-infrared laser irradiation, the molecule produces acid after two-photon excitation and initiates the polymerization of epoxides at an incident intensity that is one to two orders of magnitude lower than that needed for conventional ultraviolet-sensitive initiators. This photoacid generator was used in conjunction with a positive-tone chemically amplified resist for the fabrication of a three-dimensional (3D) microchannel structure.

Journal Article↗
PubMed2002

Efficient photoacids based upon triarylamine dialkylsulfonium salts.

New triarylamine dialkylsulfonium salts that are photosensitive in the near-ultraviolet have been prepared. The quantum yields of photoacid generation were found to be approximately 0.5 and are independent of the counterion. On the other hand, the efficiencies of the sulfonium salts toward the photopolymerization of cyclohexene oxide depend on the counterion and the sulfonium substituents. Photopolymerization kinetic studies demonstrate that these triphenylamine sulfonium salts are highly efficient cationic photoinitiators.

Journal Article↗