Hybrid Energy-Minimization Simulation of Equilibrium Droplet Shapes on Hydrophilic/Hydrophobic Patterned Surfaces

We have developed an efficient algorithm for simulating the equilibrium shape of a microdroplet placed on a flat substrate that has a fine, discontinuous, and arbitrarily shaped hydrophilic/hydrophobic patterned surface. The method uses a hybrid energy-minimization technique that combines the direct search method to determine the droplet shape around solid/liquid contact lines with the gradient descent method for the other parts of the droplet surface. The method provides high-convergence at a low computational cost with sufficient mesh resolution, providing a useful tool for the optimal design of printed electronic devices

Correlated Proton Transfer and Ferroelectricity along Alternating Zwitterionic and Nonzwitterionic Anthranilic Acid Molecules

Correlated Proton Transfer and Ferroelectricity along Alternating Zwitterionic and Nonzwitterionic Anthranilic Acid Molecule

Fundamenta Botanica Tom. VII

Here, we investigated photocarrier generation and diffusion characteristics in molecular-scale donor–acceptor charge-transfer (CT) systems. The photocarrier diffusion characteristics were measured on a series of mixed-stack CT compound crystals by the laser beam-induced current (LBIC) technique where the photocurrent is detected on the crystal surfaces as a function of either the laser illuminated position or the laser-modulation frequency. In the compounds with CT gap energy larger than 0.7 eV, the diffusion length of photocarriers reached larger than 10 μm. The dependence of diffusion length on the electric field and the laser-modulated frequency clearly indicates the direct generation of long-lived photocarriers without forming exciton. In contrast, the photocarrier diffusion was suppressed, and the diffusion length got smaller than 2 μm in the compounds with a gap energy smaller than 0.7 eV. We discuss that the electron–hole recombination becomes dominated when the CT gap energy is as small as the molecular reorganization energy. The results suggest that proper choice of donor–acceptor combination should promote efficient charge separation in organic photovoltaic cells (OPCs)

Enhanced Layered-Herringbone Packing due to Long Alkyl Chain Substitution in Solution-Processable Organic Semiconductors

Herein, we report the stabilization and modulation of <i>layered-herringbone</i> (LHB) packing, which is known to afford high-performance organic thin-film transistors, based on crystal structure analyses and calculations of intermolecular interaction energies for alkyl-substituted organic semiconductor (OSC) crystals. We systematically investigated the alkyl chain-length dependence of the crystal structures, solvent solubilities, and thermal characteristics for three series of symmetrically and asymmetrically alkyl-substituted benzothieno­[3,2-<i>b</i>]­[1]­benzothiophenes (BTBTs). All the series exhibit LHB packing when the BTBTs are substituted with relatively long alkyl chains (−C_<i>n</i>H_2<i>n</i>+1), i.e., <i>n</i> ≥ 4 for monoalkylated, <i>n</i> ≥ 6 for dialkylated, and <i>n</i> ≥ 5 for phenyl-alkylated BTBTs. LHB packing is also evident in the nonsubstituted and diethyl-substituted BTBTs, although those substituted with short alkyl chains generally did not feature LHB packing because of their lack of interchain ordering. The density functional theory calculations of the intermolecular interactions revealed that the BTBT cores inherently generate LHB packing, and the stability is increasingly enhanced by the alignment of longer alkyl chains. It was also found that the LHB packing is stabilized by keeping the size ratios of the total intermolecular attractive forces between the <i>T-shaped</i> and <i>slipped parallel</i> contacts at about 3:2 for all the LHB compounds, despite the slight structural modifications generated by the substituents. We discuss the effects of alkyl substitutions to modulate the LHB packing of the BTBT cores and thus the two-dimensional carrier transport in layered OSC crystals

Extended and Modulated Thienothiophenes for Thermally Durable and Solution-Processable Organic Semiconductors

Herein, we report the rational design of practical small-molecule organic semiconductors based on a π-electron skeleton of benzothieno­[3,2-<i>b</i>]­naphtho­[2,3-<i>b</i>]­thiophene (BTNT) whose layered herringbone (LHB) packing is intentionally modulated by the designated asymmetric substitutions with the phenyl group and normal alkyl chains. The thermal stability of the hybrid BTNT core is high enough, as it lies between those of dinaphtho­[2,3-<i>b</i>:2′,3′-<i>f</i>]­thieno­[3,2-<i>b</i>]­thiophene (DNTT) and benzothieno­[3,2-<i>b</i>]­benzothiophene (BTBT), although the solvent solubility for the substituted BTNT at ordinary 2,8-substituting positions by the alkyl chain and phenyl group remains extremely low. We show in the BTBT and BTNT derivatives that the tuning of the substituting position works to slightly bend the rodlike organic semiconductor molecules and thus to decrease the cohesive energy of the crystals with retention of the bilayer-type herringbone (<i>b</i>-LHB) packing for the asymmetric rodlike molecules. This modification eventually leads to an increase in solvent solubility, a decrease in phase transition temperature, and the suppression of liquid-crystalline phases at high temperatures. By using the substituting effect, we successfully achieve the organic semiconductors with modulated alkylated Ph-BTNT that exhibits both a sufficiently high solvent solubility and a sufficiently high thermal stability. The variation in the crystal packing also enhances the intermolecular transfer integrals along the T-shaped contacts within the intralayer herringbone packing. Spin coating of the material under ambient conditions affords high-performance bottom-gate, bottom-contact organic thin-film transistors, exhibiting high thermal durability in the device characteristics below 150 °C. The obtained devices also exhibit a higher mobility, a lower threshold voltage, and a smaller subthreshold swing, by initial thermal treatment at 140 °C, composed to those of the as-prepared films, because the thermal treatment stabilizes the <i>b</i>-LHB packing and thus suppresses the residual minority holes and shallow traps. These findings should be crucial in the design and development of organic semiconductor materials for practical printed electronics applications

Extended and Modulated Thienothiophenes for Thermally Durable and Solution-Processable Organic Semiconductors

Herein, we report the rational design of practical small-molecule organic semiconductors based on a π-electron skeleton of benzothieno­[3,2-<i>b</i>]­naphtho­[2,3-<i>b</i>]­thiophene (BTNT) whose layered herringbone (LHB) packing is intentionally modulated by the designated asymmetric substitutions with the phenyl group and normal alkyl chains. The thermal stability of the hybrid BTNT core is high enough, as it lies between those of dinaphtho­[2,3-<i>b</i>:2′,3′-<i>f</i>]­thieno­[3,2-<i>b</i>]­thiophene (DNTT) and benzothieno­[3,2-<i>b</i>]­benzothiophene (BTBT), although the solvent solubility for the substituted BTNT at ordinary 2,8-substituting positions by the alkyl chain and phenyl group remains extremely low. We show in the BTBT and BTNT derivatives that the tuning of the substituting position works to slightly bend the rodlike organic semiconductor molecules and thus to decrease the cohesive energy of the crystals with retention of the bilayer-type herringbone (<i>b</i>-LHB) packing for the asymmetric rodlike molecules. This modification eventually leads to an increase in solvent solubility, a decrease in phase transition temperature, and the suppression of liquid-crystalline phases at high temperatures. By using the substituting effect, we successfully achieve the organic semiconductors with modulated alkylated Ph-BTNT that exhibits both a sufficiently high solvent solubility and a sufficiently high thermal stability. The variation in the crystal packing also enhances the intermolecular transfer integrals along the T-shaped contacts within the intralayer herringbone packing. Spin coating of the material under ambient conditions affords high-performance bottom-gate, bottom-contact organic thin-film transistors, exhibiting high thermal durability in the device characteristics below 150 °C. The obtained devices also exhibit a higher mobility, a lower threshold voltage, and a smaller subthreshold swing, by initial thermal treatment at 140 °C, composed to those of the as-prepared films, because the thermal treatment stabilizes the <i>b</i>-LHB packing and thus suppresses the residual minority holes and shallow traps. These findings should be crucial in the design and development of organic semiconductor materials for practical printed electronics applications

Extended and Modulated Thienothiophenes for Thermally Durable and Solution-Processable Organic Semiconductors

Herein, we report the rational design of practical small-molecule organic semiconductors based on a π-electron skeleton of benzothieno­[3,2-<i>b</i>]­naphtho­[2,3-<i>b</i>]­thiophene (BTNT) whose layered herringbone (LHB) packing is intentionally modulated by the designated asymmetric substitutions with the phenyl group and normal alkyl chains. The thermal stability of the hybrid BTNT core is high enough, as it lies between those of dinaphtho­[2,3-<i>b</i>:2′,3′-<i>f</i>]­thieno­[3,2-<i>b</i>]­thiophene (DNTT) and benzothieno­[3,2-<i>b</i>]­benzothiophene (BTBT), although the solvent solubility for the substituted BTNT at ordinary 2,8-substituting positions by the alkyl chain and phenyl group remains extremely low. We show in the BTBT and BTNT derivatives that the tuning of the substituting position works to slightly bend the rodlike organic semiconductor molecules and thus to decrease the cohesive energy of the crystals with retention of the bilayer-type herringbone (<i>b</i>-LHB) packing for the asymmetric rodlike molecules. This modification eventually leads to an increase in solvent solubility, a decrease in phase transition temperature, and the suppression of liquid-crystalline phases at high temperatures. By using the substituting effect, we successfully achieve the organic semiconductors with modulated alkylated Ph-BTNT that exhibits both a sufficiently high solvent solubility and a sufficiently high thermal stability. The variation in the crystal packing also enhances the intermolecular transfer integrals along the T-shaped contacts within the intralayer herringbone packing. Spin coating of the material under ambient conditions affords high-performance bottom-gate, bottom-contact organic thin-film transistors, exhibiting high thermal durability in the device characteristics below 150 °C. The obtained devices also exhibit a higher mobility, a lower threshold voltage, and a smaller subthreshold swing, by initial thermal treatment at 140 °C, composed to those of the as-prepared films, because the thermal treatment stabilizes the <i>b</i>-LHB packing and thus suppresses the residual minority holes and shallow traps. These findings should be crucial in the design and development of organic semiconductor materials for practical printed electronics applications

Extended and Modulated Thienothiophenes for Thermally Durable and Solution-Processable Organic Semiconductors

Herein, we report the rational design of practical small-molecule organic semiconductors based on a π-electron skeleton of benzothieno­[3,2-<i>b</i>]­naphtho­[2,3-<i>b</i>]­thiophene (BTNT) whose layered herringbone (LHB) packing is intentionally modulated by the designated asymmetric substitutions with the phenyl group and normal alkyl chains. The thermal stability of the hybrid BTNT core is high enough, as it lies between those of dinaphtho­[2,3-<i>b</i>:2′,3′-<i>f</i>]­thieno­[3,2-<i>b</i>]­thiophene (DNTT) and benzothieno­[3,2-<i>b</i>]­benzothiophene (BTBT), although the solvent solubility for the substituted BTNT at ordinary 2,8-substituting positions by the alkyl chain and phenyl group remains extremely low. We show in the BTBT and BTNT derivatives that the tuning of the substituting position works to slightly bend the rodlike organic semiconductor molecules and thus to decrease the cohesive energy of the crystals with retention of the bilayer-type herringbone (<i>b</i>-LHB) packing for the asymmetric rodlike molecules. This modification eventually leads to an increase in solvent solubility, a decrease in phase transition temperature, and the suppression of liquid-crystalline phases at high temperatures. By using the substituting effect, we successfully achieve the organic semiconductors with modulated alkylated Ph-BTNT that exhibits both a sufficiently high solvent solubility and a sufficiently high thermal stability. The variation in the crystal packing also enhances the intermolecular transfer integrals along the T-shaped contacts within the intralayer herringbone packing. Spin coating of the material under ambient conditions affords high-performance bottom-gate, bottom-contact organic thin-film transistors, exhibiting high thermal durability in the device characteristics below 150 °C. The obtained devices also exhibit a higher mobility, a lower threshold voltage, and a smaller subthreshold swing, by initial thermal treatment at 140 °C, composed to those of the as-prepared films, because the thermal treatment stabilizes the <i>b</i>-LHB packing and thus suppresses the residual minority holes and shallow traps. These findings should be crucial in the design and development of organic semiconductor materials for practical printed electronics applications

Effects of Substituted Alkyl Chain Length on Solution-Processable Layered Organic Semiconductor Crystals

Effects of Substituted Alkyl Chain Length on Solution-Processable Layered Organic Semiconductor Crystal