Biomedical subjects

Pulak Dutta

Publications and source records attributed to Pulak Dutta.

12 recordsLinked to original sources

PubMed2006

Aggregation-governed oriented growth of inorganic crystals at an organic template.

X-ray studies performed during the growth of CdCO(3) and MnCO(3) crystals from supersaturated aqueous solutions, at fatty acid monolayer templates, reveal that the nucleates are nearly three-dimensional powders below a threshold supersaturation. However, at higher supersaturations, the crystals are preferentially oriented with the {0 1 2} direction vertical. Scanning electron microscope images of samples transferred to substrates show discrete crystals at low concentrations, while at higher concentrations the crystals self-aggregate to form linear chains and sheets. The authors speculate that preferential alignment at the organic-inorganic interface is enhanced as a consequence of oriented aggregation of crystals. The role of monolayer-ion interactions in governing the morphologies and the resulting orientation of the inorganic nucleate is discussed.

Alcohols↗

PubMed2006

X-ray reflectivity study of ultrathin liquid films of diphenylsiloxane-dimethylsiloxane copolymers.

Using X-ray reflectivity, we observe drastic differences in the interfacial structure and molecular ordering of diphenylsiloxane-dimethylsiloxane copolymer thin films deposited on hydroxylated versus H-terminated (etched) silicon wafers. We find that substrate type and comonomer ratio determine the conformational arrangements in these liquid films. High-energy bonding between the substrate and the molecules and an increase in rigidity of the molecules due to replacement of methyl groups by phenyl groups leads to a specific molecular ordering at the liquid/solid interface and pronounced density oscillations in this region. The observed structural reorganizations are explained by the interplay and the established balance between the chain flexibility and the polymer-substrate interactions.

Journal Article↗

PubMed2006

Controlling structure from the bottom-up: structural and optical properties of layer-by-layer assembled palladium coordination-based multilayers.

Layer-by-layer assembly of two palladium coordination-based multilayers on silicon and glass substrates is presented. The new assemblies consist of rigid-rod chromophores connected by terminal pyridine moieties to palladium centers. Both colloidal palladium and PdCl2(PhCN)2 were used in order to determine the effect of the metal complex precursor on multilayer structure and optical properties. The multilayers were formed by an iterative wet-chemical deposition process at room temperature in air on a siloxane-based template layer. Twelve consecutive deposition steps have been demonstrated resulting in structurally regular assemblies with an equal amount of chromophore and palladium added in each molecular bilayer. The optical intensity characteristics of the metal-organic films are clearly a function of the palladium precursor employed. The colloid-based system has a UV-vis absorption maximum an order of magnitude stronger than that of the PdCl2-based multilayer. The absorption maximum of the PdCl2-based film exhibits a significant red shift of 23 nm with the addition of 12 layers. Remarkably, the structure and physiochemical properties of the submicron scale PdCl2-based structures are determined by the configuration of the approximately 15 angstroms thick template layer. The refractive index of the PdCl2-based film was determined by spectroscopic ellipsometry. Well-defined three-dimensional structures, with a dimension of 5 microm, were obtained using photopatterned template monolayers. The properties and microstructure of the films were studied by UV-vis spectroscopy, spectroscopic ellipsometry, atomic force microscopy (AFM), X-ray reflectivity (XRR), scanning electron microscopy (SEM), and aqueous contact angle measurements (CA).

Journal Article↗

PubMed2006

X-Shaped electro-optic chromophore with remarkably blue-shifted optical absorption. Synthesis, characterization, linear/nonlinear optical properties, self-assembly, and thin film microstructural characteristics.

A novel type of "X-shaped" two-dimensional electro-optic (EO) chromophore with extended conjugation has been synthesized and characterized. This chromophore is found to exhibit a remarkably blue-shifted optical maximum (357 nm in CH(2)Cl(2)) while maintaining a very large first hyperpolarizability (beta). Hyper-Rayleigh Scattering (HRS) measurements at 800 nm provide a beta(zzz) value of 1840 x 10(-30) esu. Self-assembled thin films of this chromophore were fabricated via a layer-by-layer chemisorptive siloxane-based approach. The chromophoric multilayers have been characterized by transmission optical spectroscopy, advancing contact angle measurements, synchrotron X-ray reflectivity, atomic force microscopy, and angle-dependent polarized second harmonic generation spectroscopy. The self-assembled chromophoric films exhibit a dramatically blue-shifted optical maximum (325 nm) while maintaining a large EO response (chi(2)(333) approximately 232 pm/V at 1064 nm; r(33) approximately 45 pm/V at 1310 nm). This work demonstrates an attractive approach to developing EO materials offering improved nonlinearity-transparency trade-offs.

Journal Article↗

PubMed2006

Observation of surface layering in a nonmetallic liquid.

Oscillatory density profiles (layers) have previously been observed at the free surfaces of liquid metals but not in other isotropic liquids. We have used x-ray reflectivity to study a molecular liquid, tetrakis(2-ethylhexoxy)silane. When cooled to T/Tc approximately 0.25 (well above the freezing point for this liquid), density oscillations appear at the surface. Lateral order within the layers is liquidlike. Our results confirm theoretical predictions that a surface-layered state will appear even in dielectric liquids at sufficiently low temperatures, if not preempted by freezing.

Journal Article↗

PubMed2006

Strategies for electrooptic film fabrication. Influence of pyrrole-pyridine-based dibranched chromophore architecture on covalent self-assembly, thin-film microstructure, and nonlinear optical response.

The new dibranched, heterocyclic "push-pull" chromophores bis{1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (1), 1-(pyrid-4-yl)-2-(N-methyl-5-formylpyrrol-2-yl)ethylene (2), {1-(N-methylpyridinium-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}{(1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane (3), N-methyl-2-[1-(N-methylpyrid-4-yl)ethen-2-yl]-5-[pyrid-4-yl]ethen-2-yl]pyrrole iodide (4), bis{1-(N-methyl-4-pyridinio)-2-[2-(N-methylpyrrol-5-yl)]ethane}methane iodide (5), and N-methyl-2,5-[1-(N-methylpyrid-4-yl)ethen-2-yl]pyrrole iodide (6) have been synthesized and characterized. The neutral (1 and 2) and monomethyl salts (3 and 4) undergo chemisorptive reaction with iodobenzyl-functionalized surfaces to afford chromophore monolayers SA-1/SA-2 and SA-3/SA-4, respectively. Molecular structures and other physicochemical properties have been defined by (1)H NMR, optical spectroscopy, and XRD. Thin-film characterization by a variety of techniques (optical spectroscopy, specular X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and angle-dependent polarized second harmonic generation) underscore the importance of the chromophore molecular architecture as well as film growth method on film microstructure and optical/electrooptic response.

Journal Article↗

PubMed2005

Photoinduced deprotection and ZnO patterning of hydroxyl-terminated siloxane-based monolayers.

Trimethoxy-[11-(2-nitrobenzyloxy)undecyl]silane (1) and trimethoxy-[17-(2-nitrobenzyloxy)heptadecyl]silane (2) have been used for the covalent assembly of siloxane-based photopatternable monolayers. Exposing the monolayers to UV light (312 +/- 10 nm) results in the generation of reactive hydroxyl-terminated monolayers without affecting the film quality. The new monolayers, deprotection chemistry, and the effect of photoinduced headgroup lift-off on the monolayer microstructure have been studied in detail by a full complement of physicochemical techniques, including optical (UV-vis) spectroscopy, ellipsometry, aqueous contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), synchrotron X-ray reflectivity (XRR), and atomic force microscopy (AFM and AFM-force spectroscopy). AFM-force spectroscopy was used to analyze hydrogen-bond interactions as a function of the nature of the solid-liquid interface. AFM-force spectroscopy indicates a hydrogen-bond energy for photodeprotected monolayers of 8.2 kJ mol(-1) (approximately 2 kcal mol(-1)). Scanning electron microscopy (SEM) revealed that treatment of photopatterned monolayers with ZnEt2 solutions resulted in well-defined approximately 2 microm x 2 microm features of 10 A thick ZnO layers.

Journal Article↗

PubMed2005

Covalently bound hole-injecting nanostructures. Systematics of molecular architecture, thickness, saturation, and electron-blocking characteristics on organic light-emitting diode luminance, turn-on voltage, and quantum efficiency.

Hole transporting materials are widely used in multilayer organic and polymer light-emitting diodes (OLEDs, PLEDs, respectively) and are indispensable if device electroluminescent response and durability are to be truly optimized. This contribution analyzes the relative effects of tin-doped indium oxide (ITO) anode-hole transporting layer (HTL) contact versus the intrinsic HTL materials properties on OLED performance. Two siloxane-based HTL materials, N,N'-bis(p-trichlorosilylpropyl)-naphthalen-1-yl)-N,N'-diphenyl-biphenyl-4,4'-diamine (NPB-Si(2)) and 4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPD-Si(2)), are designed and synthesized. They have the same hole transporting triarylamine cores as conventional HTL materials such as 1,4-bis(1-naphthylphenylamino)biphenyl (NPB) and N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl)-4,4-diamine (TPD), respectively. However, they covalently bind to the ITO anode, forming anode-HTL contacts that are intrinsically different from those of the anode to TPD and NPB. Applied to archetypical tris(8-hydroxyquinolato)aluminum(III) (Alq)-based OLEDs as (1) the sole HTLs or (2) anode-NPB HTL interlayers, NPB-Si(2) and TPD-Si(2) enhance device electroluminescent response significantly versus comparable devices based on NPB alone. In the first case, OLEDs with 36 000 cd/m(2) luminance, 1.6% forward external quantum efficiency (eta(ext)), and 5 V turn-on voltages are achieved, affording a 250% increase in luminance and approximately 50% reduction in turn-on voltage, as compared to NPB-based devices. In the second case, even more dramatic enhancement is observed (64 000 cd/m(2) luminance; 2.3% eta(ext); turn-on voltages as low as 3.5 V). The importance of the anode-HTL material contact is further explored by replacing NPB with saturated hydrocarbon siloxane monolayers that covalently bind to the anode, without sacrificing device performance (30 000 cd/m(2) luminance; 2.0% eta(ext); 4.0 V turn-on voltage). These results suggest new strategies for developing OLED hole transporting structures.

Journal Article↗

PubMed2005

High-performance hole-transport layers for polymer light-emitting diodes. Implementation of organosiloxane cross-linking chemistry in polymeric electroluminescent devices.

This contribution describes an organosiloxane cross-linking approach to robust, efficient, adherent hole-transport layers (HTLs) for polymer light-emitting diodes (PLEDs). An example is 4,4'-bis[(p-trichlorosilylpropylphenyl)phenylamino]biphenyl (TPDSi(2)), which combines the hole-transporting efficiency of N,N-diphenyl-N,N-bis(3-methylphenyl)-1,1-biphenyl)-4,4-diamine) (TPD, prototypical small-molecule HTL material) and the strong cross-linking/densification tendencies of organosilanol groups. Covalent chemical bonding of TPDSi(2) to PLED anodes (e.g., indium tin oxide, ITO) and its self-cross-linking enable fabrication of three generations of insoluble PLED HTLs: (1) self-assembled monolayers (SAMs) of TPDSi(2) on ITO; (2) cross-linked blend networks consisting of TPDSi(2) + a hole transporting polymer (e.g., poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl))diphenylamine), TFB) on ITO; (3) TPDSi(2) + TFB blends on ITO substrates precoated with a conventional PLED HTL, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS). PLED devices fabricated using these new HTLs exhibit comparable or superior performance vs comparable devices based on PEDOT-PSS alone. With these new HTLs, current efficiencies as high as approximately 17 cd/A and luminances as high as approximately 140,000 cd/m(2) have been achieved. Further experiments demonstrate that not only do these HTLs enhance PLED anode hole injection but they also exhibit significantly greater electron-blocking capacity than PEDOT-PSS. The present organosiloxane HTL approach offers many other attractions such as convenience of fabrication, flexibility in choosing HTL components, and reduced HTL-induced luminescence quenching, and can be applied as a general strategy to enhance PLED performance.

Journal Article↗

PubMed2003

Molecularly "engineered" anode adsorbates for probing OLED interfacial structure-charge injection/luminance relationships: large, structure-dependent effects.

Molecule-scale structure effects at organic light-emitting diodes (OLED) anode-organic transport layer interfaces are probed via a self-assembly approach. A series of ITO anode-linked silyltriarylamine molecules differing in aryl group and linker density are synthesized for this purpose and used to probe the relationship between nanoscale interfacial chemical structure, charge injection and electroluminescence properties. Dramatic variations in hole injection magnitude and OLED performance can be correlated with the molecular structures and electrochemically derived heterogeneous electron-transfer rates of such triarylamine fragments, placed precisely at the anode-hole transport layer interface. Very bright and efficient ( approximately 70 000 cd/m2 and approximately 2.5% forward external quantum efficiency) OLEDs have thereby been fabricated.

Journal Article↗

PubMed2003

Vapor phase self-assembly of electrooptic thin films via triple hydrogen bonds.

The donor-acceptor pi-electron chromophore 5-{4-[2-(4,6-diamino-[1,3,5]triazin-2-yl)-vinyl]-benzylidene}-pyrimidine-2,4,6-trione (DTPT) was designed and synthesized. Triple H-bonding interactions between neighboring molecules direct self-assembled chromophore alignment in a head-to-tail orientation using a straightforward vapor phase deposition process. Angle-dependent SHG interference patterns and the quadratic dependence of the 532 nm light output intensity on the thickness of the DTPT films for glass substrates coated on both sides demonstrate high, reproducible film quality and uniformity. XRD also demonstrates long-range order in the film and yields a molecular tilt angle in good agreement with polarized SHG data, clearly showing that out-of-plane ordering of chromophore molecules has been achieved.

Journal Article↗

PubMed2002

Evidence of registry at the interface during inorganic nucleation at an organic template.

In situ synchrotron x-ray diffraction studies of the nucleation of barium fluoride from supersaturated solutions, at fatty-acid monolayer templates, reveal a commensurate relationship between the interfacial lattices of the organic molecules and the inorganic atoms. At the onset of growth, the barium fluoride layer is very thin and the lateral unit cell is contracted by as much as 4%; at the same time the organic molecules tilt, expanding the organic unit cell. This flexibility is what allows the lattice parameters to be commensurate. Such registry is expected to play an important precursor role in controlled biomineralization and organic-matrix-mediated materials synthesis.

Barium Compounds↗