Photofabrication of two-dimensional quasi-crystal patterns on UV-curable molecular azo glass films

In this work, two-dimensional surface quasi-crystal patterns were developed by using a novel azobenzene-containing amorphous material (IAC-4), which was newly synthesized for the application. IAC-4 contains a core of isosorbide moiety and two push-pull type azo chromophores as the inner part. The periphery of IAC-4 is functionalized with four cinnamate groups, which can undergo [2+2] photocycloaddition reaction upon UV light irradiation. The molecular design can allow IAC-4 to readily form surface relief structures upon Ar+ laser irradiation, and the formed structures can be further stabilized through a photo-cross-linking reaction induced by UV light irradiation. On the basis of the material, two-dimensional (2D) quasi-crystal structures with different rotation symmetries were successfully fabricated on the IAC-4 films by using the dual-beam multiple exposure technique. In contrast to the approach using photoresist, the quasi-crystal structures were fabricated through the photoinduced mass migration, and no subsequent wet-etch or dry-etch step was required in the process. The quasi-crystal structures with rotation symmetry as high as 60-fold could be feasibly fabricated through this approach. The surface patterns and fabrication method can be potentially applied in areas such as optics, communications, and security inspection.     

Fluorescent film sensor for nitroaromatics prepared via grafting a conjugated polymer on a glass slide surface

A functionalized glass sensor (G-P) was prepared for detecting nitroaromatic compounds (NACs) by chemically immobilizing a conjugated polymer P on the surface of a glass slide. The monolayer film sensor had several advantages: the signal amplification effect of conjugated polymers, no leakage of sensing materials in solution, and good permeability for the analytes. Fluorescence quenching studies demonstrated that the sensor was highly sensitive to NACs. When the DNT concentration was 1.03 × 10^–7 mol/L, the quenching efficiency (1–I/I ₀) of G-P reached 52.8%. Moreover, the excellent properties of reversibility, selectivity and sensitivity indicated the glass G-P might be a promising sensor in the field of explosives detection.     

Rare earth-doped lead borate glasses and transparent glass-ceramics: structure-property relationship

Correlation between structure and optical properties of rare earth ions in lead borate glasses and glass-ceramics was evidenced by X-ray-diffraction, Raman, FT-IR and luminescence spectroscopy. The rare earths were limited to Eu(3+) and Er(3+) ions. The observed BO(3)?BO(4) conversion strongly depends on the relative PbO/B(2)O(3) ratios in glass composition, giving important contribution to the luminescence intensities associated to (5)D(0)-(7)F(2) and (5)D(0)-(7)F(1) transitions of Eu(3+). The near-infrared luminescence and up-conversion spectra for Er(3+) ions in lead borate glasses before and after heat treatment were measured. The more intense and narrowing luminescence lines suggest partial incorporation of Er(3+) ions into the orthorhombic PbF(2) crystalline phase, which was identified using X-ray diffraction analysis.     

Heterocycle-based isomeric chromophores with substantially varying NLO properties: a new structure-property correlation study

A number of heterocycle-based aromatic and quinonoid molecular systems have been considered for the theoretical study of their electric response properties. The nonlinear optical (NLO) parameters have been calculated by using the ab initio MO and DFT methods. An approximate scheme for calculating the first hyperpolarizability (beta) and second hyperpolarizability (gamma) in the framework of the sum-over-state (SOS) method have been proposed by exploiting the generalized Thomas-Kuhn sum rule (TK-SR). The NLO properties in the present scheme can be evaluated solely from the ground-state dipole moment (mu) and linear polarizability (alpha) and have been found to correlate fairly with the ab initio calculated values. The approximate scheme can be reasonably used to explain the wider range of variation of higher-order polarizabilities in terms of the above quantities. The position of the N atom in the thiazole ring at the ortho position (versus meta position) to the acceptor increases beta and decreases gamma for aromatic compounds, while the reverse trend is found with quinonoid compounds. In the case of the pyridine ring, the shifting of the N atom toward the acceptor enhances gamma, with insignificant variation of beta predicted for both the aromatic and quinonoid molecules. The negative contribution of the cubic polarizability of the quinonoid species increases linearly with alpha(2)/mean transition energy (Delta E).     

Diffusion of organic dyes in a niosome immobilized on a glass surface using fluorescence correlation spectroscopy

Giant multilameller niosomes containing cholesterol and triton X-100 are studied using fluorescence correlation spectroscopy (FCS). Dynamic light scattering (DLS) data indicates formation of niosomes of broadly two different sizes (diameter)--~150 nm and ~1300 nm. This is confirmed by field emission scanning electron microscopy (FE-SEM) and confocal microscopy. The diffusion coefficient (D(t)) of three organic dyes in the niosome immobilized on a glass surface is studied using fluorescence correlation spectroscopy. On addition of the room temperature ionic liquids (RTIL) (1-methyl-3-pentylimidazolium bromide, [pmim][Br] and 1-methyl- 3-pentylimidazolium tetra-fluoroborate, [pmim][BF(4)]) the size of the niosome particles increases. The D(t) of all the organic dyes (DCM, C343 and C480) increases on addition of RTILs, indicating faster diffusion. The viscosity calculated from the D(t) of the three dyes exhibits weak probe dependence. Unlike lipid or catanionic vesicle, the D(t) values in a niosome exhibit very narrow distribution. This indicates that the niosomes are fairly homogeneous with small variation of viscosity.     

Radical grafting from glass fiber surface: Graft polymerization of vinyl monomers initiated by azo groups introduced onto the surface

This paper describes the radical graft polymerization of vinyl monomers from glass fiber surface initiated by alkylazo groups introduced onto the fiber surface. The introduction of azo groups onto the glass fiber surface was achieved by reaction of isocyanate groups which were previously attached onto the surface with two kinds of azo initiators, 4,4′-azobis(4-cyanopentanoic acid) (ACPA) and 2,2′-azobis(2-cyanopropanol) (ACP). The amounts of surface azo groups introduced by ACPA and ACP were both determined to be 1.3 × 10⁻⁵ mol g⁻¹ by nitrogen analysis. The radical graft polymerization of methyl methacrylate (MMA) was found to be initiated in the presence of the glass fiber having surface azo groups. During the polymerization, part of resultant poly(MMA) grafted onto the fiber surface through propagation of the polymer from the surface radicals produced by the decomposition of the azo groups. The percentage of grafting of poly(MMA) reached 48.1% after 24 h. The graft polymerizations of other monomers, such as styrene, N-vinylcarbazole, and acrylic acid, were also initiated by the surface azo groups, and the corresponding polymer effectively grafted onto the surface. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2121–2128, 1999     

Photoinduced phospholipid polymer grafting on Parylene film: advanced lubrication and antibiofouling properties

Poly(p-xylylene) (Parylene C) coatings have been applied in implantable electronic devices because of their electrical insulation and moisture barrier properties. To provide lubrication and an antibiofouling surface, a biomimetic phospholipid polymer--poly(2-methacryloyloxyethyl phosphorylcholine (MPC))--was grafted from the surface using UV irradiation with benzophenone as an initiator. The poly(MPC) grafting on the Parylene C films was confirmed by attenuated total reflection-Fourier transfer inflated irradiation, X-ray photoelectron spectroscopy and ellipsometry. These analyses indicated that the Parylene C films were completely covered by the poly(MPC)-graft layer with an average thickness of 140 nm under dry condition. The atomic force microscope (AFM) images revealed that the poly(MPC)-graft chains extended under wet condition. However, they formed globular structures under dry condition. Water contact angle measurements revealed a decreased receding angle of 29.5 degrees on the poly(MPC)-grafted surface with a high hysteresis of 41.4 degrees. These results indicate that the poly(MPC)-graft chains gain mobility in a wet environment. The average kinetic friction coefficient of the poly(MPC)-grafted surface in water was 0.018, which was 90% lower than that of the original surface. The in vitro single protein adsorption reduced by over 70% due to the poly(MPC) grafting. The hydrated poly(MPC)-graft chains are considered to provide lubrication and antibiofouling properties. The surface zeta potential measurement clarified the electroneutrality of the poly(MPC)-grafted surface. We concluded that the poly(MPC) grafting from the Parylene C layer significantly improved its surface properties and, subsequently, its biological properties.     

Photoinduced surface dynamics of CO adsorbed on a platinum electrode

The surface dynamics of adsorbed CO molecules formed by dissociative adsorption of HCHO at a polycrystalline Pt electrode/electrolyte solution interface was studied by picosecond time-resolved sum-frequency generation (TR-SFG) spectroscopy. A SFG peak at 2050-2060 cm(-1) was observed at the Pt electrode in HClO(4) solution containing HCHO at 0-300 mV (vs Ag/AgCl), indicating the formation of adsorbed CO at an atop site of the Pt surface as a result of dissociative adsorption of HCHO. The peak position varied with potential by approximately 33 cm(-1)/V, as previously found in an infrared reflection absorption spectroscopy (IRAS) study. Irradiation of an intense picosecond visible pulse (25 ps, 532 nm) caused an instant intensity decrease and broadening of the CO peak accompanied by the emergence of a new broad peak at approximately 1980 cm(-1) within the time resolution of the system. These results suggest a decrease and increase in the populations of CO adsorbed on atop and bridge sites, respectively, upon visible pump pulse irradiation.     

High charge-carrier mobility in pi-deficient discotic mesogens: design and structure-property relationship

Hexaazatrinaphthylene (HATNA) derivatives with six alkylsulfanyl chains of different length (hexyl, octyl, decyl and dodecyl) have been designed to obtain new potential electron-carrier materials. The electron-deficient nature of these compounds has been demonstrated by cyclic voltammetry. Their thermotropic behaviour has been studied by means of differential scanning calorimetry and polarised optical microscopy. The supramolecular organisation of these discotic molecules has been explored by temperature-dependent X-ray diffraction on powders and oriented samples. In addition to various liquid crystalline columnar phases (Col(hd), Col(rd)), an anisotropic plastic crystal phase is demonstrated to exist. The charge-carrier mobilities have been measured with the pulse-radiolysis time-resolved microwave-conductivity technique. They are found to be higher in the crystalline than in the liquid crystalline phases, with maximum values of approximately 0.9 and 0.3 cm(2) V(-1) s(-1), respectively, for the decylsulfanyl derivative. Mobilities strongly depend on the nature of the side chains.     

Hydrazone comprising compounds as promising anti-infective agents: chemistry and structure-property relationship

Despite the adverse effects of microbial hazards on public health, major pharmaceutical firms have left the field of anti-infective development and a dramatic reduction in the number of researcher's intricated in the quest for new specific anti-infective leads. In the non-existence of an efficient forum for antibiotics development and over usage in human beings and animals, bacteria have demoralized this potential by gradually establishing the resistance toward most of the antibiotics used. Thus, the production of novel and successful anti-infective drugs is urgently required to combat this resistance. Hydrazones and hydrazides have mounted as a key-skeleton for the development of active drugs, due to their important biological and pharmacological profiles. Hydrazones are being manufactured as medicines by various investigators to fight against the ailments with maximal effects and minimal toxicity. This paper focuses on the outline of the literature results of recent years, incorporating the work on the anti-infective profile of hydrazone analogues. This review may also act as an excellent basis for the development of new derivatives of hydrazone as potential anti-infective mediators.     

Simple relationship between total molecular correlation energies and LMO sizes

As an alternative to the density functional approach to estimating total molecular correlation energies, the equation E_corr=?0.06593 ∑ R, where R_i=〈r²〉${}_{\text{i}}^{\text{½}}$ and i runs over the localized molecular orbitals was fitted to 25 STO -3G data points with a root-mean-square error of 0.025 hartree. Other more general equations were tried but no significant improvement was observed in the fit.     

Photoinduced electron-transfer processes along molecular wires based on phenylenevinylene oligomers: a quantum-chemical insight

Quantum-chemical techniques are applied to model the mechanisms of photoinduced charge transfer from a pi-electron donating group (tetracene, D) to a pi-electron-acceptor moiety (pyromellitimide, A) separated by a bridge of increasing size (p-phenylenevinylene oligomers, B). Correlated Hartree-Fock semiempirical approaches are exploited to calculate the four main parameters controlling the transfer rate (k(RP)) in the framework of Marcus-Jortner-Levich's formalism: (i) the electronic coupling between the initial and final states; (ii) and (iii) the internal and external reorganization energy terms; and (iv) the variation of the free Gibbs energy. The charge transfer is shown to proceed in these compounds through two competing mechanisms, coherent (superexchange) versus incoherent (bridge-mediated) pathways. While superexchange is the dominant mechanism for short bridges, incoherent transfer through hopping along the phenylene vinylene segment takes over in longer chains (for ca. three phenylenevinylene repeat units). The influence of the chemical structure of the pi-conjugated phenylenevinylene bridge on the electronic properties and the rate of charge transfer is also investigated.     

Computer simulation study of pattern transfer in AB diblock copolymer film adsorbed on a heterogeneous surface

In this work we investigate how a pattern imposed in a copolymer film at a certain distance from the surface propagates through the film onto an adsorbing heterogeneous surface. We bias the copolymer film to adopt a specified target pattern and then use simulation to design a surface pattern that helps the adsorbed film to maintain that target pattern. We examine the effect of varying the copolymer chain length, the size of the target pattern, and the distance from the surface where the target pattern is applied, z', on the extent of pattern transfer. For each chain length, target pattern, and z' we compare the energy of the system when a pattern is applied in the bulk to the energy when no pattern is applied in order to understand why a certain pattern size is transferred to the surface with higher fidelity than the others. At constant chain length, pattern transfer is best when the pattern size brings the energy of the system close to the energy when no pattern is applied. At constant pattern size, pattern transfer is best in the systems with longer chains. This is because longer chains are more likely to adsorb as brushes and loops which then helps transfer the pattern through the adsorbed film down to the surface.     

Steric blocking as a tool to control molecular film geometry at a metal surface

The application of steric blocking in surface science is exemplified by the control of surface patterns through the selective methylation of pentacenetetrone. Pentacenetetrones interact (with one another) on Cu(111) via intermolecular hydrogen bonding involving the carbonyl oxygen and the adjacent hydrogen atoms. Steric blocking of the intermolecular interaction by the successive insertion of inert methyl groups at terminal locations transforms a dense molecular pattern first into isolated double rows and eventually into single rows in a highly predictable fashion. Density functional theory modeling reveals the underlying energetics.     

Photoinduced hinge-like molecular motion: studies on xanthene-based cyclic azobenzene dimers

[Structure: see text]. Molecular devices incorporating azobenzene units represent active components of smart systems, as they are capable of exhibiting photoregulated cooperative molecular motion. Herein, we describe the synthesis, X-ray crystal analysis, and photochemical and thermal studies of a xanthene based cyclic azobenzene dimer and its precursor. The trans-trans isomer of the azobenzene dimer upon photoirradiation transforms to the cis-cis isomer through an intermediate trans-cis isomer. The X-ray crystal structures of the trans-trans isomer (open) and the cis-cis isomer (closed) provide unambiguous proof for the hinge-like molecular motion in this class of molecules. The inferences drawn from photochemical and thermal studies shed light on the effect of varied substitution and cyclic structures on the different transitions. The lifetime of the cis-cis isomer is estimated to be 6.43 years, whereas the trans-cis isomer is short-lived (2.73 min) at 303 K. A rational explanation for the relative stability of the different isomers is derived from the isokinetic plot and theoretical calculations.