β‑Alkyl substituted Dithieno[2,3‑<i>d</i>;2′,3′<i>-d</i>′]benzo[1,2‑<i>b</i>;4,5‑<i>b</i>′]dithiophene Semiconducting Materials and Their Application to Solution-Processed Organic Transistors

A novel highly π-extended heteroacene with four symmetrically fused thiophene-ring units and solubilizing substituents at the terminal β-positions on the central ring, dithieno­[2,3-<i>d</i>;2′,3′<i>-d</i>′]­benzo­[1,2-<i>b</i>;4,5-<i>b</i>′]­dithiophene (DTBDT) was synthesized via intramolecular electrophilic coupling reaction. The α-positions availability in the DTBDT motif enables the preparation of solution-processable DTBDT-based polymers such as <b>PDTBDT</b>, <b>PDTBDT-BT</b>, <b>PDTBDT-DTBT</b>, and <b>PDTBDT-DTDPP</b>. Even with its highly extended acene-like π-framework, all polymers show fairly good environmental stability of their highest occupied molecular orbitals (HOMOs) from −5.21 to −5.59 eV. In the course of our study to assess a profile of semiconductor properties, field-effect transistor performance of the four DTBDT-containing copolymers via solution-process is characterized, and <b>PDTBDT-DTDPP</b> exhibits the best electrical performance with a hole mobility of 1.70 × 10^–2 cm² V^–1 s^–1. <b>PDTBDT-DTDPP</b> has a relatively smaller charge injection barrier for a hole from the gold electrodes and maintains good coplanarity of the polymer backbone, indicating the enhanced π–π stacking characteristic and charge carrier transport. The experimental results demonstrate that our molecular design strategy for air-stable, high-performance organic semiconductors is highly promising

Solution-Processable Ambipolar Diketopyrrolopyrrole–Selenophene Polymer with Unprecedentedly High Hole and Electron Mobilities

There is a fast-growing demand for polymer-based ambipolar thin-film transistors (TFTs), in which both <i>n</i>-type and <i>p</i>-type transistor operations are realized in a single layer, while maintaining simplicity in processing. Research progress toward this end is essentially fueled by molecular engineering of the conjugated backbones of the polymers and the development of process architectures for device fabrication, which has recently led to hole and electron mobilities of more than 1.0 cm² V^–1 s^–1. However, ambipolar polymers with even higher performance are still required. By taking into account both the conjugated backbone and side chains of the polymer component, we have developed a dithienyl-diketopyrrolopyrrole (TDPP) and selenophene containing polymer with hybrid siloxane-solubilizing groups (<b>PTDPPSe-Si</b>). A synergistic combination of rational polymer backbone design, side-chain dynamics, and solution processing affords an enormous boost in ambipolar TFT performance, resulting in unprecedentedly high hole and electron mobilities of 3.97 and 2.20 cm² V^–1 s^–1, respectively

Boosting the Ambipolar Performance of Solution-Processable Polymer Semiconductors via Hybrid Side-Chain Engineering

Ambipolar polymer semiconductors are highly suited for use in flexible, printable, and large-area electronics as they exhibit both <i>n</i>-type (electron-transporting) and <i>p</i>-type (hole-transporting) operations within a single layer. This allows for cost-effective fabrication of complementary circuits with high noise immunity and operational stability. Currently, the performance of ambipolar polymer semiconductors lags behind that of their unipolar counterparts. Here, we report on the side-chain engineering of conjugated, alternating electron donor–acceptor (D–A) polymers using diketopyrrolopyrrole-selenophene copolymers with hybrid siloxane-solubilizing groups (<b>PTDPPSe-Si</b>) to enhance ambipolar performance. The alkyl spacer length of the hybrid side chains was systematically tuned to boost ambipolar performance. The optimized three-dimensional (3-D) charge transport of <b>PTDPPSe-Si</b> with pentyl spacers yielded unprecedentedly high hole and electron mobilities of 8.84 and 4.34 cm² V^–1 s^–1, respectively. These results provide guidelines for the molecular design of semiconducting polymers with hybrid side chains

Requirements for Forming Efficient 3‑D Charge Transport Pathway in Diketopyrrolopyrrole-Based Copolymers: Film Morphology vs Molecular Packing

To achieve extremely high planarity and processability simultaneously, we have newly designed and synthesized copolymers composed of donor units of 2,2′-(2,5-dialkoxy-1,4-phenylene)­dithieno­[3,2-<i>b</i>]­thiophene (TT-P-TT) and acceptor units of diketopyrrolopyrrole (DPP). These copolymers consist of a highly planar backbone due to intramolecular interactions. We have systematically investigated the effects of intermolecular interactions by controlling the side chain bulkiness on the polymer thin-film morphologies, packing structures, and charge transport. The thin-film microstructures of the copolymers are found to be critically dependent upon subtle changes in the intermolecular interactions, and charge transport dynamics of the copolymer based field-effect transistors (FETs) has been investigated by in-depth structure–property relationship study. Although the size of the fibrillar structures increases as the bulkiness of the side chains in the copolymer increases, the copolymer with the smallest side chain shows remarkably high charge carrier mobility. Our findings reveal the requirement for forming efficient 3-D charge transport pathway and highlight the importance of the molecular packing and interdomain connectivity, rather than the crystalline domain size. The results obtained herein demonstrate the importance of tailoring the side chain bulkiness and provide new insights into the molecular design for high-performance polymer semiconductors

Ambipolar Semiconducting Polymers with <i>π-</i>Spacer Linked Bis-Benzothiadiazole Blocks as Strong Accepting Units

Recognizing the importance of molecular coplanarity and with the aim of developing new, ideal strong acceptor-building units in semiconducting polymers for high-performance organic electronics, herein we present a simplified single-step synthesis of novel vinylene- and acetylene-linked bis-benzothiadiazole (<b>VBBT</b> and <b>ABBT</b>) monomers with enlarged planarity relative to a conventionally used acceptor, benzothiadiazole (BT). Along these lines, four polymers (<b>PDPP-VBBT</b>, <b>PDPP-ABBT</b>, <b>PIID-VBBT</b>, and <b>PIID-ABBT</b>) incorporating either <b>VBBT</b> or <b>ABBT</b> moieties are synthesized by copolymerizing with centro-symmetric ketopyrrole cores, such as diketopyrrolopyrrole (DPP) and isoindigo (IID), and their electronic, physical, and transistor properties are studied. These polymers show relatively balanced ambipolar transport, and <b>PDPP-VBBT</b> yields hole and electron mobilities as high as 0.32 and 0.13 cm² V^–1 s^–1, respectively. Interestingly, the acetylenic linkages lead to enhanced electron transportation in ketopyrrole-based polymers, showing a decreased threshold voltage and inverting voltage in the transistor and inverter devices, respectively. The IID-based BBT polymers exhibit the inversion of the dominant polarity depending on the type of unsaturated carbon bridge. Owing to their strong electron-accepting ability and their highly π-extended and planar structures, <b>VBBT</b> and <b>ABBT</b> monomers should be extended to the rational design of high-performance polymers in the field of organic electronics

Flexible FET-Type VEGF Aptasensor Based on Nitrogen-Doped Graphene Converted from Conducting Polymer

Graphene-based field-effect transistors (FETs) have been developed rapidly and are currently considered as an alternative for postsilicon electronics. In this study, polypyrrole-converted nitrogen-doped few-layer graphene (PPy-NDFLG) was grown on Cu substrate by chemical vapor deposition combined with vapor deposition polymerization and then transferred onto a flexible substrate. Furthermore, antivascular endothelial growth factor (VEGF) RNA aptamer conjugated PPy-NDFLG was integrated into a liquid-ion gated FET geometry to fabricate a high-performance VEGF aptamer-based sensor. Field-induced high sensitivity was observed for the analyte-binding events, eventually leading to the recognition of the target molecules at an unprecedentedly low concentration (100 fM). Additionally, the aptasensor had excellent reusability, mechanical bendability, and durability in the flexible process. The developed methodology describes, for the first time, the fabrication of N-doped graphene using conducting polymers including heteroatoms in their structures as the carbonization precursor and demonstrates its use in a high-performance, flexible FET-type aptasensor to detect vascular endothelial growth factor as a cancer biomarker