Multi-Functional 2D Covalent Organic Frameworks with Diketopyrrolopyrrole as Electron Acceptor.

2D covalent organic framework (COF) materials with extended conjugated structure and periodic columnar π-arrays exhibit promising applications in organic optoelectronics. However, there is a scarcity of reports on optoelectronic COFs, mainly due to the lack of suitable π-skeletons. Here, two multi-functional optoelectronic 2D COFs DPP-TPP-COF and DPP-TBB-COF are constructed with diketopyrrolopyrrole as electron acceptor (A), and 1,3,6,8-tetraphenylpyrene and 1,3,5-triphenylbenzene as electron donor (D) through imine bonds. Both 2D COFs showed good crystallinities and AA stacking with a rhombic framework for DPP-TPP-COF and hexagonal one for DPP-TBB-COF, respectively. The electron D-A and ordered intermolecular packing structures endow the COFs with broad UV-vis absorptions and narrow bandgaps along with suitable HOMO/LUMO energy levels, resulting in multi-functional optoelectronic properties, including photothermal conversion, supercapacitor property, and ambipolar semiconducting behavior. Among them, DPP-TPP-COF exhibits a high photothermal conversion efficiency of 47% under 660 nm laser irradiation, while DPP-TBB-COF exhibits superior specific capacitance of 384 F g-1. Moreover, P-type doping and N-type doping are achieved by iodine and tetrakis(dimethylamino)ethylene on a single host COF, resulting in ambipolar semiconducting behavior. These results provide a paradigm for the application of multi-functional optoelectronic COF materials.

Pre-Endcapping of Hyperbranched Polymers toward Intrinsically Stretchable Semiconductors with Good Ductility and Carrier Mobility.

The advancement of semiconducting polymers stands as a pivotal milestone in the quest to realize wearable electronics. Nonetheless, endowing semiconductor polymers with stretchability without compromising their carrier mobility remains a formidable challenge. This study proposes a "pre-endcapping" strategy for synthesizing hyperbranched semiconducting polymers (HBSPs), aiming to achieve the balance between carrier mobility and stretchability for organic electronics. The findings unveil that the aggregates formed by the endcapped hyperbranched network structure not only ensure efficient charge transport but also demonstrate superior tensile resistance. In comparison to linear conjugated polymers, HBSPs exhibit substantially larger crack onset strains and notably diminished tensile moduli. It is evident that the HBSPs surpass their linear counterparts in terms of both their semiconducting and mechanical properties. Among HBSPs, HBSP-72h-2.5 stands out as the preeminent candidate within the field of inherently stretchable semiconducting polymers, maintaining 93% of its initial mobility even when subjected to 100% strain (1.41 ± 0.206 cm2 V-1 s-1). Furthermore, thin film devices of HBSP-72h-2.5 remain stable after undergoing repeated stretching and releasing cycles. Notably, the mobilities are independent of the stretching directions, showing isotropic charge transport behavior. The preliminary study makes this "pre-endcapping" strategy a potential candidate for the future design of organic materials for flexible electronic devices.

Hyperbranched Polymers for Organic Semiconductors.

Hyperbranched polymers (HBPs) have attracted increasing attention owing to their distinct highly branched topological structures, resulting in unique properties and wide applications in organic semiconductors (OSCs). In this Review, recent progress in functional HBPs is outlined in the field of OSCs, including organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), dye-sensitized solar cells (DSSCs), and organic field effect transistors (OFETs), among others. Prospects of HBPs-based materials in OSCs are examined. The results revealed that multi-dimensional topologies not only regulate the electron (hole) transport but also adjust the film morphology, thereby affecting the efficiency and long life of organic electronic devices. Many studies showed the usefulness of HBPs as hole transport materials but reports dealing with n-type and ambipolar materials are still lacking. In addition, the interchain covalent bond in hyperbranched polymers could mitigate the damage caused by stretching, conducive to building stable flexible stretchable devices with long-term durability and good safety under harsh environmental conditions. Overall, the flexible stretchable design may enrich the applications of HBPs in organic semiconductors and provide new ideas for guiding the future design of functional organic semiconductor materials.

Non-symmetric Half-Fused B←N Coordinated Diketopyrrolopyrrole Building Block for n-type Semiconducting Polymers.

The development of conjugated polymers with high semiconducting performance and high reliability is of great significance for flexible electronics. Herein, we developed a new type of electron-accepting building block; i.e., non-symmetric half-fused B←N coordinated diketopyrrolopyrrole (DPP) (HBNDPP), for amorphous conjugated polymers toward flexible electronics. The rigid B←N fusion part of HBNDPP endows the resulting polymers with decent electron transport, while its non-symmetric structure causes the polymer to exhibit multiple conformation isomers with flat torsional potential energies. Thus, it gets packed in an amorphous manner in solid state, ensuring good resistance to bending strain. Combined with hardness and softness, the flexible organic field-effect transistor devices exhibit n-type charge properties with decent mobility, good bending resistance, and good ambient stability. The preliminary study makes this building block a potential candidate for future design of conjugated materials for flexible electronic devices.

Self-Doping Naphthalene Diimide Conjugated Polymers for Flexible Unipolar n-Type OTFTs.

The development of high-performance organic thin-film transistor (OTFT) materials is vital for flexible electronics. Numerous OTFTs are so far reported but obtaining high-performance and reliable OTFTs simultaneously for flexible electronics is still challenging. Herein, it is reported that self-doping in conjugated polymer enables high unipolar n-type charge mobility in flexible OTFTs, as well as good operational/ambient stability and bending resistance. New naphthalene diimide (NDI)-conjugated polymers PNDI2T-NM17 and PNDI2T-NM50 with different contents of self-doping groups on their side chains are designed and synthesized. The effects of self-doping on the electronic properties of resulting flexible OTFTs are investigated. The results reveal that the flexible OTFTs based on self-doped PNDI2T-NM17 exhibit unipolar n-type charge-carrier properties and good operational/ambient stability thanks to the appropriate doping level and intermolecular interactions. The charge mobility and on/off ratio are fourfold and four orders of magnitude higher than those of undoped model polymer, respectively. Overall, the proposed self-doping strategy is useful for rationally designing OTFT materials with high semiconducting performance and reliability.

Hyperbranched Diketopyrrolopyrrole-based Polymers Constructed via Linear Side-Chains towards Organic Field-Effect Transistors.

Conjugated polymers with high charge mobilities have drawn increasing attention in organic field-effect transistors (OFETs) in recent years. However, OFETs of conjugated polymers with high mobility and good device stability remain a challenge. In this article, we report a hyperbranched polymer approach to improve the charge mobility and device stability. Three hyperbranched diketopyrrolopyrrole-based polymers were designed and synthesized via linear alkyl side-chain linkers. The results show that 2D topological hyperbranched polymers form stable thin film microstructures, and thus improve the device stability, since the conjugated moiety is interconnected by linear alkyl chain. Besides, the incorporation of linear alkyl chain instead of branching alkyl one reduce steric hindrance, and improve the microstructure ordering as well as the charge mobility. Bar-coated OFETs result demonstrates that the devices mobilities and operational stabilities (bias stability and bending resistance) are both improved. All these indicate that hyperbranched polymer is a potential candidate for future application.