Electron-deficient Building Block Research Articles

N-Type semiconducting polymers based on an bithiophene imide-bridged isoindigo for organic field-effect transistors

n-Type polymer semiconductors are essential for enabling high-performance organic electronic devices; however, their development still remains a challenge. Herein, we reported a new electron-deficient building block, i.e. bithiophene imide (BTI)-bridged isoindigo (IID), BTIID, through a Knoevenagel condensation reaction between the bisaldehyde BTI and the alkylated indolinones. Three donor-acceptor (D-A) copolymers were then successfully synthesized via standard Stille coupling reaction based on this novel building block, which exhibit highly planar backbones and low-lying lowest unoccupied molecular orbitals (LUMO) energy levels. When integrated into organic field-effect transistors (OFETs), these polymers demonstrated unipolar n-type transport characteristics with a highest electron mobility of 5.79 × 10−4 cm2 V−1 s−1. Our research results indicate that the design of strong electron-withdrawing units via integrating two different electron-acceptor units into one single structure represents a promising strategy for developing n-type polymer semiconductors with low-lying LUMO energy levels.

Thienyl naphthodipyrrolopyrrole (TNDP)-based polymers semiconductor for n-type OFETs

Naphthodipyrrolopyrrole (NDP)-based materials as the n-type semiconductor materials are investigated, which present a good electron transport mobility. However, all the reported NDP were phenyl-substituted ones (PhNDP). Compared to the phenyl substituted chromophore, the thiophene substituted ones were often more promising due to its small size, S⋯S interaction, as well as the electron-rich behavior for the thiophene. Thus, in this work the new chromophore thiophene-substituted NDP (TNDP) was designed and synthesized for the first time via Knoevenagel reaction. In addition, two donor-acceptor typed copolymers PNDP-2T and PNDP-IDT containing TNDP were prepared. The result showed that the two polymers present not only a good aggregation and strong intramolecular charge transfer (ICT) effect, but also a low lowest unoccupied molecular orbital (LUMO) ∼ -4.17 eV. This is advantageous for the charge transport within the single molecules as well as across the neighboring polymer chains. In addition, the low LUMO energy level is beneficial for the electron injection from electrode into the semiconductor layer. As a consequence, both polymers presented n-type behavior. The electron transport mobility of PNDP-IDT was up to 0.99 cm2 V−1 s−1, which is among the highest electron mobility reported for conjugated polymers. In addition, this value is higher than the PNDP-based polymers with similar chemical structure. This work clearly shows that TNDP is an appealing electron-deficient building block for novel π-conjugated polymers with application potential in the n-channel semiconductors.

Self-assembled Quinacridone (QA) based polymers with strong hydrogen bonding for OFETs

For totally disordered organic polymer films, charge mobility is low, while the mobility significantly increases if the polymer exhibits self-assembling properties that can be exploited to generate ordered structures. Introducing a hydrogen-bonding functionality in the materials, resulting in hydrogen-bonded material superstructures, can be a suitable method to fulfil those critical requirements. To the best of our knowledge, the chromophores with hydrogen bonding ability are rarely investigated. Quinacridone (QA) with large π-conjugation system, planar structure as well as the amide and carbonyl groups, is attracted our attention. The hydrogen bonding association (NH…OC) can be formed between the amide groups and the carbonyl units from the QA core. In this work, the QA chromophore is, for the first time, introduced as the electron withdrawing unit in donor-acceptor type polymers for semiconductors. The hydrogen bonded polymers exhibit significantly large red shifted up to 192 nm, which indicates that the hydrogen bonding association in the QA system is powerful. In addition, the hydrogen bonding association led to the polymers not only from a disorder state and inferior crystallinity transferring into a more ordered structures with a block- or fiber-liked-shaped crystalline, but also a strong aggregation. This observation is beneficial for the hole transporting between the neighboring molecules. In addition, the HOMO energy levels have been improved after the hydrogen bonding association formation, which is advantage for the Ohmic contact formation. As a consequent, the hole transport mobility is significantly improved from 0.13 cm2 V−1 s−1–1.02 cm2 V−1 s−1. This work demonstrate that QA is a novel and promising electron-deficient building block with potential strong hydrogen bonding association for the high-performance semiconductor.

Functionalized Phenanthrene Imide-Based Polymers for n-Type Organic Thin-Film Transistors.

High-performing n-type polymers are crucial for the advance of organic electronics field, however strong electron-deficient building blocks with optimized physicochemical properties for constructing them are still limited. The imide-functionalized polycyclic aromatic hydrocarbons (PAHs) with extended π-conjugated framework, high electron deficiency and good solubility serve as promising candidates for developing high-performance n-type polymers. Among the PAHs, phenanthrene (PhA) features a well-delocalized aromatic π-system with multiple modifiable active sites . However, the PhA-based imides are seldom studied, mainly attributed to the synthetic challenge. Herein, we report two functionalized PhAs, CPOI and CPCNI, by simultaneously incorporating imide with carbonyl or dicyanomethylene onto PhA. Notably, the dicyanomethylene-modified CPCNI exhibits a well stabilized LUMO energy level (-3.84 eV), attributed to the synergetic inductive effect from imide and cyano groups. Subsequently, based on CPOI and CPCNI, two polymers PCPOI-Tz and PCPCNI-Tz were developed. Applied to organic thin-film transistors, owing to the strong electron-deficiency of CPCNI, polymer PCPCNI-Tz shows an improved electron mobility and largely decreased threshold voltage compared with PCPOI-Tz. This work affords two structurally novel electron-deficient building blocks and highlights the effectiveness of dual functionalization of PhAs with strong electron-withdrawing groups for devising n-type polymers.

Cyano-Functionalized Pyrazine: A Structurally Simple and Easily Accessible Electron-Deficient Building Block for n-Type Organic Thermoelectric Polymers.

Developing low-cost and high-performance n-type polymer semiconductors is essential to accelerate the application of organic thermoelectrics (OTEs). To achieve this objective, it is critical to design strong electron-deficient building blocks with simple structure and easy synthesis, which are essential for the development of n-type polymer semiconductors. Herein, we synthesized two cyano-functionalized highly electron-deficient building blocks, namely 3,6-dibromopyrazine-2-carbonitrile (CNPz) and 3,6-Dibromopyrazine-2,5-dicarbonitrile (DCNPz), which feature simple structures and facile synthesis. CNPz and DCNPz can be obtained via only one-step reaction and three-step reactions from cheap raw materials, respectively. Based on CNPz and DCNPz, two acceptor-acceptor (A-A) polymers, P(DPP-CNPz) and P(DPP-DCNPz) are successfully developed, featuring deep-positioned lowest unoccupied molecular orbital (LUMO) energy levels, which are beneficial to n-type organic thin-film transistors (OTFTs) and OTEs performance. An optimal unipolar electron mobility of 0.85 and 1.85 cm2 V-1 s-1 is obtained for P(DPP-CNPz) and P(DPP-DCNPz), respectively. When doped with N-DMBI, P(DPP-CNPz) and P(DPP-DCNPz) show high n-type electrical conductivities/power factors of 25.3 S cm-1 /41.4 μW m-1 K-2 , and 33.9 S cm-1 /30.4 μW m-1 K-2 , respectively. Hence, the cyano-functionalized pyrazine CNPz and DCNPz represent a new class of structurally simple, low-cost and readily accessible electron-deficient building block for constructing n-type polymer semiconductors.

N-type conjugated polymer semiconductor materials based on Aza-BODIPY dye with Naphthodipyrrolopyrrole (NDP-AB)

So far, the charge carrier mobility as well as the stability of n-type semiconductors fall behind when compared to the p-type ones. Therefore, exploring high-performance n-type semiconductor materials plays a crucial role in the further development of organic field-effect transistors (OFETs) for industrial applications. Naphthodipyrrolopyrrole-based dimeric aza-boron dipyrromethene dyes (NDP-AB) present strong electron-deficient units, which are rarely investigated. In this work, the NDP-AB chromophore is, for the first time, introduced as the acceptor in donor-acceptor type polymers. The results show that the NDP-AB based polymers exhibit extra-low LUMO energy levels, which endow the semiconductor layer with the ability to form Ohmic contacts with electrodes. This is advantageous for electron injection. In addition, the polymers present not only a strong aggregation as well as short π-π stacking d-spacing, but also a good planar polymer backbone and strong ICT effect. That phenomenon is advantage for the electron carrier transport across the adjacent molecules and the individual molecule. As a consequence, the NDP-AB-based polymers exhibit n-type behavior with electron transport mobility up to 0.89 cm2 V−1 s−1. This work demonstrate that NDP-AB is a promising electron-deficient building block for high-performance n-type semiconductors.

An asymmetric non-fused electron-deficient building block for low-cost polymer acceptor in all-polymer solar cells

An asymmetric non-fused electron-deficient building block for low-cost polymer acceptor in all-polymer solar cells

Semiconducting Polymers Based on Simple Electron-Deficient Cyanated trans-1, 3-Butadienes for Organic Field-Effect Transistors.

Developing high-performance but low-cost n-type polymers remains a significant challenge in the commercialization of organic field-effect transistors (OFETs). To achieve this objective, it is essential to design the key electron-deficient units with simple molecular structure and facile preparation process, which can directly facilitate the production of low-cost n-type polymers. Herein, by sequentially introducing fluorine and cyano functionalities onto trans-1,3-butadiene π-skeleton, we developed a series of structurally simple but highly electron-deficient building blocks, namely 1,4-dicyano-butadienes (CNDE), 3-fluoro-1,4-dicyano-butadienes (CNFDE), and 2,3-difluoro-1,4-dicyano-butadienes (CNDFDE), featuring highly coplanar backbone and deep-positioned lowest unoccupied molecular orbital (LUMO) energy levels (-3.03-4.33 eV), which render them highly attractive building blocks for developing n-type semiconducting polymers. Notably, all these electron-deficient units can be easily accessed via a two-step high-yield synthetic protocol from low-cost raw materials, thus rendering them highly promising candidates for commercial applications. Upon polymerized with diketopyrrolopyrrole (DPP) units, three copolymers are developed and demonstrated unipolar n-type transport characteristics in OFETs with the highest electron mobility > 1 cm2 V-1 s-1. Hence, CNDE, CNFDE, and CNDFDE represent a class of novel, simple, and efficient electron-deficient units for constructing low-cost n-type polymers, providing valuable insights for the OFET applications.

Synthesis and Optoelectronic Applications of dπ-pπ Conjugated Polymers with a Di-metallaaromatic Acceptor.

The development of conjugated polymers especially n-type polymer semiconductors is powered by the design and synthesis of electron-deficient building blocks. Herein, a strong acceptor building block with di-metallaaromatic structure was designed and synthesized by connecting two electron-deficient metallaaromatic units through a π-conjugated bridge. Then, a double-monomer polymerization methodology was developed for inserting it into conjugated polymer scaffolds to yield metallopolymers. The isolated well-defined model oligomers indicated polymer structures. Kinetic studies based on NMR and UV/Vis spectroscopies shed light on the polymerization process. Interestingly, the resulted metallopolymers with dπ-pπ conjugations are very promising electron transport layer materials which can boost photovoltaic performance of an organic solar cell, with power conversion efficiency up to 18.28% based on the PM6:EH-HD-4F non-fullerene system. This work not only provides a facile route to construct metallaaromatic conjugated polymers with various functional groups, but also discovers their potential applications for the first time.

A Competitive n‐Type OECT Material via Copolymerization of Electron Deficient Building Blocks

AbstractThe classical acceptor motifs diketopyrrolopyrrole (DPP) and thienopyrrolodione (TPD) are copolymerized to yield the acceptor–acceptor polymer “Poly(DPP‐TPD).” The fundamental design idea is to maximize the electron affinity (EA), thus increasing the ambient stability of the reduced state against oxygen and water while ensuring high ion compatibility through the incorporation of hydrophilic oligoethylene glycol N‐substituents. Additionally, a highly planarized polymer structure is anticipated, due to the extended noncovalent interactions (conformational locking) between the carbonyl oxygen and the thiophene protons. Cyclic voltammetry, spectroelectrochemistry, ultraviolet photoelectron spectroscopy, ultraviolet‐visible absorption spectroscopy, and organic field effect transistor (OFET) characterization demonstrate the suitability for n‐type organic electrochemical transistor (OECT) devices. High EA, ionization potential, and good electron mobility (µe(OFET)) are shown, in addition to the electrochemical reduction of polymer films in aqueous electrolyte. In n‐type OECTs, poly(DPP‐TPD) demonstrates a moderate threshold voltage of Vth = 0.58 V and an outstanding µC* value of 7.62 F cm−1 V−1 s−1. Cycling studies consisting of pulsed on‐ and off‐switching of the device at gate voltages between Vg = 0.6–0.8 V in the saturation regime reveal high stability for more than 2700 cycles with rapid switching kinetics.

A Cyano-Substituted Organoboron Electron-deficient Building Block for D-A Type Conjugated Polymers

A Cyano-Substituted Organoboron Electron-deficient Building Block for D-A Type Conjugated Polymers

Dithiene-fused quinoxalineimide-based all-acceptor polymers for n-type organic semiconductors

Integration of bithiophene imide (BTI) and quinoxaline (Qx) units into a new electron-deficient building block, dithiene-fused quinoxalineimide (DTQI), is an effective strategy for constructing n-type polymer semiconductors.

A croconic acid-derived narrow band gap conjugated microporous polymer.

Croconic acid, a novel highly electron-deficient building block, was introduced into a conjugated microporous polymer (CTPA). The CMP possesses strong donor-acceptor interactions, which resulted in near-IR absorption (red edge ∼1350 nm), a narrow bandgap (<1 eV) and high electrical conductivity upon doping (0.1 S m-1). Compared to the squaric acid congener (STPA), CTPA showed superior optical, electronic and electrical properties.

Cyano-functionalized organic and polymeric semiconductors for high-performance n-type organic electronic devices

Cyano functionalization as an effective strategy to construct high-performance n-type semiconductors is widely investigated in organic electronics.

A polymer donor based on difluoro-quinoxaline with a naphthalimide substituent unit exhibits a low-lying HOMO level for efficient non-fullerene polymer solar cells.

The design and synthesis of polymer donors with a low-lying highest occupied molecular orbital (HOMO) level are crucial for increasing open-circuit voltages (VOC) and achieving high-performance non-fullerene polymer solar cells. Here, we developed two copolymers using non-fluorinated or fluorinated thienyl-conjugated benzodithiophenes as electron donor units, and difluoro-quinoxaline with a naphthalimide substituent (DNB) as the electron acceptor unit. These copolymers, namely PDNB and PDNB-2F, exhibited deep HOMO levels owing to the strong electron-withdrawing ability of the naphthalimide substituent. Density-functional theory calculations demonstrated that the skeletons of the two copolymers featured good coplanarity. Owing to the fluorination, PDNB-2F displayed an increased absorption coefficient and deeper HOMO level than PDNB. Moreover, the blended film based on PDNB-2F:Y6 demonstrated enhanced carrier mobility, decreased bimolecular recombination as well as favorable phase-separation regions. Consequently, the PDNB-2F:Y6-based device yielded a superior power conversion efficiency (PCE) of 12.18%, whereas the device based on PDNB:Y6 showed a comparatively lower PCE of 8.83%. These results indicate that difluoro-quinoxaline with a naphthalimide substituent is a prospective electron-deficient building block to develop donor polymers with low-lying HOMO levels to achieve efficient non-fullerene polymer solar cells.

N-Type Polymer Semiconductors Based on Dithienylpyrazinediimide.

The development of n-type organic semiconductors critically relies on the design and synthesis of highly electron-deficient building blocks with good solubility and small steric hindrance. We report here a strongly electron-deficient dithienylpyrazinediimide (TPDI) and its n-type semiconducting polymers. The pyrazine substitution leads to the resulting polymers with much lower-lying lowest unoccupied molecular orbital (LUMO) levels and improved backbone planarity compared to the reported dithienylbenzodiimide (TBDI)- and fluorinated dithienylbenzodiimide (TFBDI)-based polymer analogues, thus yielding n-type transport character with an electron mobility up to 0.44 cm2 V-1 s-1 in organic thin-film transistors. These results demonstrate that dithienylpyrazinediimide is a highly promising electron-deficient building block for constructing high-performance n-type polymers and the incorporation of pyrazine into imide-functionalized (hetero)arenes is an effective strategy to develop n-type polymers with deep-lying frontier molecular orbital (FMO) levels for organic optoelectronic devices.

Bisaryl and Bisalkynyl Diruthenium (III,III) Compounds Based on an Electron-Deficient Building Block.

Reported herein is a new series of diruthenium(III,III) bisalkynyl and bisaryl diruthenium(III,III) compounds supported with 2-amino-3-(trifluoromethyl)pyridinate (amtfmp). Using Ru2(amtfmp)4Cl2 from a modified preparation, cis 2:2 Ru2(amtfmp)4(C≡CPh)2 (1), cis 2:2 Ru2(amtfmp)4(Ph)2 (2), and 3:1 Ru2(amtfmp)4(Ph)2 (3) were synthesized via a lithium-halogen exchange reaction using LiC2Ph and LiPh, respectively. Compounds 1-3 are all Ru2(III,III) species with a ground-state configuration of π4δ2(π*)4 (S = 0) and were characterized via mass spectrometry, electron absorption and 1H/19F NMR spectroscopies, and voltammetry. The molecular structures of 1-3 were established using single-crystal X-ray diffraction analysis, and preliminary density functional theory analysis was performed to elaborate the electronic structures of 1 and 2. Comparisons of the electrochemical properties of 1-3 against the Ru2(amtfmp)4Cl2 starting material reveal cathodic shifts of the Ru27+/6+ oxidation and the Ru26+/5+ and Ru25+/4+ reduction potentials. In comparison to related Ru2(III,III) bisalkynyl and bisaryl compounds, the electrode potentials for 1-3 are anodically shifted up to ca. 0.95 V, highlighting the strong electron-withdrawing nature of the amtfmp ligand.

A New Dibenzoquinoxalineimide-Based Wide-Bandgap Polymer Donor for Polymer Solar Cells.

The molecular design of a wide-bandgap polymer donor is critical to achieve high-performance organic photovoltaic devices. Herein, a new dibenzo-fused quinoxalineimide (BPQI) is successfully synthesized as an electron-deficient building block to construct donor–acceptor (D–A)-type polymers, namely P(BPQI-BDT) and P(BPQI-BDTT), using benzodithiophene and its derivative, which bears different side chains, as the copolymerization units. These two polymers are used as a donor, and the narrow bandgap (2,20-((2Z,20Z)-((12,13-bis(2-ethylhexyl)-3,9-diundecyl-12,13-dihydro-[1,2,5]thiadiazolo [3,4-e]thieno[2,″30′:4′,50]thieno[20,30:4,5]pyrrolo[3,2g]thieno[20,30:4,5]thieno[3,2-b]indole-2,10 diyl)bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene))dimalononitrile) Y6 is used as an acceptor to fabricate bulk heterojunction polymer solar cell devices. Y6, as a non-fullerene receptor (NFA), has excellent electrochemical and optical properties, as well as a high efficiency of over 18%. The device, based on P(BPQI-BDTT):Y6, showed power conversion efficiencies (PCEs) of 6.31% with a JSC of 17.09 mA cm−2, an open-circuit voltage (VOC) of 0.82 V, and an FF of 44.78%. This study demonstrates that dibenzo-fused quinoxalineimide is a promising building block for developing wide-bandgap polymer donors.

Solution Processable Benzotrithiophene (BTT)-Based Organic Semiconductors: Recent Advances and Review.

Conjugated polymers and small molecules (SMs) with fused electron-rich and electron-deficient building blocks are promising materials for low-cost organic electronic devices. Benzotrithiophene (BTT) is one such electron-rich hybrid building block composed of three fused thiophene moieties with an extended π-system that has been widely used to synthesize a variety of electronic materials. Additionally, BTT has a planar and sulfur-rich core with a number of distinct advantages, including structural diversity, tunable electro-optical properties and exceptional hole-transport behavior. So far, four BTT-based isomers have been synthesized on a gram scale from seven isomeric structures, three of which are symmetric (BTT1-3) and one of which is asymmetric (BTT5), for use in a variety of optoelectronic applications. However, no report summarizing the progress of BTT-based semiconductors for electronic applications is available. The current review presents an overview of the recent developments in BTT-based monomers, polymers and SMs, as well as their applications in energy harvesting. Additionally, recent advances on charge transport devices, most notably organic solar cells (OSCs), organic thin field-effect transistors (OTFTs), and perovskite solar cells (Pero-SCs) are also surveyed and summarized. It is anticipatedthat this comprehensive review will stimulate further research and development of future BTT-based electronic materials, particularly for low-cost and high-performance organic electronic devices.

Correction to “High-Performance Unipolar n-Type Conjugated Polymers Enabled by Highly Electron-Deficient Building Blocks Containing F and CN Groups”

Correction to “High-Performance Unipolar n-Type Conjugated Polymers Enabled by Highly Electron-Deficient Building Blocks Containing F and CN Groups”