Role of chain length and spacers in the organization of long chain Schiff base compounds at air/water and solid/liquid interfaces

Langmuir films of long chain Schiff base compounds: N-(4-fluorobenzylidene)hexadecanamine (compound 1), N-(4-fluorobenzylidene)octadecanamine (compound 2) and 4-{[(4-fluorobenzylidene)amino]methyl}-N-hexadecylaniline (compound 3) have been studied at air/water interface using the characteristic surface pressure-molecular area (π-A) and surface potential-molecular area (ΔV-A) isotherms. Photoelastic modulated Fourier transform infrared spectroscopy has been used to analyze the films of the three compounds at air/water interface. The Langmuir-Blodgett films of these compounds have been characterized using X-ray diffraction that shows layered structures, with interlayer distances of up to 4.4 nm for compound 3. The results show that the layer-to-layer distance can be easily and rationally designed by choosing alkyl chains of different lengths and spacer. Compound 3 packs in an interdigitated bilayer structure with longer lamellar spacing whereas compounds 1 and 2 show a noninterdigitated monolayer structure. Atomistic model calculations have been carried out on the three compounds and the dipole moment values obtained agreed well with the experimental results of surface potential in Langmuir films. Among the three compounds, compound 3 forms stable vesicles spontaneously at room temperature.     

Near-infrared luminescent polymer thin films containing Yb(III) complex and photosensitized dye

Polymethylmethacrylate (PMMA) thin films containing Yb(pms)₃(H₂O)₈ (pms: bis(perfluoromethanesulfonyl)imide) and dipyridophenazine with DMSO and DMSO-d₆ were fabricated on the glass substrates. The films show photosensitized near-IR luminescence under UV light irradiation of 370 nm in wavelength. The emission quantum yields of Yb(III) complex in PMMA (film 1), PMMA containing DMSO (film 2), and PMMA containing DMSO-d₆ (film 3) thin films are 0.18, 0.26, and 0.26%, respectively. The emission quantum yields of films 1 and 2 were considerably enhanced after the annealing at 80 °C.     

Synthesis and characterization of electrochromic poly(amide–imide)s bearing methoxy-substituted triphenylamine units

New poly(amide–imide)s (PAIs) 3a–d and 3′a–d with methoxy-substituted triphenylamine (TPA) units were prepared by the direct polycondensation from various imide ring-preformed dicarboxylic acids 2a–d with 4,4′-diamino-2″,4″-dimethoxytriphenylamine (1) and 4,4′-diamino-4″-methoxytriphenylamine (1′), respectively, using triphenyl phosphite and pyridine as condensing agents. For the comparative study, the referenced PAIs 3″a–d without methoxy substituents on the TPA unit were also prepared from 2a–d with 4,4′-diaminotriphenylamine (1″). All the polymers were readily soluble in many organic solvents and could be solution-cast into tough and flexible polymer films. The glass-transition temperatures (T_gs) of these PAIs ranged from 196 to 298 °C and the 10% weight-loss temperatures were in excess of 445 °C in nitrogen. Cyclic voltammograms of the PAI films cast onto the indium–tin oxide (ITO)-coated glass substrate exhibit one reversible oxidation redox couples at 0.73–0.89 V vs. Ag/AgCl in an electrolyte/acetonitrile solution. The polymer films revealed good electrochemical and electrochromic stability, with coloration change from a pale yellow neutral form to a green oxidized form. After over 100 redox cycles, the polymer films still exhibited good redox and electrochromic reversibility. The 3 and 3′ series PAIs exhibited enhanced redox-stability and electrochromic performance as compared to the parent 3″ analogs without methoxy substituents on the TPA unit.     

Optical and morphological characterization by atomic force microscopy of luminescent 2-styrylpyridine derivative compounds with Poly(N-vinylcarbazole) films

The present work addresses the optical and morphological properties of organic films based on low molecular weight dyes styrylpyridine derivatives 2-styrylpyridine (A), 4-chlorophenyl-2-vinylpyridine (B) and 4-fluorophenyl-2-vinylpyridine (C), embedded in a polymeric matrix poly(N-vinylcarbazole) (PVK). The films were prepared by a spin-coating technique from solutions with dye:PVK ratios of 0.25:1, 0.5:1 and 1:1. Solvents were chloroform and toluene. The molar absorption coefficient (ε) spectra for a dye:PVK mixture in solution were a combination of the absorptions of both components separately, but for the deposited films, the shape of the spectrum showed that the poly(N-vinylcarbazole) absorption dominated. However, when the same films were dissolved again in CHCl₃, their spectra showed an absorption shape similar to that of the solution mixture before the deposition. Solution viscosity measurements were carried out with an Ubbelohde glass capillary viscometer to corroborate the results that showed a better mixture of the dye with the host in chloroform. The morphology of the prepared films was analyzed by atomic force microscopy and exhibited a solvent effect, with a pinhole-free, smooth surface when toluene was used and a wavy surface with chloroform. The ratio dye:matrix was the principal parameter for obtaining optical quality films; for 0.25:1 and 0.5:1 ratios, the films were of good quality, but for 1:1, the dye was expelled from the PVK and a crystallization was present over the surface of the films. Film thickness was also measured and films deposited from toluene solutions gave an average thickness of 54 nm while films from chloroform solutions had an average thickness greater than 160 nm that increased depending on chromophore concentration.     

Efficient bulk heterojunction solar cells based on D–A copolymers as electron donors and PC70BM as electron acceptor

Two low band gap conjugated polymers P1 (alternating phenylenevinylene containing thiophene and pyrrole rings) and P2 (alternating phenylenevinylene with dithenyl (thienothiadiazole) segments) having optical band gap 1.65 eV and 1.74 eV, respectively, were used as electron donor along with the PC₇₀BM as electron acceptor for the fabrication of bulk heterojunction solar cells. The power conversion efficiency (PCE) of BHJ devices based on P1:PC₇₀BM and P2:PC₇₀BM cast from THF solvent is about 2.84% and 2.34%, respectively, which is higher than the BHJ based on PCBM as electron acceptor. We have investigated the effect of mixed (1-chloronaphthalene (CN)/THF) solvent, modification of PEDOT:PSS layer and inserting of TiO₂ layer, on the photovoltaic performance of polymer solar cell. We have achieved power conversion efficiency of 5.07% for the polymer solar cells having structure ITO/PEDOT:PSS (modified)/P1:PC₇₀BM (CN/THF cast)/TiO₂/Al. The effect of solvent used for spin coating, modification of PEDOT:PSS layer and inclusion of TiO₂ layer has been discussed in detail.     

Cationic triblock copolymer micelles deliver anionic spacer chains substituted aluminum phthalocyanine for enhancement intracellular photodynamic efficacy

A novel spacer chains substituted aluminum phthalocyanine (Pc), naming tetra-carboxylaminohexanoicsulfonyl aluminium phthalocyanine 4 was synthesized. Its structure was characterized by elemental analysis, IR, ¹H NMR and MS. Polyion complex micelle (PIC) between the 4 and amphiphilic triblock copolymer poly(L-lysin)-block-poly(ethylene glycol)-block-poly(L-lysin) (PLL-b-PEG-b-PLL) was formed via an electrostatic interaction between the positively charged poly(L-lysin)(PLL) segment and negatively charged periphery of the 4. Dynamic light scattering (DLS) and atom force microscopy (AFM) image showed that 4-loaded PIC formed a spherical nanocarrier micelle with approximately 85 nm in diameter. The fluorescence intensity and lifetime of 4-loaded PIC were significantly enhanced by the incorporation 4 into PIC nanocarrier. The time-dependent intracellular uptake amount and in vitro photodynamic photocytotoxicity of the 4 within the nanocarrier were drastically improved compared with the free 4.     

Synthesis and characterization of Y-shape electron donor–acceptor type organic dyes for dye-sensitized solar cells

Three Y-shape organic dyes, (Z)-3-(5-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)thiophen-2-yl)-2-cyanoacrylic acid (OD-1), (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-2,2′-bithiophen-5-yl)-2-cyanoacrylic acid (OD-2) and (Z)-3-(5′-(3,5-bis(4-(9H-carbazol-9-yl)styryl)-4-methoxyphenyl)-3,4′-4″-trithiophenyl-5-yl)-2-cyanoacrylic acid (OD-3) were synthesized and used as sensitizers in nanocrystalline dye-sensitized solar cells (DSSCs). The introduction of the bis(carbazolylstyryl) units as an electron donor group and oligothiophene units as a both electron donors and π-spacers increased the conjugation length of the sensitizers and thus improved their molar absorption coefficient and light harvesting efficiency. DSSCs with the configuration of SnO₂:F/TiO₂/organic dye/liquid electrolyte/Pt devices were fabricated using these OD-1, OD-2 and OD-3 as a sensitizers. Among the devices, the DSSC composed of OD-3 exhibited highest power conversion efficiency of 3.03% under AM1.5G (100 mW cm⁻²).     

Deposition of rod-shaped antimony sulfide thin films from single-source antimony thiosemicarbazone precursors

Antimony sulfide thin films were deposited on glass substrates by aerosol assisted chemical vapour deposition technique using single source precursors, namely, antimony(III) thiosemicarbazones, SbCl₃(L) (L = thiosemicarbazones of thiophene-2-carboxaldehyde (1) and cinnamaldehyde (2)). The deposited films were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV-visible spectroscopy in order to identify their phases, morphologies, compositions and optical properties respectively. These characterizations revealed that the films were comprised of rod-shaped particles of orthorhombic stibnite (Sb₂S₃) with a Sb:S stoichiometry of ∼ 1:1.3. The calculated optical band gap from UV-vis absorption spectrum is found to be 3.48 eV.     

Preparation and optical properties of organic/inorganic nanocomposite materials by UV curing process

In this study, photo-polymerized poly(acrylic)/silica hybrid thin films were prepared from various acrylic monomers and monodispersed colloidal silica with the coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA). The silica content in the hybrid thin films varied from 0 to 50 wt.%. The experimental results show that the particle size of silica in hybrid films could be effectively controlled at 15–20 nm as the weight ratio of MSMA to colloidal silica is higher than 0.68 and 0.60 for the poly(methyl methacrylate)/silica (US) and poly(ethylene glycol dimethacrylate-trimethylolpropane trimethacrylate)/silica (UDT) hybrid materials, respectively. The polymerization conversion for US and UDT hybrid materials could reach to 100% and 94.5%, respectively. The comparison of surface roughness with the film thickness is less than 0.10%, indicating the excellent surface planarity of the prepared hybrid thin films. Besides, the prepared hybrid films from the crosslinked acrylic polymer moiety show much better film uniformity, thermal stability and mechanical properties than those obtained from poly(methyl methacrylate). The refractive index decreases with increasing the silica content in the hybrid films. Excellent optical transparency is obtained in the prepared hybrid films. These results show that the prepared hybrid thin films have potential applications as passive films for optical devices.     

Synthesis and characterization of Cu3N-WC nanocomposite films prepared by direct current magnetron sputtering

Cu₃N-WC films were synthesized on an arc ion plated TiN_x interlayer by direct current magnetron sputtering. The Cu₃N-WC films, composed of columnar WC crystals 3-5 nm in size and amorphous Cu₃N phases, were grown using the layer-plus-island mode. Deposition rate of Cu₃N-WC films declined from 11.7 to 7.5 nm/min when the WC target power increased from 200 to 400 W because the Cu target was poisoned by the diffusion of WC molecules. Nano-indentation testing results showed that the highest measure of hardness of Cu₃N-WC films was up to ∼ 41 GPa and the H³/E^?2 value of the Cu₃N-WC_47.4 was around 0.41 GPa, indicating the excellent plastic deformation resistance of the film. Incorporation of the soft lubricant Cu₃N phase and the uniform distribution of WC hard phases resulted in significant improvements in friction coefficient and wear resistance. As such, Cu₃N-WC films have a good potential in future wear applications.     

The effects of point of substitution on the formation of manganese phthalocyanine-based molecular materials: Surface characterization and electrocatalysis

Molecular films of manganese phthalocyanine (MnPc) complexes, tetra-substituted with 2-diethylaminoethanethio at the peripheral (Mn(OAc)-β-TDEAETPc, 1) and non-peripheral (Mn(OAc)-α-TDEAETPc, 2) positions were formed on glassy carbon electrode by electropolymerization and electrodeposition respectively. Atomic force microscopy images confirmed the presence of the films and revealed significant morphological differences. The films exhibited an electrocatalytic activity towards the oxidation of the insecticide, bendiocarb. Hydrodynamic technique, using rotating disc electrode voltammetry, was used to investigate the kinetics of electro-oxidation of the insecticide. Morphological differences of the films significantly influenced kinetic parameters. Values of Tafel slopes, obtained from Tafel plots, suggested that catalysis of bendiocarb occurred via outer sphere mechanism.     

Crystal structure,nonlinear optical and photophysical properties of a novel chromophore constructed with terpyridine,triphenylamine and ethyl cyanocaetate functional moieties

A novel chromophore (Z)-ethyl-3-(4-((4-([2,2′:6′,2″-terpyridin]-4′-yl)phenyl) (phenyl) amino)phenyl)-2-cyanoacrylate(3), constructed with triphenylamine moiety as the electron donor (D), 2, 2: 6, 2-terpyridine moiety as an electron acceptor (A), and ethyl cyanocaetate group as an auxiliary electron acceptor (A′), has been designed and synthesized. The crystal structures of 3 and its mediator 2 (4″-(4′-(4-(Diphenylamino) phenyl) aldehyde)-2,2′:6′,2″-Terpyridine), have been determined by single crystal X-ray diffraction analysis. The linear and nonlinear spectra of these chromophores were investigated on the basis of experimental and calculation methods. The two-photon absorption (TPA) cross-sections of 1–3 were determined by a femtosecond open-aperture Z-scan technique. The maximum value of the TPA cross-section (σ) for 3 is 7938.3 GM in DMF solution. However, much weaker two-photon absorption responses were observed at the same condition for chromophore 1 and 2, respectively. The results of the work indicate that, the photophysical properties of the D–A configuration group are influenced largely by the auxiliary moiety (A′) attached.     

Active damping of geometrically nonlinear vibrations of doubly curved laminated composite shells

This paper deals with the analysis of active constrained layer damping (ACLD) of geometrically nonlinear transient vibrations of doubly curved laminated composite shells. Vertically/obliquely reinforced 1–3 piezoelectric composite (PZC) and active fiber composite (AFC) materials are used as the materials of the constraining layer of theACLD treatment. The Golla–Hughes–McTavish (GHM) method has been implemented to model the constrained viscoelastic layer of the ACLD treatment in time domain. The first-order shear deformation theory (FSDT) and the Von Kármán type non-linear strain displacement relations are used for analyzing this coupled electro-elastic problem. A three dimensional finite element (FE) model of doubly curved laminated smart composite shells integrated with ACLD patches has been developed to investigate the performance of these patches for controlling the geometrically nonlinear transient vibrations of the shells. The numerical results indicate that the ACLD patches significantly improve the damping characteristics of the doubly curved laminated cross-ply and angle-ply shells for suppressing their geometrically nonlinear transient vibrations. It is found that the performance of the ACLD patch with its constraining layer being made of the AFC is significantly higher than that of the ACLD patch with vertically/obliquely reinforced 1–3 PZC constraining layer. The effects of variation of piezoelectric fiber orientation in both the obliquely reinforced 1–3 PZC and the AFC constraining layers on the control authority of the ACLD patches have also been investigated.     

Thermally and electrochemically stable amorphous hole-transporting materials based on carbazole dendrimers for electroluminescent devices

Amorphous hole-transporting carbazole dendrimers, 1,4-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-2,6-di(2-ethylhexyloxy)benzene (G2CB) and 1,4-bis[3,6-di(carbazol-9-yl)carbazol-9-yl]-9-(2-ethylhexyl)carbazole (G2CC), were synthesized by a divergent approach involving bromination and Ullmann coupling reactions. Compounds G2CB and G2CC showed high thermal stability (T_g = 206 to 245 °C) and excellent electrochemical reversibility. Double-layer organic light-emitting diodes were fabricated by using G2CB and G2CC as hole-transporting layers (HTLs) and tris(8-quinolinato)aluminum (Alq₃) as light-emissive layer with the device configuration of indium tin oxide/HTL/Alq₃/LiF:Al. Both devices exhibited bright green emission from Alq₃. The device using G2CC as HTL has the best performance with a maximum brightness of 8900 cd/m² at 14 V and a low turn-on voltage of 3.5 V.     

Anisotropy of the spectroscopy properties of the wurtz-stannite Cu2ZnGeS4 single crystals

In this study, the near band edge anisotropic optical properties of wurtz-stannite (WS) Cu₂ZnGeS₄ single crystals were characterized using polarization-dependent transmittance and electrolyte electroreflectance (EER) techniques. Single crystals of Cu₂ZnGeS₄ were grown by chemical vapor transport method using iodine as a transport agent. Analysis of absorption spectra revealed indirect allowed transitions for Cu₂ZnGeS₄ with the band gaps of 2.02 (2.07) and 2.08 (2.14) eV for E‖b and Е‖a polarization configurations at 300 (10) K. The room-temperature EER spectra in the vicinity of the direct band edge showed anisotropic transitions at around 2.38, 2.44 and 2.45 eV for E‖b, Е‖a and Е‖c polarizations, respectively. Based on the experimental observations and recent band-structure calculations a plausible band diagram near band edge of WS-Cu₂ZnGeS₄ was constructed.     

Synthesis, photophysical, electrochemical and thermal studies on carbazole-based acceptor molecules for heterojunction solar cell

Five small molecules, 3-tricyanovinyl-N-alkylcarbazoles (6-10) have been synthesized in a cost-effective way and characterized. The molecules have high thermal stability, good thin film formation ability and are also air stable. The change of alkyl chain length altered the aggregation pattern in the thin film. Their photophysical and electrochemical studies promise a compatible highest occupied molecular orbital - lowest unoccupied molecular orbital energy level to be potentially useful as good electron acceptor materials in heterojunction solar cell in combination with copper(II)phthalocyanine or poly-3-hexylthiophene (P3HT) as donor. Significant photoluminescence quenching of P3HT in P3HT:6-10 blends were observed.     

Synthesis of diketopyrrolopyrrole (DPP)-based small molecule donors containing thiophene or furan for photovoltaic applications

Two π-conjugated small molecules based on diketopyrrolopyrrole (DPP), DPP4T and DPP2F2T, were synthesized using the Suzuki coupling reaction. DPP4T and DPP2F2T contained furan and thiophene, respectively, next to a DPP core. Organic photovoltaic cells (OPVs) were fabricated using two DPP-based oligothiophenes as donors. DPP4T showed higher power conversion efficiency (PCE) (1.44%) than DPP2F2T (0.85%). The short-circuit current (J_SC) of DPP4T (4.38 mA cm⁻²) was nearly twice that of DPP2F2T (2.49 mA cm⁻²). The improved photovoltaic properties of DPP4T could be explained by the optical properties and the film morphology.     

Synthesis and properties of a new [60] fullerene-donor system containing dicyanovinyl groups

C₆₀ covalently connected with dicyanovinyl functionalized tris[4-(2-thienyl)phenyl]amine [C₆₀-TTPA(DCV)] (compound 1) has been successfully prepared and it was found to exhibit excellent solubility in common organic solvents with a broad visible-light harvest. The theoretical calculation of its molecular geometry and electronic structure indicates that the TTPA(DCV) moiety and C₆₀ part are acting as donor and acceptor respectively; By comparing with the UV-visible absorption spectra of amine 2, the slight red shift of compound 1 could explain the existence of a small portion of charge transport between the two parts; and the fluorescence spectra of compound 1 show that the intramolecular photo-induced electron transfer from the TTPA(DCV) to C₆₀ is the main pathway for the emission quenching.     

A high triplet energy phosphine oxide derivative as a host and exciton blocking material for blue phosphorescent organic light-emitting diodes

We have designed and synthesized a blue phosphorescent host material based on a phosphine oxide moiety. 2-(diphenylphosphine oxide)-9,9′-spirobifluorene (SPPO1) was compared with N,N′-dicarbazolyl-3,5-benzene (mCP) as a blue host material in blue phosphorescent organic light-emitting diodes (PHOLEDs). The SPPO1 was effective as a host for blue PHOLEDs and the SPPO1 based blue PHOLEDs showed much higher quantum efficiency than common mCP based blue PHOLEDs. A high quantum efficiency of 16.3% and a current efficiency of 31.4 cd/A were obtained in the blue PHOLED with iridium(III) bis(4,6-(di-fluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) as a blue phosphorescent dopant. In addition, SPPO1 was also effective as an exciton blocking material for the blue PHOLED.