Material design and synthesis of heteroarene-based organic semiconductors for organic transistors and solar cells

Conferencia sobre los recientes avances en el diseño de moléculas orgánica para dispositivos fotovoltaicosThe filed of organic electronics has emerged as a potential technology enabling to realize low cost, ubiquitous, and soft electronics applications. One of the key materials in the technology is organic semiconductors that act as the active material in the electronic devices such as organic field-effect transistors (OFETs) and organic photovoltaic cells (OPVs). Our research group in Hiroshima University has tried to contribute to the developments of organic semiconductors including small molecular- and conjugated polymer-based materials. In particular, we have focused on fused-heterarene structures as the key building unit. Such heteroarenes are [1]benzothieno[3,2-b][1]benzothiophene (BTBT) [1], dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) [2], dianthra[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DATT) [3], isomeric naphthodithiophenes (NDTs) [4], anthra[2,3-b;6,7-b’]dichalcogenophenes (ADXs) [5], benzo[1,2-b;4,5-b’]dichalcogenophenes (BDXs) [6], naphtho[1,2-c:5,6-c’]bis[1,2,5]thiadiazole (NTz) [7], naphthodithiophene diimide (NDTI) [8] (Fig. 1). These heteroarenes can be efficiently synthesized and modified to afford superior molecular semiconductors, or incorporated into conjugated chains to provide new semiconducting polymers. In this presentation, synthetic chemistry and design strategy of these materials are discussed together with their device characteristics.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Transient nature of graphene quantum dot formation via a hydrothermal reaction

A facile, economic and environmentally friendly one-step approach for the preparation of highly luminescent graphene quantum dots (GQDs) was developed using a hydrothermal reaction between citric acid and urea. Unlike previous reports, we focused on the effect of the transient nature of GQD formation on the photoluminescence (PL) properties and molecular structure changes of the products. We found that the GQDs have an optimum reaction time and require an effective precursor to achieve excellent luminescent properties. The PL, ultraviolet-visible (UV-vis) absorption, zeta potential, and nuclear magnetic resonance (NMR) analyses of the GQDs prepared at various reaction times revealed that the molecular structures responsible for the luminescence of the GQDs are aggregates or condensation products of citric acid amides. We found that urea addition to the precursor drastically enhances the PL intensity of the GQDs, and it is 40 times higher than those prepared using the pure citric acid precursor. Additionally, a GQDs–polyvinyl alcohol composite achieved an excellent quantum yield (QY) of 43.6%.This work was supported by JSPS KAKENHI Grant numbers 26709061 and 24656413. We thank Dr Eishi Tanabe from the Hiroshima Prefectural Institute of Industrial Science and Technology for helping with TEM analyses, and Drs Naoya Tochio and Junichi Kakimura from Hiroshima University for NMR analyses

Raman Activities of Cyano-Ester Quinoidal Oligothiophenes Reveal Their Diradical Character and the Proximity of the Low-Lying Double Exciton State

Quinoidal oligothiophenes have received considerable attention as interesting platforms with remarkable amphoteric redox behavior associated with their diradical character increasing with the conjugation lengths. In this work, we considered a family of quinoidal oligothiophenes bearing cyano-ester terminal groups and characterized them by UV-Vis-NIR absorption and Raman spectroscopy measurements at different excitation wavelengths. The experimental investigation is complemented by quantum-chemical studies to assess the quality of computed density functional theory (DFT) ground state structures and their influence on predicted Raman intensities. In addition, resonance conditions with the optically active HOMO→LUMO transition as well as with the more elusive state dominated by the doubly excited HOMO,HOMO→LUMO,LUMO configuration, are determined with DFT-MRCI calculations and their contributions to Raman activity enhancement are discussed in terms of computed vibrational Huang–Rhys (HR) factorsWe thank MINECO/FEDER of the Spanish Government (project reference PGC2018-098533-B-100) and the Junta de Andalucía, Spain (UMA18FEDERJA057). Partial funding for open access charge: Universidad de Málag

J.Mater.Chem.C

Correction for ‘“Heavy-atom effects” in the parent [1]benzochalcogenopheno[3,2-b][1]benzochalcogenophene system’ by Chengyuan Wang et al., J. Mater. Chem. C, 2020, 8, 15119–15127, DOI: https://doi.org/10.1039/D0TC01408G

Chasing the ‘Killer’ Phonon Mode for the Rational Design of Low Disorder, High Mobility Molecular Semiconductors

Molecular vibrations play a critical role in the charge transport properties of weakly van der Waals bonded organic semiconductors. To understand which specific phonon modes contribute most strongly to the electron – phonon coupling and ensuing thermal energetic disorder in some of the most widely studied high mobility molecular semiconductors, we have combined state-of-the-art quantum mechanical simulations of the vibrational modes and the ensuing electron phonon coupling constants with experimental measurements of the low-frequency vibrations using inelastic neutron scattering and terahertz time-domain spectroscopy. In this way we have been able to identify the long-axis sliding motion as a ‘killer’ phonon mode, which in some molecules contributes more than 80% to the total thermal disorder. Based on this insight, we propose a way to rationalize mobility trends between different materials and derive important molecular design guidelines for new high mobility molecular semiconductors.Royal Society German Research Foundation European Research Council Engineering and Physical Sciences Research Council ARCHER UK National Supercomputing Service Belgian National Fund for Scientific Research Leverhulme Trust Wiener-Anspach Foundation Belgian Walloon Region GENCI-CINES/IDRI

Strong Suppression of Thermal Conductivity in the Presence of Long Terminal Alkyl Chains in Low‐Disorder Molecular Semiconductors

Funder: Consortium des Équipements de Calcul IntensifFunder: The Leverhulme TrustAbstract: While the charge transport properties of organic semiconductors have been extensively studied over the recent years, the field of organics‐based thermoelectrics is still limited by a lack of experimental data on thermal transport and of understanding of the associated structure–property relationships. To fill this gap, a comprehensive experimental and theoretical investigation of the lattice thermal conductivity in polycrystalline thin films of dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (Cn‐DNTT‐Cn with n = 0, 8) semiconductors is reported. Strikingly, thermal conductivity appears to be much more isotropic than charge transport, which is confined to the 2D molecular layers. A direct comparison between experimental measurements (3ω–Völklein method) and theoretical estimations (approach‐to‐equilibrium molecular dynamics (AEMD) method) indicates that the in‐plane thermal conductivity is strongly reduced in the presence of the long terminal alkyl chains. This evolution can be rationalized by the strong localization of the intermolecular vibrational modes in C8‐DNTT‐C8 in comparison to unsubstituted DNTT cores, as evidenced by a vibrational mode analysis. Combined with the enhanced charge transport properties of alkylated DNTT systems, this opens the possibility to decouple electron and phonon transport in these materials, which provides great potential for enhancing the thermoelectric figure of merit ZT

新規電子供与体の設計, 合成とその物性研究

Contents General Introduction / p1 Chapter1.Syntheses and properties of dimethyl and tetramethyl anthra[1,9-cd:4,10-c'd']bis[1,2]dichalcogenoles and their charge-transfer complexes. / p11 Chapter2.Syntheses,crystal structures and properties of radical cation salts of 2,3-dimethyltetrathioanthracene(2,3-DMTTA)and 2,3-dimetyltetraselenoanthracene(2,3-DMTSA). / p38 Chapter3.Syntheses and properties of peri-dichalcogen bridged phenanthrene donors. / p54 Chapter4.Syntheses,crystal structures and physical properties of novel heteroarene donors. / p79 Chapter5.Synthses,electrochemical,and optical properties of pyranylidenemethyl-and thiopyranylidenemethyl-substituted furans,thiophenes,and N-methylpyrroles. / p95 Closing Remarks / p106 List of Publications / p108広島大学(Hiroshima University)博士(工学)Engineeringdoctora

Design strategy for air-stable organic semiconductors applicable to high-performance field-effect transistors

Electronic structure of air-stable, high-performance organic field-effect transistor (OFET) material, 2,7-dipheneyl[1]benzothieno[3,2-b]benzothiophene (DPh-BTBT), was discussed based on the molecular orbital calculations. It was suggested that the stability is originated from relatively low-lying HOMO level, despite the fact that the molecule contains highly π-extended aromatic core ([1]benzothieno[3,2-b]benzothiophene, BTBT) with four fused aromatic rings like naphthacene. This is rationalized by the consideration that the BTBT core is not isoelectronic with naphthacene but with chrysene, a cata-condensed phene with four benzene rings. It is well known that the acene-type compound is unstable among its structural isomers with the same number of benzene rings. Therefore, polycyclic aromatic compounds possessing the phene-substructure will be good candidates for stable organic semiconductors. Considering synthetic easiness, we suggest that the BTBT-substructure is the molecular structure of choice for developing air-stable organic semiconductors

Organic superconductors with an incommensurate anion structure

Superconducting incommensurate organic composite crystals based on the methylenedithio-tetraselenafulvalene (MDT-TSF) series donors, where the energy band filling deviates from the usual 3/4-filled, are reviewed. The incommensurate anion potential reconstructs the Fermi surface for both (MDT-TSF)(AuI2)0.436 and (MDT-ST)(I3)0.417 neither by the fundamental anion periodicity q nor by 2q, but by 3q, where MDT-ST is 5H-2-(1,3-dithiol-2-ylidene)-1,3-diselena-4,6-dithiapentalene, and q is the reciprocal lattice vector of the anion lattice. The selection rule of the reconstructing vectors is associated with the magnitude of the incommensurate potential. The considerably large interlayer transfer integral and three-dimensional superconducting properties are due to the direct donor–donor interactions coming from the characteristic corrugated conducting sheet structure. The materials with high superconducting transition temperature, Tc, have large ratios of the observed cyclotron masses to the bare ones, which indicates that the strength of the many-body effect is the major determinant of Tc. (MDT-TS)(AuI2)0.441 shows a metal–insulator transition at TMI=50 K, where MDT-TS is 5H-2-(1,3-diselenol-2-ylidene)-1,3,4,6-tetrathiapentalene, and the insulating phase is an antiferromagnet with a high Néel temperature (TN=50 K) and a high spin–flop field (Bsf=6.9 T). There is a possibility that this material is an incommensurate Mott insulator. Hydrostatic pressure suppresses the insulating state and induces superconductivity at Tc=3.2 K above 1.05 GPa, where Tc rises to the maximum, Tcmax=4.9 K at 1.27 GPa. This compound shows a usual temperature–pressure phase diagram, in which the superconducting phase borders on the antiferromagnetic insulating phase, despite the unusual band filling