Linear- and angular-shaped naphthodithiophenes: selective synthesis, properties, and application to organic field-effect transistors

A straightforward synthetic approach that exploits linear- and angular-shaped naphthodithiophenes (NDTs) being potential as new core structures for organic semiconductors is described. The newly established synthetic procedure involves two important steps; one is the chemoselective Sonogashira coupling reaction on the trifluoromethanesulfonyloxy site over the bromine site enabling selective formation of o-bromoethynylbenzene substructures on the naphthalene core, and the other is a facile ring closing reaction of fused-thiophene rings from the o-bromoethynylbenzene substructures. As a result, three isomeric NDTs, naphtho[2,3-b:6,7-b']dithiophene, naphtho[2,3-b:7,6-b']dithiophenes, and naphtho[2,1-b:6,5-b']dithiophene, are selectively synthesized. Electrochemical and optical measurements of the parent NDTs indicated that the shape of the molecules plays an important role in determining the electronic structure of the compounds; the linear-shaped NDTs formally isoelectronic with naphthacene have lower oxidation potentials and more red-shifted absorption bands than those of the angular-shaped NDTs isoelectronic with chrysene. On the contrary, the performance of the thin-film-based field-effect transistors (FETs) using the dioctyl or diphenyl derivatives were much influenced by the symmetry of the molecules; centrosymmetric derivatives tend to give higher mobility (up to 1.5 cm(2) V(-1) s(-1)) than axisymmetric ones (～0.06 cm(2) V(-1) s(-1)), implying that the intermolecular orbital overlap in the solid state is influenced by the symmetry of the molecules. These results indicate that the present NDT cores, in particular the linear-shaped, centrosymmetric naphtho[2,3-b:6,7-b']dithiophene, are promising building blocks for the development of organic semiconducting materials.     

A "zig-zag" naphthodithiophene core for increased efficiency in solution-processed small molecule solar cells

A solution-processed small molecule utilizing a novel 4,9-bis(2-ethylhexyloxy)naphtho[1,2-b:5,6-b']dithiophene "zig-zag" core (zNDT) exhibits high hole mobility, upshifted frontier MO energies, and enhanced photovoltaic cell short-circuit currents, fill-factors, and power conversion efficiencies (4.7%) versus the linear NDT isomer.     

A naphthodithiophene-diketopyrrolopyrrole donor molecule for efficient solution-processed solar cells

We report the synthesis, characterization, and first implementation of a naphtho[2,3-b:6,7-b']dithiophene (NDT)-based donor molecule in highly efficient organic photovoltaics (OPVs). When NDT(TDPP)(2) (TDPP = thiophene-capped diketopyrrolopyrrole) is combined with the electron acceptor PC(61)BM, a power conversion efficiency (PCE) of 4.06 ± 0.06% is achieved-a record for a PC(61)BM-based small-molecule OPV. The substantial PCE is attributed to the broad, high oscillator strength visible absorption, the ordered molecular packing, and an exceptional hole mobility of NDT(TDPP)(2).     

苯-噻吩低聚物电子结构及载流子传输性质的理论研究

采用密度泛函理论(DFT)的B3LYP/6-31G(d)方法对以低聚噻吩为端基、 苯并二噻吩(TPT)和并三噻吩(TTT)为共轭桥、 炔键为连接臂的20个模型化合物进行了计算研究. 在优化中性与离子态几何构型基础上, 获得了前线轨道能级、 电离能(IPs)、 电子亲和势(EAs)、 空穴/电子重组能(λ_h/λ_e)、 载流子迁移率(μ_h/μ_e)及吸收光谱等信息. 结果表明, 炔键的引入及端基低聚噻吩的增加对LUMO能级的调控作用较为显著, 而共轭桥的类型对HOMO能级影响较大; 合理选择端基、 共轭桥和连接臂等结构单元可对该类材料吸光波段及强度进行有效调节. 一维电荷传输模型结果表明, 所设计的化合物均是潜在的双极性有机半导体材料, 其中2,7-二([2,2':5',2'-三噻吩]-5-基)苯并[1,2-b:6,5-b']二噻吩(A3)和2,7-二(二噻吩并噻吩-2-基乙炔基)苯并[1,2-b:6,5-b']二噻吩(a-3)具有较高的电子迁移率, 值得进一步的实验探索研究.     

Synthesis,characterization, and organic field‐effect transistors study of conjugated D–A copolymers based on dialkylated naphtho[1,2‐b:5,6‐b′]dithiophene/naphtho[1,2‐b:5,6‐b′]difuran and benzodiathiazole/benzoxadiazole

In this report, four donor–acceptor copolymers, P(NDT3‐BT), P(NDT3‐BO), P(NDF3‐BT), and P(NDF3‐BO), using 5,10‐didodecyl‐naphtho[1,2‐b:5,6‐b′]dithiophene (NDT3) or 5,10‐didodecyl‐naphtho[1,2‐b:5,6‐b′]difuran (NDF3) as an electron‐rich unit and benzodiathiazole (BT) or benzoxadiazole (BO) as an electron‐deficient one, were designed, synthesized, and characterized. Detailed systematical investigation was developed for studying the effect of the S/O atoms on the optical, electrochemical, and morphological properties of the polymers, as well as the subsequent performance of the organic field‐effect transistors (OFETs) fabricated from these copolymers. It was found that, compared with NDF3‐based P(NDF3‐BT)/P(NDF3‐BO), by replacing NDF3 with stronger aromatic NDT3, the resultant P(NDT3‐BT)/P(NDT3‐BO) show smaller lamellar distance with an increased surface roughness in solid state, and relatively higher hole mobilities are obtained. The hole mobilities of the four polymers based on OFETs varied from 0.20 to 0.32 cm² V^?1 s^?1 depending on their molecular structures, giving some valuable insights for the further design and development of a new generation of semiconducting materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2465–2476     

Molecular Stacking and Aggregation Optimization of Photoactive Layer through Solid Additive Enables High-Performance Organic Solar Cells

Regulating molecular packing and aggregation of photoactive layer is a critical but challenging issue in developing high-performance organic solar cells. Herein, two structurally similar analogues of anthra[2,3-b : 6,7-b′]dithiophene (ADT) and naphtho[1,2-b : 5,6-b′]dithiophene (NDT) are developed as solid additive to exploit their effect in regulating the molecular aggregation and π-stacking of photoactive layer. We clarify that the perpendicular arrangements of NDT can enlarge the molecular packing space and improve the face-on stacking of Y6 during the film formation, favoring a more compact and ordered long-range π-π stacking in the out-of-plane direction after the removal of NDT under thermal annealing. The edge-to-face stacked herringbone-arrangement of ADT along with its non-volatilization under thermal annealing can induce the coexistence of face-on and edge-on stacking of blend film. As a result, the NDT treatment shows encouraging effect in improving the photovoltaic performance of devices based on various systems. Particularly, a remarkable PCE of 18.85 % is achieved in the PM6 : L8-BO-based device treated by NDT additive, which is a significant improvement with regard to the PCE of 16.41 % for the control device. This work offers a promising strategy to regulate the molecular packing and aggregation of photoactive layer towards significantly improved performance and stability of organic solar cells.     

Naphtho[2,1-b:6,5-b']difuran: a versatile motif available for solution-processed single-crystal organic field-effect transistors with high hole mobility

We here report naphtho[2,1-b:6,5-b']difuran derivatives as new p-type semiconductors that achieve hole mobilities of up to 3.6 cm(2) V(-1) s(-1) along with high I(on)/I(off) ratios in solution-processed single-crystal organic field-effect transistors. These features originate from the dense crystal packing and the resulting large intermolecular π-orbital overlap as well as from the small reorganization energy, all of which originate from the small radius of an oxygen atom.     

A-π-D-π-A small-molecule donors with different end alkyl chains obtain different morphologies in organic solar cells

The small molecular donors with different end alkyl chains provide appropriate phase separation and molecular stacking orientation for all-small-molecule solar cells. The power conversion efficiency (PCE) have been improved obviously, and the highest PCE reaches 7.06%. The results demonstrate that the optimized end alkyl chains can be used to design A-π-D-π-A backbone structure small molecular electron donors for small-molecule organic solar cells.     

Development of naphtho[1,2-b:5,6-b']dithiophene based novel small molecules for efficient bulk-heterojunction organic solar cells

Two new small molecules with a rigid planar naphtho[1,2-b:5,6-b']dithiophene (NDT) unit were designed and synthesized. Solution processed bulk-hetereojunction organic solar cells based on blends of the small molecules and [6,6]-phenyl-C(71)-butyric acid methyl ester (PC(71)BM) exhibited promising photovoltaic device performance with a maximum power conversion efficiency up to 2.20% under the illumination of AM 1.5G, 100 mW cm(-2).     

Angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-difuran: are they isoelectronic with chrysene?

Although angular-shaped naphthodifurans, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-difuran, are formally isoelectronic with chrysene as their thiophene counterparts, naphtho[1,2-b;5,6-b']- and naphtho[2,1-b;6,5-b']-dithiophene, the HOMO energy level of naphthodifurans is much higher than those of naphthodithiophenes and chrysene. The difference in electronic structure in the ground state can be explained by distinct electronic perturbation from the outermost aromatic rings.     

Naphtho[2,1‐b:3,4‐b′]dithiophene‐based Bulk Heterojunction Solar Cells: How Molecular Structure Influences Nanoscale Morphology and Photovoltaic Properties

Organic bulk heterojunction photovoltaic devices based on a series of three naphtho[2,1‐b:3,4‐b′]dithiophene (NDT) derivatives blended with phenyl‐C₇₁‐butyric acid methyl ester were studied. These three derivatives, which have NDT units with various thiophene‐chain lengths, were employed as the donor polymers. The influence of their molecular structures on the correlation between their solar‐cell performances and their degree of crystallization was assessed. The grazing‐incidence angle X‐ray diffraction and atomic force microscopy results showed that the three derivatives exhibit three distinct nanoscale morphologies. We correlated these morphologies with the device physics by determining the J–V characteristics and the hole and electron mobilities of the devices. On the basis of our results, we propose new rules for the design of future generations of NDT‐based polymers for use in bulk heterojunction solar cells.     

Effect of backbone structures on photovoltaic properties in naphthodithiophene‐based copolymers

A “zigzag” naphthodithiophene‐based copolymer, poly[4,9‐bis(2‐ethylhexyloxy)naphtho[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl‐alt‐1,3‐(5‐heptadecan‐9‐yl)‐4H‐thieno[3,4‐c]pyrrole‐4,6‐dione] (P1) is synthesized and its properties are compared to “linear” naphthodithiophene‐based copolymer, poly[4,9‐bis(2‐ethylhexyloxy)naphtho[2,3‐b:6,7‐d′]dithiophene‐2,7‐diyl‐alt‐1,3‐(5‐heptadecan‐9‐yl)‐4H‐thieno[3,4‐c]pyrrole‐4,6‐dione] (P2). The field‐effect carrier mobilities and the optical, electrochemical, and photovoltaic properties of the copolymers are systematically investigated. The results suggest that the backbone of the copolymer structure significantly influences the band gap, electronic energy levels, carrier mobilities, and photovoltaic properties of the resultant thin films. In this work, the zigzag naphtho[1,2‐b:5,6‐b′]dithiophene‐based copolymer displays a good hole mobility and a high open‐circuit voltage; however, polymer solar cells in which the linear naphtho[2,3‐b;6,7‐d′]dithiophene‐based copolymer is used as the electron donor material perform better than the cells prepared using the zigzag naphtho[1,2‐b:5,6‐b′]dithiophene‐based copolymer. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 305–312     

Stable polythiophene semiconductors incorporating thieno[2,3-b]thiophene

This work describes a new design methodology that allows the preparation of air stable, semiconducting thiophene polymers with high charge carrier mobilities. The incorporation of thieno[2,3-b]thiophene into a polythiophene backbone introduces cross-conjugated double bonds that disfavor full delocalization, leading to high ionization potential in comparison to a fully conjugated polythiophene, with no reduction in charge carrier mobility. The resulting solution processable polymers exhibit charge carrier mobilities up to 0.15 cm2/V s and on/off ratios greater than 105 when measured in air. Transistors exhibit lifetimes of several months in air with no encapsulation necessary.     

Lewis acid adducts of narrow band gap conjugated polymers

We report on the interaction of Lewis acids with narrow band gap conjugated copolymers containing donor and acceptor units. Examination of the widely used poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b']dithiophene)-2,6-(diyl-alt-benzo[2,1,3]thiadiazole)-4,7-diyl] (1) shows weaker binding with B(C(6)F(5))(3) when compared with a small molecule that contains a cyclopenta-[2,1-b:3,4-b']dithiophene (CDT) unit flanked by two benzo[2,1,3]thiadiazole (BT) fragments. Studies on model compounds representative of 1, together with a comparison between B(C(6)F(5))(3) and BBr(3), indicate that the propensity for Lewis acid coordination is decreased because of steric encumbrance surrounding the BT nitrogen sites. These observations led to the design of chromophores that incorporate an acceptor unit with a more basic nitrogen site, namely pyridal[2,1,3]thiadiazole (PT). That this strategy leads to a stronger B-N interaction was demonstrated through the examination of the reaction of B(C(6)F(5))(3) with two small molecules bis(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-4,7-pyridal[2,1,3]thiadiazole (8) and bis{2-thienyl-(4,4-bis(hexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)}-4,7-pyridal[2,1,3]thiadiazole (9) and two polymer systems (poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b']dithiophene)-2,6-diyl-alt-([1,2,5]thiadiazolo[3,4-c]pyridine)-4,7-diyl] (10) and poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b']dithiophene)-2,6-diyl-alt-(4',7'-bis(2-thienyl)-[1,2,5]thiadiazolo[3,4-c]pyridine)-5,5-diyl] (11). From a materials perspective, it is worth pointing out that through the binding of B(C(6)F(5))(3), new NIR-absorbing polymers can be generated with band gaps from 1.31 to 0.89 eV. A combination of studies involving ultraviolet photoemission spectroscopy and density functional theory shows that the narrowing of the band gap upon borane coordination to the pyridal nitrogen on PT is a result of lowering the energies of both the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the optically relevant fragments; however, the LUMO is decreased to a greater extent, thereby giving rise to the narrowing of the gap.     

新型芳并吡喃类多环化合物的合成与光谱性质研究

本文设计并经由分子内碳-碳偶联反应合成了一系列基于芳并吡喃供电子功能片段的有机功能小分子,包括萘并[2,1-b：6,5-b’]二苯并吡喃4a,萘并[2,1-b：6,5-b’]二萘并吡喃4b,萘并[2,1-b：6,5-b’]二[2-（5-己基噻吩基）]苯并吡喃4c。通过紫外光谱和荧光光谱研究表明,这类化合物在370~400 nm波长范围内具有最大紫外吸收,在417~462 nm波长范围内具有最大荧光发射。说明随着共轭平面的增大或共轭链长度的增加,化合物的吸收和荧光光谱均发生显著的红移,是一类具有丰富光电活性的有机功能分子。     

Synthesis, solid state structure and polymerisation of a fully planar cyclopentadithiophene

The new fully planar cyclopentadithiophene, 4-n-dodecylidene-4H-cyclopenta(2,1-b;3,4-b')dithiophene, shows extensive pi-stacking in the solid state with short intermolecular distances (ca. 3.5 A) between adjacent molecules. Polymerisation of this monomer by two different protocols gave solution processable alkenyl-bridged cyclopentadithiophene polymers with extended pi-conjugation in the main chain.     

Organic dyes incorporating the benzo[1,2-b:4,5-b']dithiophene moiety for efficient dye-sensitized solar cells

A new class of organic sensitizers incorporating a benzo[1,2-b:4,5-b']dithiophene (BDT) unit as conjugated spacer has been synthesized and successfully used for dye-sensitized solar cells (DSSCs). The length of the π-conjugated spacers has a strong impact on electro-optical properties of these dyes, leading to the conversion efficiencies ranging from 4.17 to 5.68% under AM 1.5 G irradiation. This result indicates that the BDT unit is a promising candidate in organic sensitizers.     

Synthesis and properties of thiophene-fused benzocarborane

The o-carborane-based π-conjugated compound, benzocarborano- [2,1-b:3,4-b']dithiophene was synthesized. Its crystal structure revealed high coplanarity for the two thiophene rings of the 2,2'-bithiophene skeleton, which is fixed in the cisoid structure by the o-carborane unit. Theoretical calculations indicated non-aromaticity for its center C(6) ring moiety as well as decreased HOMO and LUMO levels. The o-carborane moiety provides an electron-withdrawing character to the 2,2'-bithiophene unit through an inductive effect.     

Naphthodithiophene-based donor materials for solution processed organic solar cells

As an emerging donor building block, naphthodithiophene (NDT) is causing more concerns in the field of organic semiconductors. With the rigid and coplanar molecule structure, NDT will exhibit more application space relying on its own advantage for facilitating the charge carrier transport. In this review article, we have summarized the development progress on the NDT-based donor materials for solution processed organic solar cells. Discussions and comments on those representative NDT type materials about structure and property are also presented.     

O-Doped Nanographenes: A Pyrano/Pyrylium Route Towards Semiconducting Cationic Mixed-Valence Complexes

Herein we report an efficient synthesis to prepare O-doped nanographenes derived from the π-extension of pyrene. The derivatives are highly fluorescent and feature low oxidation potentials. Using electrooxidation, crystals of cationic mixed-valence (MV) complexes were grown in which the organic salts organize into face-to-face π-stacks, a favorable solid-state arrangement for organic electronics. Variable-temperature electron paramagnetic resonance (EPR) measurements and relaxation studies suggest a strong electron delocalization along the longitudinal axis of the columnar π-stacking architectures. Electric measurements of single crystals of the MV salts show a semiconducting behavior with a remarkably high conductivity at room temperature. These findings support the notion that π-extension of heteroatom-doped polycyclic aromatic hydrocarbons is an attractive approach to fabricate nanographenes with a broad spectrum of semiconducting properties and high charge mobilities.