Edge-on Structure Research Articles

Control of molecular curvature and crystallinity of quinacridone-benzoxadiazole copolymers using different π bridge for polymer solar cells

Three quinacridone-benzoxadiazole polymers containing different spacers (PQcOx-T, PQcOx-TT and PQcOx-biT) are obtained via Suzuki coupling reaction to control the energy levels and curvature of the polymer backbones. We find a structural relationship between the polymer backbone and crystallinity, especially regarding packing orientation. PQcOx-T exhibits a zigzag conformation with a dihedral angle over 25° and shows an edge-on structure in pristine film. However, PQcOx-TT exhibits a linear conformation with a dihedral angle under 7° and shows crystallized domains and oriented morphology with shoulder peaks in the UV–vis spectra of both solution and film states. Although PQcOx-biT demonstrates a linear conformation, its electron distribution of both the ground and excited-states are localized on the acceptor unit. Consequently, the intramolecular charge transfer (ICT) effect within PQcOx-biT is poor. Linear polymers prefer regular and crystalline domains in the film state and lead to more efficient organic photovoltaic (OPV) devices. PQcOx-TT possesses a PCE value of up to 3.4%. Further, when we fabricated an inverted device, the PCE increased to 3.6% because of its small surface potential between the active layer and MoO3. The polymer packing direction and crystallinity were determined by the curvature of the polymer, which suggests an enhancement in charge transport and increases Jsc. Moreover, the small difference of surface potential can possibly improve Voc, FF and PCE.

Narrow band-gap donor–acceptor copolymers based on diketopyrrolopyrrole and diphenylethene: Synthesis, characterization and application in field effect transistor

Three low band-gap diketopyrrolopyrrole based polymers with varying donor groups of furan, thiophene and phenyl were synthesized and then copolymerized with diphenylethene. We investigate the influence of different donor groups and comonomers on the band-gap and field effect transistors. The efficient synthesis of the diketopyrrolopyrrole based copolymers was clearly characterized by a variety of measurements. Two dimensional Grazing Incident X-ray Diffraction was measured to prove that furan and thiophene based copolymers have ordered edge-on structure. These copolymers exhibited strong π–π stacking and excellent hole mobilities when applied in the electric double layer field effect transistors. The high mobility of 2.36 cm2 V−1 s−1 with an on/off ratio of 103 was achieved.

Melting behavior of thin polyethylene films

Melting behavior in thin films of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) was studied by local thermal analysis (µTA). Even in the films thinner than 100 nm, the melting temperature ( Tm) was successfully observed by µTA. For LLDPE, Tm decreased as the thickness became thinner than 150 nm. For HDPE, Tm increased with decreasing thickness. Polarized infrared spectroscopy revealed that an edge-on lamellar structure formed in both cases, meaning that the crystallite orientation may not be a reason why the thickness dependence of Tm was not the same for both resins. A possible explanation is that for LLDPE the segmental mobility in the amorphous region predominates with decreasing thickness, and for HDPE the chain orientation in the region predominates with decreasing thickness.

Well-Balanced Carrier Mobilities in Ambipolar Transistors Based on Solution-Processable Low Band Gap Small Molecules

We synthesized a solution-processable low band gap small molecule, Si1TDPP-EE-COC6, for use as a semiconducting channel material in organic thin film transistors (OTFTs). The Si1TDPP-EE-COC6 is composed of electron-rich thiophene–dithienosilole–thiophene (Si1T) units and electron-deficient diketopyrrolopyrrole (DPP) and carbonyl units. SiTDPP-EE-COC6-based OTFTs with Au source/drain electrodes were fabricated, and their electrical properties were systematically investigated with increasing thermal annealing temperature. The hole and electron mobilities of as-spun Si1TDPP-EE-COC6 were 3.3 × 10–4 and 1.7 × 10–4 cm2 V–1 s–1, respectively. The carrier mobilities increased significantly upon thermal annealing at 150 °C, yielding a hole mobility of 0.003 cm2 V–1 s–1 and an electron mobility of 0.002 cm2 V–1 s–1. The performance enhancement upon thermal annealing was strongly associated with the formation of a layered edge-on structure and a reduction in the π–π intermolecular spacing. Importantly, the use of at...

Colloids of semiconducting polymers for high-performance, environment-friendly polymer field effect transistors

Considering the recent rapid growth of polymer field effect transistor (PFET) techniques and environmental pressure to avoid the use of toxic organic solvents in industrial processes, it is very important to develop colloids of semiconducting polymers in non-toxic solvents. Herein, we demonstrate the fabrication of surfactant-free, emulsion-dispersed nanoparticles of donor–acceptor copolymers. By optimizing the deposition methods of such semiconducting polymer colloids, high mobility (2.7cm2/Vs) PFETs were fabricated via environmentally benign processes. Systematic analyses on the crystalline nature of the colloid-processed films revealed that the well-developed edge-on lamella structure comparable to that of the bulk polymer, was preserved during the colloid-fabrication processes.

Impact of Alkyl Side Chains on Thin-film Transistor Performances in Phenanthrodithiophene–Isoindigo Copolymers

Abstract Organic field-effect transistor (OFET) characteristics of phenanthrodithiophene (PDT)–isoindigo (IID) copolymers with different alkyl chains (12OD and BOBO) as an active layer, and their structure–property relationships are described. The fabricated 12OD-based OFET device exhibited hole mobility of 0.16 cm2 V−1 s−1. Grazing-incidence wide-angle X-ray scattering (GIWAXS) analysis revealed that 12OD formed highly ordered edge-on structure, whereas the BOBO film showed amorphous-like structure with no obvious π-stacking crystallites. This may be attributed to a large steric hindrance of branched side chains in the BOBO polymer, which suppresses effective π–π overlaps between the adjacent polymer backbones.

A HOT MOLECULAR CIRCUMSTELLAR DISK AROUND THE MASSIVE PROTOSTAR ORION SOURCE I

We report new Atacama Large Millimeter/Submillimeter Array (ALMA) observations of a circumstellar disk around Source I in Orion KL, an archetype of massive protostar candidate. We detected two ortho-H$_{2}$O lines at 321 GHz ($10_{2,9}$-$9_{3,6}$) and 336 GHz ($\nu_{2}=1, 5_{2,3}$-$6_{1,6}$) for the first time in Source I. The latter one is in vibrationally excited state at the lower state energy of 2939 K, suggesting an evidence of hot molecular gas close to Source I. The integrated intensity map of the 321 GHz line is elongated along the bipolar outflow while the 336 GHz line map is unresolved with a beam size of 0.4\arcsec. Both of these maps show velocity gradient perpendicular to the bipolar outflow. The velocity centroid map of the 321 GHz line implies spatial and velocity structure similar to that of vibrationally-excited SiO masers tracing the root of the outflow emanating from the disk surface. In contrast, the 336 GHz line is most likely emitted from the disk midplane with a diameter of 0.2\arcsec (84 AU) as traced by a radio continuum emission and a dark lane devoid of the vibrationally-excited SiO maser emission. The observed velocity gradient and the spectral profile of the 336 GHz H$_{2}$O line can be reconciled with a model of an edge-on ring-like structure with an enclosed mass of $>$7$M_{\odot}$ and an excitation temperature of $>$3000 K. The present results provide a further evidence of hot and neutral circumstellar disk rotating around Source I with a diameter of $\sim$100 AU scale.

Polymer solar cells based on quinoxaline and dialkylthienyl substituted benzodithiophene with enhanced open circuit voltage

A poly[benzodithiophene-alt-di-2-thienyl-quinoxaline] series (PBDTDPQ-EH, PBDTDPQ-OD, and PBDTDPQ-HDT) was synthesized via Stille coupling. Deep highest occupied molecular orbital (HOMO) levels were achieved by the introduction of 2-decyl-4-hexyl-thiophen-yl (HDT) side chains. The introduction of the various side chains increased the molecular weight of the polymers, and the polymers dissolved well in common organic solvents at room temperature. The HOMO energy level (−5.20 to −5.49 eV) decreased because of the 2D conjugated structure. X-ray diffraction analysis showed that PBDTDPQ-OD had a slightly edge-on structure. In the case of PBDTDPQ-HDT, however, the structure was amorphous due to the thiophene side chain, and the extent of π stacking increased. After fabricating bulk-heterojunction-type polymer solar cells, the OPV characteristics were evaluated. The values of open-circuit voltage (Voc), short-circuit current (Jsc), fill factor, and power conversion efficiency (PCE) were 0.88 V, 7.9 mA cm−2, 45.4%, and 3.2%, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1028–1036

Synthesis, Morphology, and Field-Effect Transistor Characteristics of Crystalline Diblock Copolymers Consisted of Poly(3-hexylthiophene) and Syndiotactic Polypropylene

We report the synthesis, morphology, and the field effect transistor (FET) characteristics of the crystalline diblock copolymers of poly(3-hexylthiophene) and syndiotactic polypropylene (P3HT-b-sPP). Four diblock copolymers with various sPP block lengths, P3HT16K-b-sPP3K (P1), P3HT16K-b-sPP6K (P2), P3HT16K-b-sPP9K (P3), and P3HT16K-b-sPP14K (P4), were prepared by the click coupling of N3-capped sPP and ethynyl-capped P3HT. The stereoregular crystalline block sPP developed different types of molecular stacking structures and led the P3HT domains to pack lamellar edge-on structure with improved charge transporting characteristics, as evidenced by the grazing incidence wide-angle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The FET hole mobilities of P1–P3 thin films were 4.15 × 10–3, 4.16 × 10–2, and 3.95 × 10–3 cm2 V–1 s–1, respectively, which were up to 1 order of magnitude higher than that of the parent P3HT thin film (1.43 × 10–3 cm2 V–1 s–1). The...

3,4-Disubstituted Polyalkylthiophenes for High-Performance Thin-Film Transistors and Photovoltaics

We demonstrate that poly(3,4-dialkylterthiophenes) (P34ATs) have comparable transistor mobilities (0.17 cm(2) V(-1) s(-1)) and greater environmental stability (less degradation of on/off ratio) than regioregular poly(3-alkylthiophenes) (P3ATs). Unlike poly(3-hexylthiophene) (P3HT), P34ATs do not show a strong and distinct π-π stacking in X-ray diffraction. This suggests that a strong π-π stacking is not always necessary for high charge-carrier mobility and that other potential polymer packing motifs in addition to the edge-on structure (π-π stacking direction parallel to the substrate) can lead to a high carrier mobility. The high charge-carrier mobilities of the hexyl and octyl-substituted P34AT produce power conversion efficiencies of 4.2% in polymer:fullerene bulk heterojunction photovoltaic devices. An enhanced open-circuit voltage (0.716-0.771 eV) in P34AT solar cells relative to P3HT due to increased ionization potentials was observed.

Direct Observation of Interfacial Morphology in Poly(3-hexylthiophene) Transistors: Relationship between Grain Boundary and Field-Effect Mobility

We investigated the effects of microstructural (crystallization and molecular orientation) and morphological alternation (grain boundary) of poly(3-hexylthiophene) (P3HT) films on the field-effect mobility (μ) before (as-spun P3HT) and after (melt-crystallized P3HT) melting of P3HT films. Although grazing incidence X-ray scattering shows that melt-crystallized P3HT has a more highly ordered edge-on structure than as-spun P3HT, the melt-crystallized P3HT reveals μ = 0.003 cm2 V−1 s−1; this is an order of magnitude lower than that of as-spun P3HT (μ = 0.01 cm2 V−1 s−1). In addition, the interfacial morphologies of the bottom surfaces of P3HT films, which are attached to the gate dielectric, were investigated using a film transfer technique. The melt-crystallized P3HT at this interface consists of well-developed nanowire crystallites with well-defined grain boundaries that act as trap states, as verified by analysis of the temperature-dependence of μ. The remarkable reduction of μ in low-molecular-weight P3HT film (8 kg/mol) that results from melt-crystallization is due to the increased number of well-defined grain boundaries.

Films of Novel Mesogenic Molecules at Air−Water and Air−Solid Interfaces

Discotic molecules are known to form highly anisotropic structures at the air-water (A-W) interface. We have studied two novel ionic discotic mesogenic molecules, viz., pyridinium tethered with hexaalkoxytriphenylene with bromide counterion (Py-Tp) and imidazolium tethered with hexaalkoxytriphenylene with bromide counterion (Im-Tp) at A-W and air-solid interfaces. The monolayer phases were investigated at the A-W interface employing surface manometry and Brewster angle microscopy techniques. They indicate a uniform monolayer phase which shows negligible hysteresis on expanding and compressing. Also, in both the systems the collapsed state completely reverts to the monolayer state. These monolayer films transferred at different surface pressures by Langmuir-Blodgett technique were studied by employing atomic force microscopy. The topographies of these films transferred at the low and high surface pressure region of the isotherm indicate a transformation of the monolayer from face-on to edge-on structure.

SMA imaging of the masers in MWC349A

AbstractIn September 2004 and September 2005 we used the Submillimeter Array (SMA) to map the distribution of hydrogen recombination line (HRL) maser spots that originate in the envelope of the peculiar star MWC349A. We measured positions in the line over a 100 km/s velocity range with 1 km/s spectral resolution. Relative angular position was estimated to an accuracy of about 0.01 arcseconds. The H30α maser components can be tracked continuously in frequency between the red- and blue-shifted peaks of the spectrum. The masers appear to trace a nearly edge-on disk-like structure. The position-velocity relationship is quite remarkable, and reminiscent of that of NCG4258. However, the “wings” in the PV relation are too steep for a simple Keplerian prescription to be correct. We present our data, and suggest a simple model to account for the steep wings.

Detailed comparison of the structures and kinematics of simulated and observed barred galaxies

We examine the observable properties of simulated barred galaxies including radial mass profiles, edge-on structure and kinematics, bar lengths and pattern speed evolution for detailed comparison to real systems. We have run several simulations in which bars are created through inherent instabilities in self-consistent simulations of a realistic disc+halo galaxy model with a disc-dominated, flat rotation curve. These simulations were run at high (N=20M particles) and low (N=500K) resolution to test numerical convergence. We determine the pattern speeds in simulations directly from the phase angle of the bar versus time and the Tremaine-Weinberg method. Fundamental dynamics do not change between the high and low resolution, suggesting that convergence has been reached in this case. We find the higher resolution is needed to simulate structural and kinematic properties accurately. The edge-on view of the higher-resolution system clearly shows the bending instability and formation of a peanut-shaped bulge. We determined bar lengths by different means to determine the simulated bar is fast, with a corotation to bar length ratio under 1.5. Simulated bars in these models form with pattern speeds slower than those observed and slow down during their evolution. Dynamical friction between the bar and dark halo is responsible for this deceleration, as revealed by the transfer of angular momentum between the disc and the halo. However, even though the pattern speed is reduced at later times, the instantaneous scale length of the disc has grown sufficiently for the bar motion to agree with many observations. By using a different model and simulation technique than other authors, we are able to compare the robustness of these methods.

Structural control in thin layers of poly(p-phenyleneethynylene)s: photophysical studies of Langmuir and Langmuir-Blodgett films.

We present the relationship between the spatial arrangement and the photophysical properties of fluorescent polymers in thin films with controlled structures. Eight surfactant poly(p-phenyleneethynylene)s were designed and studied. These detailed studies of the behavior of the polymers at the air-water interface, and of the photophysical properties of their transferred LB films, revealed key structure-property relationships. Some of the polymers displayed pi-aggregates that are characteristic of an edge-on structure at the air-water interface. Monolayer LB films of these polymers showed greatly reduced quantum yields relative to solution values. Other polymers exhibited a highly emissive face-on structure at the air-water interface, and did not form pi-aggregates. The combination of pressure-area isotherms and the surface pressure dependent in situ UV-vis spectra of the polymers at the air-water interface revealed different behavioral details. In addition, the UV-vis spectra, fluorescence spectra, and quantum yields of the LB films provide design principles for making highly emissive films.

Synthesis and Surface Chemistry Study of a New Amphiphilic PAMAM Dendrimer

A new disk-shaped amphiphilic dendrimer has been synthesized by attaching sixty-four 12-hydroxydodecanoic acid chains to a fourth generation poly(amido amine) (PAMAM) dendrimer core. Surface pressure and surface potential−area isotherm measurements have shown that the dendrimer forms a stable monolayer at the air/water interface with limiting molecular area of 160 Å2/molecule. This small area relative to the huge size of the dendrimer suggests that the dendrimer molecules form an edge-on disk-shaped structure at the air/water interface. The topography of the dendrimer monolayer was observed by Brewster angle microscopy (BAM) at air/water interface as well as by environmental scanning electron microscopy (ESEM) as a Langmuir−Blodgett film. The striplike monolayer domains observed from BAM images correspond to the monolayer topography as observed from ESEM images.

A Conformational Phase Transition in a Langmuir Film of an Amphiphilic Azacrown

We have used grazing-incidence X-ray diffraction, X-ray reflectivity, and Brewster-angle microscopy to study an amphiphilic azacrown derivative at the air−water interface. The compound studied has a ring-shaped, flexible core with six alkyl chains attached. As the density is increased, the molecules undergo a phase transition from a face-on structure, with the alkyl tails extending away from the interface, to a thicker edge-on structure, with the tails extending radially away from the core. Concomitant with this rearrangement, the film develops long-range in-plane structural order.

Comparison of adsorption characteristics of methyl orange and α-naphthol orange molecules onto the cationic Langmuir-Blodgett films

The adsorbability of dicationic Langmuir-Blodgett (LB) film, which was fabricated by film materials of N,N′-ω-p-xylylenebis(stearyldimethylammonium chloride) (XSAC), have been investigated by using dye molecules such as methyl orange (MO) and α-naphthol orange (NO) as adsorbates. The structural characterizations of these LB films before and after dye adsorption were also carried out by applying spectroscopic methods and X-ray diffraction analysis. As a result, it was found that dye molecules in the dye-adsorbed XSAC LB film exhibited the remarkable distinction in the adsorbing state, i.e., an edge-on structure for the MO molecule and a lie-flat structure for the NO molecule. Such molecular arrangements were almost the same as those of corresponding XSAC-dye complexed LB films, which was deposited from XSAC monolayers on the aqueous dye solutions. Furthermore, the dye adsorption of MO and/or NO occurred with the nearly stoichiometrical ratio of XSAC to dye in XSAC LB films, similar to the case of tristearylmethylammonium chloride (TSAC) to dye in TSAC LB films.