High-speed and large-scale intrinsically stretchable integrated circuits.

Intrinsically stretchable electronics with skin-like mechanical properties have been identified as a promising platform for emerging applications ranging from continuous physiological monitoring to real-time analysis of health conditions, to closed-loop delivery of autonomous medical treatment1-7. However, current technologies could only reach electrical performance at amorphous-silicon level (that is, charge-carrier mobility of about 1 cm2 V-1 s-1), low integration scale (for example, 54 transistors per circuit) and limited functionalities8-11. Here we report high-density, intrinsically stretchable transistors and integrated circuits with high driving ability, high operation speed and large-scale integration. They were enabled by a combination of innovations in materials, fabrication process design, device engineering and circuit design. Our intrinsically stretchable transistors exhibit an average field-effect mobility of more than 20 cm2 V-1 s-1 under 100% strain, a device density of 100,000 transistors per cm2, including interconnects and a high drive current of around 2 µA µm-1 at a supply voltage of 5 V. Notably, these achieved parameters are on par with state-of-the-art flexible transistors based on metal-oxide, carbon nanotube and polycrystalline silicon materials on plastic substrates12-14. Furthermore, we realize a large-scale integrated circuit with more than 1,000 transistors and a stage-switching frequency greater than 1 MHz, for the first time, to our knowledge, in intrinsically stretchable electronics. Moreover, we demonstrate a high-throughput braille recognition system that surpasses human skin sensing ability, enabled by an active-matrix tactile sensor array with a record-high density of 2,500 units per cm2, and a light-emitting diode display with a high refreshing speed of 60 Hz and excellent mechanical robustness. The above advancements in device performance have substantially enhanced the abilities of skin-like electronics.

Electron-Deficient Polycyclic π-System Fused with Multiple B←N Coordinate Bonds.

An extensive polycyclic π-system with 23 fused rings is synthesized via a highly efficient borylation reaction, in which four B-N covalent bonds and four B←N coordinate bonds are formed in one pot. B←N coordinate bonds not only lock the backbone into a near-coplanar conformation but also decrease the LUMO energy level to around -3.82 eV, demonstrating the dual utility of this strategy for the synthesis of extensive rigid polycyclic molecules and the development of n-type conjugated materials for organic electronics and organic photovoltaics.

TEMPO Containing Radical Polymonothiocarbonate Polymers with Regio- and Stereo-Regularities: Synthesis, Characterization, and Electrical Conductivity Studies.

We report the synthesis of a (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl) (TEMPO) appended polymonothiocarbonates through the ring-opening copolymerization of (4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (GTEMPO) in the presence of carbonyl sulfide under ambient conditions. We have prepared the atactic and isotactic versions of this polymer, using enantiopure R or S forms of the GTEMPO monomer in the latter instances. Cyclic voltammetry studies revealed both oxidation and reduction events that were characteristic of TEMPO radicals. Electrical conductivity of these polymers was measured as solid-state films after annealing the samples above their glass transition temperatures. At room temperature the isotactic polymer shows much greater conductivity (ca. 10-4  S cm-1 ) than the atactic (ca. 10-7  S cm-1 ), attributed to the well-defined stereochemistry and regulated charge transport pathway of isotactic polymer chains in contrast to the irregular structure of the atactic counterpart.

Pauli Paramagnetism of Stable Analogues of Pernigraniline Salt Featuring Ladder-Type Constitution.

Polyaniline derivatives represent one of the most widely used classes of conductive polymers. The fundamentally important electronic properties of pernigraniline salts, the fully oxidized and acid-doped derivatives of polyanilines, however, are still not well-understood due to their poor stability and configurational uncertainty. To address these issues and to synthetically access stable analogues of pernigraniline salts, ladder-type constitution was imparted into a series of model oligomer analogues with rigid backbones constituted by up to 27 fused rings. The syntheses were achieved through iterative cross-coupling reactions followed by cyclization and oxidation. In contrast to their unstable non-ladder-type counterparts, these ladder-type pernigraniline-like molecules all adopt a well-defined all-trans configuration and demonstrate an excellent chemical stability after protonation, rendering it possible to reveal the intrinsic electronic and magnetic properties of molecules resembling pernigraniline. Protonated salts of these oligomers feature a significant diradicaloid open-shell resonance contribution. A dominant temperature-independent Pauli paramagnetism was observed in the solid state, an indication of the delocalization nature of the polarons in ladder-type analogues of pernigraniline salt.

Redox Communication between Two Diarylamido/Bis(phosphine) (PNP)M Moieties Bridged by Ynediyl Linkers (M = Ni, Pd, Pt).

A series of binuclear homo- and heterobimetallic complexes of the general type (PNP)M-[linker]-M(PNP) have been prepared (M = Ni, Pd, Pt; PNP = a diarylamido/bis(phosphine) pincer ligand; -[linker]- = -C≡C-, -C≡CC≡C-, -C≡CC6H4C≡C-). Each (PNP)M site can be oxidized by one electron, and this work reports the investigation of the mixed-valence behavior in terms of the communication between the two redox sites and the degree of the delocalization in the monooxidized cation. The compounds were evaluated using cyclic voltammetry, UV-vis-NIR and EPR spectroscopy, X-ray crystallography, and DFT calculations. The complex with the longest examined linker, (PNP)Ni-C≡CC6H4C≡C-Ni(PNP) (9Ni), exhibited no discernible communication between the redox sites. The homobimetallic complexes (PNP)M-C≡CC≡C-M(PNP) (6M) displayed a lower degree of communication in comparison to the -C≡C- linker analogues (PNP)M-C≡C-M(PNP) (3M). Within each of these two subsets, the relative degree of communication and delocalization was determined to be Pd < Ni ≤ Pt. On the Robin-Day scale, compounds 6M can be assigned class I for M = Pd and class II for M = Ni, Pt. Complex 3Pd also falls into class II, while 3Ni and 3Pt may be viewed as borderline class II/III cases. It is likely that the communication in the Ni systems has the advantage of the smaller size of Ni, resulting in a greater physical proximity of the redox sites, while the 5d metal Pt possesses the greatest ability for orbital interaction with the -C≡C- linker.

Deconvolution of fast exchange equilibrium states in NMR spectroscopy using virtual reference standards and probability theory.

A methodology for deconvolution of fast exchange equilibrium states in NMR spectroscopy (DFEQNMR) was developed based on DFT-GIAO NMR chemical shift prediction and a probability theory algorithm. Proof-of-concept studies were performed to estimate the protonation state of N-containing organic molecules involving fast proton exchange equilibrium and evaluate the solution tautomerism of a purine derivative. DFT-GIAO calculations were optimized to achieve good accuracy in 13C, 1H and 15N chemical shift prediction for protonated species. The probability theory algorithm enabled the determination of solution species ratios and yielded 95% confidence regions by comparing experimental and simulated chemical shift data sets. The calculation showed good accuracy for model partial salts with various functionalities and application in structure elucidation of complex natural product partial salts was also demonstrated. This method showed promising potential in acquisition of important insight into fast exchange equilibrium systems with only one experimental NMR chemical shift data set.

Advancing the Development of Highly-Functionalizable Glucose-Based Polycarbonates by Tuning of the Glass Transition Temperature.

Fundamental studies that gain an understanding of the tunability of physical properties of natural product-based polymers are vital for optimizing their performance in extensive applications. Variation of glass transition temperature ( Tg) was studied as a function of the side chain structure and molar mass for linear poly(glucose carbonate)s. A remarkable range of Tg values, from 38 to 125 °C, was accomplished with six different alkyloxycarbonyl side chains. The impact of molar mass on Tg was investigated for two series of polymers and discrete oligomers synthesized and fractionated with precise control over the degrees of polymerization. The Tg was found to be greatly influenced by a synergistic effect of the flexibility and bulkiness of the repeating unit side chain, as well as the chain end relative free volume. This work represents an important advance in the development of glucose-based polycarbonates, as materials that possess high degrees of functionalizability to be capable of exhibiting diversified physicochemical and thermal properties by simple side chain modification.

Extraordinary Redox Activities in Ladder-Type Conjugated Molecules Enabled by B ← N Coordination-Promoted Delocalization and Hyperconjugation.

The introduction of B ← N coordinate bond-isoelectronic to C-C single bond-into π-systems represents a promising strategy to impart exotic redox and electrochromic properties into conjugated organic molecules and macromolecules. To achieve both reductive and oxidative activities using this strategy, a cruciform ladder-type molecular constitution was designed to accommodate oxidation-active, reduction-active, and B ← N coordination units into a compact structure. Two such compounds (BN-F and BN-Ph) were synthesized via highly efficient N-directed borylation. These molecules demonstrated well-separated, two reductive and two oxidative electron-transfer processes, corresponding to five distinct yet stable oxidation states, including a rarely observed boron-containing radical cation. Spectroelectrochemical measurements revealed unique optical characteristics for each of these reduced/oxidized species, demonstrating multicolor electrochromism with excellent recyclability. Distinct color changes were observed between each redox state with clear isosbestic points on the absorption spectra. The underlying redox mechanism was elucidated by a combination of computational and experimental investigations. Single-crystal X-ray diffraction analysis on the neutral state, the oxidized radical cation, and the reduced dianion of BN-Ph revealed structural transformations into two distinct quinonoid constitutions during the oxidation and reduction processes, respectively. B ← N coordination played an important role in rendering the robust and reversible multistage redox properties, by extending the charge and spin delocalization, by modulating the π-electron density, and by a newly established hyperconjugation mechanism.

Chiral N-Phosphonyl Imines for an Aza-Morita-Baylis-Hillman Reaction via Group-Assisted Purification (GAP) Chemistry.

Seventeen examples of aza-Morita-Baylis-Hillman (aza-MBH) adducts have been synthesized by reacting chiral N-phosphonyl imines with acrylonitrile in good to excellent yields (up to 96%) and high diastereoselectivity (up to 99:1 dr). The synthesis of these adducts followed the method of group-assisted purification (GAP) chemistry, in which the pure aza-MBH products were readily obtained by washing the crude products with cosolvents of hexane and ethyl acetate.

Asymmetric aza-Morita-Baylis-Hillman reactions of chiral N-phosphonyl imines with acrylates via GAP chemistry/technology.

Chiral N-phosphonyl imines have been proven to be efficient electrophilic acceptors for asymmetric aza-Morita-Baylis-Hillman (aza-MBH) reactions with acrylates under convenient conditions. Thirty examples of ß-amino acrylates were generated in high yields (up to 99.4%) and diastereoselectivity (up to >99 : 1 dr) in an atom-economical fashion. The synthesis was proved to follow the GAP (group-assisted purification) chemistry, i.e., the pure products can be obtained simply by washing the crude products with hexane/ethyl acetate (v/v, 10/1) without the use of chromatography or recrystallization. DFT calculations were also conducted to support an asymmetric induction model accounting for high diastereoselectivity.

Synthesis and exceptional operational durability of polyaniline-inspired conductive ladder polymers.

Ladder-type structures can impart exceptional stability to polymeric electronic materials. This article introduces a new class of conductive polymers featuring a fully ladder-type backbone. A judicious molecular design strategy enables the synthesis of a low-defect ladder polymer, which can be efficiently oxidized and acid-doped to achieve its conductive state. The structural elucidation of this polymer and the characterization of its open-shell nature are facilitated with the assistance of studies on small molecular models. An autonomous robotic system is used to optimize the conductivity of the polymer thin film, achieving over 7 mS cm-1. Impressively, this polymer demonstrates unparalleled stability in strong acid and under harsh UV-irradiation, significantly surpassing commercial benchmarks like PEDOT:PSS and polyaniline. Moreover, it displays superior durability across numerous redox cycles as the active material in an electrochromic device and as the pseudocapacitive material in a supercapacitor device. This work provides structural design guidance for durable conductive polymers for long-term device operation.

Environmentally stable and stretchable polymer electronics enabled by surface-tethered nanostructured molecular-level protection.

Stretchable polymer semiconductors (PSCs) are essential for soft stretchable electronics. However, their environmental stability remains a longstanding concern. Here we report a surface-tethered stretchable molecular protecting layer to realize stretchable polymer electronics that are stable in direct contact with physiological fluids, containing water, ions and biofluids. This is achieved through the covalent functionalization of fluoroalkyl chains onto a stretchable PSC film surface to form densely packed nanostructures. The nanostructured fluorinated molecular protection layer (FMPL) improves the PSC operational stability over an extended period of 82 days and maintains its protection under mechanical deformation. We attribute the ability of FMPL to block water absorption and diffusion to its hydrophobicity and high fluorination surface density. The protection effect of the FMPL (~6 nm thickness) outperforms various micrometre-thick stretchable polymer encapsulants, leading to a stable PSC charge carrier mobility of ~1 cm2 V-1 s-1 in harsh environments such as in 85-90%-humidity air for 56 days or in water or artificial sweat for 42 days (as a benchmark, the unprotected PSC mobility degraded to 10-6 cm2 V-1 s-1 in the same period). The FMPL also improved the PSC stability against photo-oxidative degradation in air. Overall, we believe that our surface tethering of the nanostructured FMPL is a promising approach to achieve highly environmentally stable and stretchable polymer electronics.

Neuromorphic sensorimotor loop embodied by monolithically integrated, low-voltage, soft e-skin.

Artificial skin that simultaneously mimics sensory feedback and mechanical properties of natural skin holds substantial promise for next-generation robotic and medical devices. However, achieving such a biomimetic system that can seamlessly integrate with the human body remains a challenge. Through rational design and engineering of material properties, device structures, and system architectures, we realized a monolithic soft prosthetic electronic skin (e-skin). It is capable of multimodal perception, neuromorphic pulse-train signal generation, and closed-loop actuation. With a trilayer, high-permittivity elastomeric dielectric, we achieved a low subthreshold swing comparable to that of polycrystalline silicon transistors, a low operation voltage, low power consumption, and medium-scale circuit integration complexity for stretchable organic devices. Our e-skin mimics the biological sensorimotor loop, whereby a solid-state synaptic transistor elicits stronger actuation when a stimulus of increasing pressure is applied.

Thiazole fused S,N-heteroacene step-ladder polymeric semiconductors for organic transistors.

Ladder-type thiazole-fused S,N-heteroacenes with an extended π-conjugation consisting of six (SN6-Tz) and nine (SN9-Tz) fused aromatic rings have been synthesized and fully characterized. To date, the synthesis of well-defined fused building blocks and polymers of π-conjugated organic compounds based on the thiazole moiety is a considerable synthetic challenge, due to the difficulty in their synthesis. Acceptor-donor building blocks M1 and M2 were successfully polymerized into ladder homopolymers P1-P2 and further copolymerized with a diketopyrrolopyrrole unit to afford step-ladder copolymer P3. The optical, electronic, and thermal properties, in addition to their charge transport behavior in organic thin-film transistors (OTFTs), were investigated. The results showed an interesting effect on the molecular arrangement of the thiazole-based ladder-type heteroacene in the crystal structure revealing skewed π-π-stacking, and expected to possess better p-type semiconducting performance. The polymers all possess good molecular weights and excellent thermal properties. All the polymer-based OTFT devices exhibit annealing temperature dependent performance, and among the polymers P3 exhibits the highest mobility of 0.05 cm2 V-1 s-1.

Robust Jumping Actuator with a Shrimp-Shell Architecture.

It is highly desirable to develop compact- and robust-film jumping robots that can withstand severe conditions. Besides, the demands for strong actuation force, large bending curvature in a short response time, and good environmental tolerance are significant challenges to the material design. To address these challenges, this paper reports the fabrication of a thin-film jumping actuator, which exhibits a shrimp-shell architecture, from a conjugated ladder polymer (cLP) that is connected by carbon nanotube (CNT) sheets. The hierarchical porous structure ensures the fast absorption and desorption of organic vapor, thereby achieving a high response rate. The actuator does not exhibit shape distortion at temperatures of up to 225 °C and in concentrated sulfuric acid, as well as when immersed in many organic solvents. This work avails a new design strategy for high-performance actuators that function under harsh and complicated conditions.

Solution-processable porous graphitic carbon from bottom-up synthesis and low-temperature graphitization.

It is urgently desired yet challenging to synthesize porous graphitic carbon (PGC) in a bottom-up manner while circumventing the need for high-temperature pyrolysis. Here we present an effective and scalable strategy to synthesize PGC through acid-mediated aldol triple condensation followed by low-temperature graphitization. The deliberate structural design enables its graphitization in situ in solution and at low pyrolysis temperature. The resulting material features ultramicroporosity characterized by a sharp pore size distribution. In addition, the pristine homogeneous composition of the reaction mixture allows for solution-processability of the material for further characterization and applications. Thin films of this PGC exhibit several orders of magnitude higher electrical conductivity compared to analogous control materials that are carbonized at the same temperatures. The integration of low-temperature graphitization and solution-processability not only allows for an energy-efficient method for the production and fabrication of PGC, but also paves the way for its wider employment in applications such as electrocatalysis, sensing, and energy storage.

Extraordinary electrochemical stability and extended polaron delocalization of ladder-type polyaniline-analogous polymers.

Electrochemical stability and delocalization of states critically impact the functions and practical applications of electronically active polymers. Incorporation of a ladder-type constitution into these polymers represents a promising strategy to enhance the aforementioned properties from a fundamental structural perspective. A series of ladder-type polyaniline-analogous polymers are designed as models to test this hypothesis and are synthesized through a facile and scalable route. Chemical and electrochemical interconversions between the fully oxidized pernigraniline state and the fully reduced leucoemeraldine state are both achieved in a highly reversible and robust manner. The protonated pernigraniline form of the ladder polymer exhibits unprecedented electrochemical stability under highly acidic and oxidative conditions, enabling the access of a near-infrared light-absorbing material with extended polaron delocalization in the solid-state. An electrochromic device composed of this ladder polymer shows distinct switching between UV- and near-infrared-absorbing states with a remarkable cyclability, meanwhile tolerating a wide operating window of 4 volts. Taken together, these results demonstrate the principle of employing a ladder-type backbone constitution to impart superior electrochemical properties into electronically active polymers.

Synthesis and Solution Processing of a Rigid Polymer Enabled by Active Manipulation of Intramolecular Hydrogen Bonds.

Global intramolecular hydrogen bonds were installed and manipulated in a rigid artificial synthetic polymer in order to actively control its conformation for synthesis and processing. The polymer solubility was switched on and off by chemically inhibiting and regenerating these preorganized intramolecular hydrogen bonds. Such active manipulation made it possible to synthesize this highly rigid polymer with elevated molecular weights. A well-solubilized, noncoplanar polymer precursor with thermally cleavable Boc groups was synthesized (Mn = 32.4 kg/mol). After processing this precursor into thin films, in situ thermal treatment regenerated the latent intramolecular hydrogen bonds and led to a rigid ladder-type conformation. Such manipulation of the intramolecular hydrogen bonds allowed for multilayer deposition of this polymer, laying the foundation for potential additive manufacturing using this strategy.