Closing the loop between microstructure and charge transport in conjugated polymers by combining microscopy and simulation.

A grand challenge in materials science is to identify the impact of molecular composition and structure across a range of length scales on macroscopic properties. We demonstrate a unified experimental-theoretical framework that coordinates experimental measurements of mesoscale structure with molecular-level physical modeling to bridge multiple scales of physical behavior. Here we apply this framework to understand charge transport in a semiconducting polymer. Spatially-resolved nanodiffraction in a transmission electron microscope is combined with a self-consistent framework of the polymer chain statistics to yield a detailed picture of the polymer microstructure ranging from the molecular to device relevant scale. Using these data as inputs for charge transport calculations, the combined multiscale approach highlights the underrepresented role of defects in existing transport models. Short-range transport is shown to be more chaotic than is often pictured, with the drift velocity accounting for a small portion of overall charge motion. Local transport is sensitive to the alignment and geometry of polymer chains. At longer length scales, large domains and gradual grain boundaries funnel charges preferentially to certain regions, creating inhomogeneous charge distributions. While alignment generally improves mobility, these funneling effects negatively impact mobility. The microstructure is modified in silico to explore possible design rules, showing chain stiffness and alignment to be beneficial while local homogeneity has no positive effect. This combined approach creates a flexible and extensible pipeline for analyzing multiscale functional properties and a general strategy for extending the accesible length scales of experimental and theoretical probes by harnessing their combined strengths.

Porous Semiconducting Polymer Nanoparticles as Intracellular Biophotonic Mediators to Modulate the Reactive Oxygen Species Balance.

The integration of nanotechnology with photoredox medicine has led to the emergence of biocompatible semiconducting polymer nanoparticles (SPNs) for the optical modulation of intracellular reactive oxygen species (ROS). However, the need for efficient photoactive materials capable of finely controlling the intracellular redox status with high spatial resolution at a nontoxic light density is still largely unmet. Herein, highly photoelectrochemically efficient photoactive polymer beads are developed. The photoactive material/electrolyte interfacial area is maximized by designing porous semiconducting polymer nanoparticles (PSPNs). PSPNs are synthesized by selective hydrolysis of the polyester segments of nanoparticles made of poly(3-hexylthiophene)-graft-poly(lactic acid) (P3HT-g-PLA). The photocurrent of PSPNs is 4.5-fold higher than that of nonporous P3HT-g-PLA-SPNs, and PSPNs efficiently reduce oxygen in an aqueous environment. PSPNs are internalized within endothelial cells and optically trigger ROS generation with a >1.3-fold concentration increase with regard to nonporous P3HT-SPNs, at a light density as low as a few milliwatts per square centimeter, fully compatible with in vivo, chronic applications.

Achieving Ideal and Environmentally Stable n-Type Charge Transport in Polymer Field-Effect Transistors.

Realizing ideal charge transport in field-effect transistors (FETs) of conjugated polymers is crucial for evaluating device performance, such as carrier mobility and practical applications of conjugated polymers. However, the current FETs using conjugated polymers as the active layers generally show certain non-ideal transport characteristics and poor stability. Here, ideal charge transport of n-type polymer FETs is achieved on flexible polyimide substrates by using an organic-inorganic hybrid double-layer dielectric. Deposited conjugated polymer films show highly ordered structures and low disorder, which are supported by grazing-incidence wide-angle X-ray scattering, near-edge X-ray absorption fine structure, and molecular dynamics simulations. Furthermore, the organic-inorganic hybrid double-layer dielectric provides low interfacial defects, leading to excellent charge transport in FETs with high electron mobility (1.49 ± 0.46 cm2 V-1 s-1) and ideal reliability factors (102 ± 7%). Fabricated polymer FETs show a self-encapsulation effect, resulting in high stability of the FET charge transport. The polymer FETs still work with high mobility above 1 cm2 V-1 s-1 after storage in air for more than 300 days. Compared with state-of-the-art conjugated polymer FETs, this work simultaneously achieves ideal charge transport and environmental stability in n-type polymer FETs, facilitating rapid device optimization of high-performance polymer electronics.

Urea-Comprising Single Core Diketopyrrolopyrrole Derivatives: Exploring the Synthesis, Self-Assembly and Charge Transport Properties.

Supramolecular electronics exploits the distinctive features stemming from noncovalent interactions, guiding the self-assembly of molecules to craft materials endowed with customized electronic functionalities. Hydrogen-bonded materials, characterized by their capacity to establish dynamic and stable networks, introduce an extra dimension to the development of supramolecular electronic systems. This study presents a comparative analysis of two remarkably small semiconductors utilizing diketopyrrolopyrrole functionalized with urea units as hydrogen-bonding motifs, strategically positioned at opposing ends of the conjugated core. We show how the subtle distinction in functionalization not only influences morphology and self-assembly dynamics via hydrogen-bonding and π-π stacking formation, but also holds significant consequences for ultimate charge transport properties. Our observations into the interplay of noncovalent interactions provide valuable insights and strategic pathways for the design of novel materials with enhanced electronic characteristics.

Inherent D-A Architecture in Indoloquinoxalines with an Array of Substituents for Non-Volatile Memory Device Applications.

Donor-acceptor (D-A)-based architecture has been the key to increase storage capability efficiency through the enhanced charge transportation in the fabricated device. We have designed and synthesized a series of functionalized indoloquinoxalines (IQ) for non-volatile organic memory devices. The investigation on UV-visible spectra reveals the absorption maxima of the compounds around 420 nm, attributed to the intramolecular charge transfer between indole and quinoxaline moiety. The irreversible anodic peak in the 1.0 to 1.5 V range indicates the indole moiety's oxidation ability. Besides, the cathodic peak in the range of -0.5 to -1.0 V, contributed to the stability of the reduced quinoxaline unit. All the compounds exhibited uniformly covered thin film in SEM analysis, potentially facilitating the seamless charge carrier migration between adjacent molecules. The methoxyphenyl substituted compound exhibited the binary write-once read-many (WORM) memory behavior with the lowest threshold voltage of -0.81 V. The molecular simulations displayed the efficient intramolecular charge transfer, providing the fabricated device's distinctive conductive states. Except for the tert-butylphenyl compound, which showed volatile dynamic random-access memory (DRAM) behavior, all the other compounds exhibited non-volatile WORM memory behavior, suggesting IQs potential as an intrinsic D-A molecule in organic memory devices on further structural refinement.

Relating Structure to Properties in Non-Conjugated Pendant Electroactive Polymers.

Non-conjugated pendant electroactive polymers (NCPEPs) are an emerging class of polymers that offer the potential of combining the desirable optoelectronic properties of conjugated polymers with the superior synthetic methodologies and stability of traditional non-conjugated polymers. Despite an increasing number of studies focused on NCPEPs, particularly on understanding fundamental structure-property relationships, no attempts have been made to provide an overview on established relationships to date. This review showcases selected reports on NCPEP homopolymers and copolymers that demonstrate how optical, electronic, and physical properties of the polymers are affected by tuning of key structural variables such as the chemical structure of the polymer backbone, molecular weight, tacticity, spacer length, the nature of the pendant group, and in the case of copolymers the ratios between different comonomers and between individual polymer blocks. Correlation of structural features with improved π-stacking and enhanced charge carrier mobility serve as the primary figures of merit in evaluating impact on NCPEP properties. While this review is not intended to serve as a comprehensive summary of all reports on tuning of structural parameters in NCPEPs, it highlights relevant established structure-property relationships that can serve as a guideline for more targeted design of novel NCPEPs in the future.

Applications of Functional Polymeric Eutectogels.

Over the past two decades, deep eutectic solvents (DESs) have captured significant attention as an emergent class of solvents that have unique properties and applications in differing fields of chemistry. One area where DES systems find utility is the design of polymeric gels, often referred to as "eutectogels," which can be prepared either using a DES to replace a traditional solvent, or where monomers form part of the DES themselves. Due to the extensive network of intramolecular interactions (e.g., hydrogen bonding) and ionic species that exist in DES systems, polymeric eutectogels often possess appealing material properties-high adhesive strength, tuneable viscosity, rapid polymerization kinetics, good conductivity, as well as high strength and flexibility. In addition, non-covalent crosslinking approaches are possible due to the inherent interactions that exist in these materials. This review considers several key applications of polymeric eutectogels, including organic electronics, wearable sensor technologies, 3D printing resins, adhesives, and a range of various biomedical applications. The design, synthesis, and properties of these eutectogels are discussed, in addition to the advantages of this synthetic approach in comparison to traditional gel design. Perspectives on the future directions of this field are also highlighted.

An organic transistor matrix for multipoint intracellular action potential recording.

Electrode arrays are widely used for multipoint recording of electrophysiological activities, and organic electronics have been utilized to achieve both high performance and biocompatibility. However, extracellular electrode arrays record the field potential instead of the membrane potential itself, resulting in the loss of information and signal amplitude. Although much effort has been dedicated to developing intracellular access methods, their three-dimensional structures and advanced protocols prohibited implementation with organic electronics. Here, we show an organic electrochemical transistor (OECT) matrix for the intracellular action potential recording. The driving voltage of sensor matrix simultaneously causes electroporation so that intracellular action potentials are recorded with simple equipment. The amplitude of the recorded peaks was larger than that of an extracellular field potential recording, and it was further enhanced by tuning the driving voltage and geometry of OECTs. The capability of miniaturization and multiplexed recording was demonstrated through a 4 × 4 action potential mapping using a matrix of 5- × 5-µm2 OECTs. Those features are realized using a mild fabrication process and a simple circuit without limiting the potential applications of functional organic electronics.

Modulation of Properties in [1]Benzothieno[3,2-b][1]benzothiophene Derivatives through Sulfur Oxidation.

This study explores the impact of sulfur oxidation on the structural, optical, and electronic properties of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives, specifically focusing on 2,7-dibromo BTBT (2,7-diBr-BTBT) and its oxidized forms, 5,5-dioxide (2,7-diBr-BTBTDO) and 5,5,10,10-tetraoxide (2,7-diBr-BTBTTO). The bromination of BTBT followed by sequential oxidation with m-chloroperoxybenzoic acid yielded the target compounds in good yields. They were characterized using a wide array of analytical techniques including different spectroscopic methods, X-ray analysis, thermal analysis, and quantum chemical calculations. The results revealed that sulfur oxidation significantly alters the crystal packing, thermal stability, and optoelectronic properties of BTBT derivatives. Notably, the oxidized forms exhibited increased thermal stability and enhanced emission properties, with quantum yields exceeding 99%. These findings provide valuable insights for designing advanced organic semiconductors and fluorescent materials with tunable properties, based on the BTBT core.

Organic Transistors Based on Highly Crystalline Donor-Acceptor π-Conjugated Polymer of Pentathiophene and Diketopyrrolopyrrole.

Oligomers and polymers consisting of multiple thiophenes are widely used in organic electronics such as organic transistors and sensors because of their strong electron-donating ability. In this study, a solution to the problem of the poor solubility of polythiophene systems was developed. A novel π-conjugated polymer material, PDPP-5Th, was synthesized by adding the electron acceptor unit, DPP, to the polythiophene system with a long alkyl side chain, which facilitated the solution processing of the material for the preparation of devices. Meanwhile, the presence of the multicarbonyl groups within the DPP molecule facilitated donor-acceptor interactions in the internal chain, which further improved the hole-transport properties of the polythiophene-based material. The weak forces present within the molecules that promoted structural coplanarity were analyzed using theoretical simulations. Furthermore, the grazing incidence wide-angle X-ray scanning (GIWAXS) results indicated that PDPP-5Th features high crystallinity, which is favorable for efficient carrier migration within and between polymer chains. The material showed hole transport properties as high as 0.44 cm2 V-1 s-1 in conductivity testing. Our investigations demonstrate the great potential of this polymer material in the field of optoelectronics.

Incorporation of Diketopyrrolopyrrole into Polythiophene for the Preparation of Organic Polymer Transistors.

Polythiophene, as a class of potential electron donor units, is widely used in organic electronics such as transistors. In this work, a novel polymeric material, PDPPTT-FT, was prepared by incorporating the electron acceptor unit into the polythiophene system. The incorporation of the DPP molecule assists in improving the solubility of the material and provides a convenient method for the preparation of field effect transistors via subsequent solution processing. The introduction of fluorine atoms forms a good intramolecular conformational lock, and theoretical calculations show that the structure displays excellent co-planarity and regularity. Grazing incidence wide-angle X-ray (GIWAXS) results indicate that the PDPPTT-FT is highly crystalline, which facilitates carrier migration within and between polymer chains. The hole mobility of this π-conjugated material is as high as 0.30 cm2 V-1 s-1 in organic transistor measurements, demonstrating the great potential of this polymer material in the field of optoelectronics.

Optimizing Upconversion Quantum Yield via Structural Tuning of Dipyrrolonaphthyridinedione Annihilators.

Triplet-triplet annihilation upconversion (TTA-UC) is a photophysical process in which two low-energy photons are converted into one higher-energy photon. This type of upconversion requires two species: a sensitizer that absorbs low-energy light and transfers its energy to an annihilator, which emits higher-energy light after TTA. In spite of the multitude of applications of TTA-UC, few families of annihilators have been explored. In this work, we show dipyrrolonaphthyridinediones (DPNDs) can act as annihilators in TTA-UC. We found that structural changes to DPND dramatically increase its upconversion quantum yield (UCQY). Our optimized DPND annihilator demonstrates a high maximum internal UCQY of 9.4%, outperforming the UCQY of commonly used near-infrared-to-visible annihilator rubrene by almost double.

An n-Type Conjugated Polymer with Low Crystallinity for High-Performance Organic Thermoelectrics.

Conjugated polymers (CPs) with low crystallinity are promising candidates for application in organic thermoelectrics (OTEs), particularly in flexible devices, because the disordered structures of these CPs can effectively accommodate dopants and ensure robust resistance to bending. However, n-doped CPs usually exhibit poor thermoelectric performance, which hinders the development of high-performance thermoelectric generators. Herein, we report an n-type CP (ThDPP-CNBTz) comprising two acceptor units: a thiophene-flanked diketopyrrolopyrrole and a cyano-functionalized benzothiadiazole. ThDPP-CNBTz shows a low LUMO energy level of below -4.20 eV and features low crystallinity, enabling high doping efficiency. Moreover, the dual-acceptor design enhances polaron delocalization, resulting in good thermoelectric performance. After n-doping, ThDPP-CNBTz exhibits an average electrical conductivity (σ) of 50.6 S cm-1 and a maximum power factor (PF) of 126.8 µW m-1 K-2, which is among the highest values reported for solution-processed n-type CPs to date. Additionally, a solution-processed flexible OTE device based on doped ThDPP-CNBTz exhibits a maximum PF of 70 µW m-1 K-2; the flexible device also shows remarkable resistance to bending strain, with only a marginal change in σ after 600 bending cycles. The findings presented in this work will advance the development of n-type CPs for OTE devices, and flexible devices in particular.

π-Conjugated Nanohoops: A New Generation of Curved Materials for Organic Electronics.

Nanohoops, cyclic association of π-conjugated systems to form a hoop-shaped molecule, have been widely developed in the last 15 years. Beyond the synthetic challenge, the strong interest towards these molecules arises from their radially oriented π-orbitals, which provide singular properties to these fascinating structures. Thanks to their particular cylindrical arrangement, this new generation of curved molecules have been already used in many applications such as host-guest complexation, biosensing, bioimaging, solid-state emission and catalysis. However, their potential in organic electronics has only started to be explored. From the first incorporation as an emitter in a fluorescent organic light emitting diode (OLED), to the recent first incorporation as a host in phosphorescent OLEDs or as charge transporter in organic field-effect transistors and in organic photovoltaics, this field has shown important breakthroughs in recent years. These findings have revealed that curved materials can play a key role in the future and can even be more efficient than their linear counterparts. This can have important repercussions for the future of electronics. Time has now come to overview the different nanohoops used to date in electronic devices in order to stimulate the future molecular designs of functional materials based on these macrocycles.

Spirobifluorene Trimers: High Triplet Pure Hydrocarbon Hosts for Highly Efficient Blue Phosphorescent Organic Light-Emitting Diodes.

Pure aromatic hydrocarbon materials (PHCs) represent a new generation of host materials for phosphorescent OLEDs (PhOLEDs), free of heteroatoms. They reduce the molecular complexity, can be easily synthesized and are an important direction towards robust devices. As heteroatoms can be involved in bonds dissociations in operating OLEDs through exciton induced degradation processes, developing novel PHCs appear particularly relevant for the future of this technology. In the present work, we report a series of extended PHCs constructed by the assembly of three spirobifluorene fragments. The resulting positional isomers present a high triplet energy level, a wide HOMO/LUMO difference and improved thermal and morphological properties compared to previously reported PHCs. These characteristics are beneficial for the next generation of host materials for PhOLEDs and provide relevant design guidelines. When used as a host in blue-emitting PhOLEDs, which are still the weakest link of the field, a very high EQE of 24 % and low threshold voltage of 3.56 V were obtained with a low-efficiency roll-off. This high performance strengthens the position of PHC strategy as an efficient alternative for OLED technology and opens the way to a more simple electronic.

Regional Functionalization Molecular Design Strategy: A Key to Enhancing the Efficiency of Multi-Resonance OLEDs.

Herein, we propose a regional functionalization molecular design strategy that enables independent control of distinct pivotal parameters through different molecule segments. Three novel multiple resonances thermally activated delayed fluorescence (MR-TADF) emitters A-BN, DA-BN, and A-DBN, have been successfully synthesized by integrating highly rigid and three-dimensional adamantane-containing spirofluorene units into the MR framework. These molecules form two distinctive functional parts: part 1 comprises a boron-nitrogen (BN)-MR framework with adjacent benzene and fluorene units forming a central luminescent core characterized by an exceptionally rigid planar geometry, allowing for narrow FWHM values; part 2 includes peripheral mesitylene, benzene, and adamantyl groups, creating a unique three-dimensional "umbrella-like" conformation to mitigate intermolecular interactions and suppress exciton annihilation. The resulting A-BN, DA-BN, and A-DBN exhibit remarkably narrow FWHM values ranging from 18 to 14 nm and near-unity photoluminescence quantum yields. Particularly, OLEDs based on DA-BN and A-DBN demonstrate outstanding efficiencies of 35.0 % and 34.3 %, with FWHM values as low as 22 nm and 25 nm, respectively, effectively accomplishing the integration of high color purity and high device performance.

A Hammett's analysis of the substituent effect in functionalized diketopyrrolopyrrole (DPP) systems: Optoelectronic properties and intramolecular charge transfer effects.

Diketopyrrolopyrrole (DPP) systems have promising applications in different organic electronic devices. In this work, we investigated the effect of 20 different substituent groups on the optoelectronic properties of DPP-based derivatives as the donor ( D )-material in an organic photovoltaic (OPV) device. For this purpose, we employed Hammett's theory (HT), which quantifies the electron-donating or -withdrawing properties of a given substituent group. Machine learning (ML)-based σ m , σ p , σ m 0 , σ p 0 , σ p + , σ p - , σ I , and σ R Hammett's constants previously determined were used. Mono- (DPP-X1 ) and di-functionalized (DPP-X2 ) DPPs, where X is a substituent group, were investigated using density functional theory (DFT), time-dependent DFT (TDDFT), and ab initio methods. Several properties were computed using CAM-B3LYP and the second-order algebraic diagrammatic construction, ADC(2), an ab initio wave function method, including the adiabatic ionization potential ( I P A ), the electron affinity ( E A A ), the HOMO-LUMO gaps ( E g ), and the maximum absorption wavelengths ( λ max ), the first excited state transition 1 S0 → 1 S1 energies ( ∆ E ) (the optical gap), and exciton binding energies. From the optoelectronic properties and employing typical acceptor systems, the power conversion efficiency ( PCE ), open-circuit voltage ( V OC ), and fill factor ( FF ) were predicted for a DPP-based OPV device. These photovoltaic properties were also correlated with the machine learning (ML)-based Hammett's constants. Overall, good correlations between all properties and the different types of σ constants were obtained, except for the σ I constants, which are related to inductive effects. This scenario suggests that resonance is the main factor controlling electron donation and withdrawal effects. We found that substituent groups with large σ values can produce higher photovoltaic efficiencies. It was also found that electron-withdrawing groups (EWGs) reduced E g and ∆ E considerably compared to the unsubstituted DPP-H. Moreover, for every decrease (increase) in the values of a given optoelectronic property of DPP-X1 systems, a more significant decrease (increase) in the same values was observed for the DPP-X2 , thus showing that the addition of the second substituent results in a more extensive influence on all electronic properties. For the exciton binding energies, an unsupervised machine learning algorithm identified groups of substituents characterized by average values (centroids) of Hammett's constants that can drive the search for new DDP-derived materials. Our work presents a promising approach by applying HT on molecular engineering DPP-based molecules and other conjugated molecules for applications on organic optoelectronic devices.

A comprehensive analysis of charge transfer effects on donor-pyrene (bridge)-acceptor systems using different substituents.

The alternant polycyclic aromatic hydrocarbon pyrene has photophysical properties that can be tuned with different donor and acceptor substituents. Recently, a D (donor)-Pyrene (bridge)-A (acceptor) system, DPA, with the electron donor N,N-dimethylaniline (DMA), and the electron acceptor trifluoromethylphenyl (TFM), was investigated by means of time-resolved spectroscopic measurements (J. Phys. Chem. Lett. 2021, 12, 2226-2231). DPA shows great promise for potential applications in organic electronic devices. In this work, we used the ab initio second-order algebraic diagrammatic construction method ADC(2) to investigate the excited-state properties of a series of analogous DPA systems, including the originally synthesized DPAs. The additionally investigated substituents were amino, fluorine, and methoxy as donors and nitrile and nitro groups as acceptors. The focus of this work was on characterizing the lowest excited singlet states regarding charge transfer (CT) and local excitation (LE) characters. For the DMA-pyrene-TFM system, the ADC(2) calculations show two initial electronic states relevant for interpreting the photodynamics. The bright S1 state is locally excited within the pyrene moiety, and an S2 state is localized ~0.5 eV above S1 and characterized as a donor to pyrene CT state. HOMO and LUMO energies were employed to assess the efficiency of the DPA compounds for organic photovoltaics (OPVs). HOMO-LUMO and optical gaps were used to estimate power conversion and light-harvesting efficiencies for practical applications in organic solar cells. Considering the systems using smaller D/A substituents, compounds with the strong acceptor NO2 substituent group show enhanced CT and promising properties for use in OPVs. Some of the other compounds with small substituents are also found to be competitive in this regard.

Hexakis-TIPS-Alkynylated Nonacenes: Persistent and Processible.

Four substituted nonacenes were prepared and characterized by UV-vis and EPR spectroscopy and X-ray crystallography. The compounds are the most stable and soluble nonacenes to date - due to six strategically placed triisopropylsilyl(TIPS)-ethynyl groups. They are stable for several weeks in the solid state. In dilute solution their half-life is 5-9 h. Crystal structure analyses of two nonacenes prove their structures. A nonacene derivative was tested in a solution-processed transistor and exhibits ambipolar charge transport (µe =0.007 cm2 /Vs; µh =0.023 cm2 /Vs).

High-Performance Organic Field-effect Transistors from Functionalized Zinc Meso-Porphyrins.

A series of new zinc porphyrins were synthesized, and their charge transport property was tuned by introducing various groups. Triarylamine was introduced to the porphyrin moiety at the meso-position as an electron donor, enhancing the charge carrier mobility. All the synthesized zinc porphyrins are thermally stable with a decomposition temperature over 178 °C. High frontier molecular orbitals levels of these compounds make them stable donor materials. SEM analysis of zinc porphyrins fabricated by spin-coating resulted in diversely self-assembled films. Field-effect transistors were fabricated using bottom-gate/top-contact architecture (BGTC) by solution-processable technique. The higher charge carrier mobility of 5.17 cm2 /Vs with on/off of 106 was obtained for trifluoromethyl substituted compound due to better molecular packing. In addition, GIXRD analysis revealed zinc porphyrins films crystalline nature, which supports its better charge carrier mobility. The present investigation has validated that zinc porphyrin building blocks are an attractive candidate for p-channel OFET devices.