Soluble Acenes Research Articles

Crystal Engineering Under Residual Solvent Evaporation: A Journey Into Crystallization Chronicles of Soluble Acenes.

In the pursuit of achieving high-performance and high-throughput organic transistors, this study highlights two critical aspects: designing new soluble acenes and optimizing their solution processing. A fundamental understanding of the crystallization mechanism inherent to these customized soluble acenes, as they undergo a transformation during the evaporation of residual solvent, is deemed essential. Here, the pathway to crafting ideal solution processing conditions is elucidated, meticulously tailored to the molecular structure of soluble acenes when blended with polymers. Employing a comprehensive array of analytical and computational methodologies, this investigation delves directly into the intricate interplay between processing parameters and crystallization mechanisms, firmly rooted in the domains of thermodynamics and kinetics. Notably, a delicate equilibrium where the optimal weight of residual solvent harmoniously aligns is uncovered with the specific attributes of soluble acene molecules, exerting influence over vertical phase separation with the blended polymer and the crystallization process of soluble acenes at the surface. Consequently, transistors showcasing remarkable field-effect mobility exceeding 8 cm2V-1s-1 are successfully developed. These findings provide invaluable guidance for navigating the path toward determining optimal solution processing conditions across a diverse array of soluble acene/polymer blend systems, all achieved through the strategic application of crystal and residual solvent engineering.

How to Stabilize Large Soluble (Hetero-)Acenes.

The higher acenes and azaacenes (>(aza)heptacenes) are fascinating, yet elusive materials. Their reactivity and sensitivity increases concomitantly with their size. In recent years, confinement techniques, that is isolation of acenes in matrices and on surfaces, has surpassed solution-based chemistry with respect to accessing the larger (hetero)acenes at the price of the accessibility of no more than a couple thousands of molecules. Isolating acenes in bulk quantities and in processable form is vital for applications in organic electronics as well as from a viewpoint from basic research. In this Perspective, we will discuss after a short historical outline their degradation pathways, and then will selectively highlight recent efforts in stabilizing soluble (aza)acenes.

Pentacene to Octacene: The Limit of Fourfold TIPS-Ethynylation

Soluble acenes beyond hexacene are rare. Their sensitivity complicates isolation, purification and application in devices. To increase the stability of acenes, functionalization with trialkylsilylethynyl substituents prevents [4 + 4] dimerization and oxidation. At the same time, such acenes are soluble and processible. Here we present the modular synthesis of fourfold tri-iso-propylsilylethynyl-ethynylated pentacenes to octacenes and investigate their optical and redox properties, frontier orbital positions (CV, density functional theory calculations) as well as their stability in solution (UV/vis, NMR spectroscopy). We also investigated their magnetic properties as a function of acene length. Pentacene, hexacene and heptacene are sufficiently stable to serve as semiconductors in thin-film transistors – the octacene rapidly decays to its butterfly dimer evidence by time-dependent NMR spectroscopy and crystal structure analysis.

Marangoni Flow Driven via Hole Structure of Soluble Acene–Polymer Blends for Selective Nitrogen Dioxide Sensing

AbstractThe correlations between semiconductor type and gas sensing properties in soluble acene/polymer blends have not yet been examined. Here, the phase separation mechanism in pseudo‐liquid phase blend film is investigated and an unusual solid‐state morphology that is effective for amperometric gas sensing performance is demonstrated. In 6,13‐bis(triisopropylsilylethynyl) pentacene (TIPS–pentacene)/poly(fluorine‐co‐triarylamine) (PTAA) blend, two phases are uniformly mixed, without being completely phase‐separated due to the similar solubility and surface tension. On the other hand, in 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl) anthradithiophene (diF–TES ADT)/PTAA blend, the diF−TES ADT molecules are segregated both at the air–film, and film–substrate interfaces, and subsequently crystallized with a high degree of crystal perfection. In the meanwhile, Marangoni‐flow induces crater‐like via hole structure of PTAA at the middle layer. In situ measurement of (ultraviolet–visible) UV–vis absorption spectra and computational calculation reveal kinetics of liquid–solid–crystal transition in relation to the functional groups of soluble acene. Interestingly, flow driven hole structure of PTAA in diF–TES ADT/PTAA blend film allows the target NO2 gas to selectively penetrate the channel region, thereby enhancing sensitivity toward NO2, while decreasing affinity with other gases. The results provide protocols for fabricating highlperformance field‐effect transistors and gas sensors in a blending system.

Microstructural Control of Soluble Acene Crystals for Field-Effect Transistor Gas Sensors.

Microstructural control during the solution processing of small-molecule semiconductors (namely, soluble acene) is important for enhancing the performance of field-effect transistors (FET) and sensors. This focused review introduces strategies to enhance the gas-sensing properties (sensitivity, recovery, selectivity, and stability) of soluble acene FET sensors by considering their sensing mechanism. Defects, such as grain boundaries and crystal edges, provide diffusion pathways for target gas molecules to reach the semiconductor-dielectric interface, thereby enhancing sensitivity and recovery. Representative studies on grain boundary engineering, patterning, and pore generation in the formation of soluble acene crystals are reviewed. The phase separation and microstructure of soluble acene/polymer blends for enhancing gas-sensing performance are also reviewed. Finally, flexible gas sensors using soluble acenes and soluble acene/polymer blends are introduced, and future research perspectives in this field are suggested.

1D versus 2D Growth of Soluble Acene Crystals from Soluble Acene/Polymer Blends Governed by a Residual Solvent Reservoir in a Phase‐Separated Polymer Matrix

AbstractThe growth mechanism of soluble acene is highly dependent on the remaining residual solvent following solution processing. The relationship between the amount of residual solvent and the growth modes of a prototypical soluble acene, 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene) are examined under spin casting TIPS‐pentacene/insulating polymer blends. Changing spin time of the blend solution allows to control the amount of residual solvent, which significantly determines the growth modes of TIPS‐pentacene vertically segregated onto the insulating polymer. In situ observation of crystal growth reveals that excess residual solvent in short spin time induces a convective flow in a drying droplet, thereby resulting in 1D growth of TIPS‐pentacene crystals. On the other hand, optimal amount of residual solvent in a moderate spin time results in 2D growth of TIPS‐pentacene crystals. The well‐developed 2D spherulites allow for higher field‐effect mobility than that of the 1D crystals because of the higher perfectness and coverage of TIPS‐pentacene crystals. The use of other types of soluble acene and insulating polymer only changes the kinetics of crystallization, while the transition of growth mode from 1D to 2D is still observed. This general growth mechanism facilitates the understanding of crystallization behavior of soluble acene for the development of high‐performance organic transistors.

Direct printing of soluble acene crystal stripes by a programmed dip-coating process for organic field-effect transistor applications

High-crystalline TIPS-PEN crystal stripes are directly printed with controllable inter-stripe spacingviaprogrammed dip-coating for application in organic field-effect transistors.

Strategies for the Synthesis of Higher Acenes.

The outstanding performance of pentacene‐based molecules in molecular electronics, as well as the predicted enhanced semiconducting properties of extended acenes, have stimulated the development of new synthetic methods and functionalization strategies for the preparation of stable and soluble acenes larger than tetracene with the aim of obtaining improved functional materials.

Dense Assembly of Soluble Acene Crystal Ribbons and Its Application to Organic Transistors.

The preparation of uniform large-area highly crystalline organic semiconductor single crystals remains a challenge in the field of organic field-effect transistors (OFETs). Crystal densities in the channel regions of OFETs have not yet reached sufficiently high values to provide efficient charge transport, and improving channel crystal densities remains an important research area. Herein we fabricated densely well-aligned single crystal arrays of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS_PEN) semiconductor using a straightforward scooping-up (SU) methodology to quickly produce a large-area self-assembled semiconductor crystal layer. The resulting crystalline TIPS_PEN strip arrays obtained using the SU method revealed a packing density that was 2.76 times the value obtained from the dip-coated channel, and the mean interspatial distance between the crystal strips decreased from 21.5 to 7.8 μm. The higher crystal packing density provided efficient charge transport in the FET devices and directly yielded field-effect mobilities as high as 2.16 cm(2)/(V s). These field-effect mobilities were more than three times the values obtained from the OFETs prepared using dip-coated channels. Furthermore, the contact resistance between the source/drain electrodes and the TIPS_PEN crystals decreased by a factor of 2. These contributions represent a significant step forward in improving semiconductor crystal alignment for the fabrication of large-area high-performance organic electronics.

Electrospray-processed soluble acenes toward the realization of high-performance field-effect transistors.

Functionalized acenes have proven to be promising compounds in the field of molecular electronics because of their unique features in terms of the stability, performance, and ease of processing. The emerging concept of large-area-compatible techniques for flexible electronics has brought about a wide variety of well-established techniques for the deposition of soluble acenes, with spray-coating representing an especially fruitful approach. In the present study, electrostatic spray deposition is proposed as an alternative to the conventional spray-coating processes, toward the realization of high-performance organic field-effect transistors (OFETs), on both rigid and flexible substrates. Particularly, a thorough study on the effect of the solvent and spraying regime on the resulting crystalline film's morphology is performed. By optimization of the process conditions in terms of control over the size as well as the crystallization scheme of the droplets, desirable morphological features along with high-quality crystal domains are obtained. The fabricated OFETs exhibit excellent electrical characteristics, with high field-effect mobility up to 0.78 cm(2)/(V s), I(on)/I(off) >10(4), and near-zero threshold voltages. Additionally, the good performance of the OFETs realized on plastic substrates gives great potentiality to the proposed method for applications in the challenging field of large-area electronics.

Aromatic Homologation by Non‐Chelate‐Assisted RhIII‐Catalyzed CH Functionalization of Arenes with Alkynes

Larger condensed arenes are of interest owing to their electro- and photochemical properties. An efficient synthesis is the catalyzed aromatic annulation of a smaller arene with two alkyne molecules. Besides difunctionalized starting materials, directed C-H functionalization can be used for such aromatic homologation. However, thus far the requirement of either pre-functionalized substrates or suitable directing groups were limiting this approach. Herein, we describe a rhodium(III)-catalyzed method allowing the use of completely unbiased arenes and internal alkynes. The reaction works best with copper(II) 2-ethylhexanoate and decabromodiphenyl ether as the oxidant combination. This aromatic annulation tolerates a variety of functional groups and delivers homologated condensed arenes. Aside from simple benzenes, naphthalenes and higher condensed arenes provide access to highly substituted and highly soluble acenes structures having important electronic and photophysical properties.

High-Performance Triethylsilylethynyl Anthradithiophene Transistors Prepared without Solvent Vapor Annealing: The Effects of Self-Assembly during Dip-Coating

Solution-processable small-molecule organic semiconductors have recently attracted significant attention for use as the active channel layers in organic field-effect transistors due to their good intrinsic charge carrier mobility and easy processability. Dip-coating is a good method for optimizing the film morphology and molecular ordering of the small-molecular semiconductors because the drying speed can be quantitatively controlled at the air-solution-substrate contact line. Here, we report the preparation of highly crystalline triethylsilylethynyl-anthradithiophene (TES-ADT) crystal arrays that exhibit an excellent field-effect mobility (up to 1.8 cm(2)/(V s)) via an optimized one-step dip-coating process. High-quality TES-ADT crystals were grown without solvent vapor annealing postprocessing steps, which were previously thought to be essential for improving the morphology, crystallinity, and electrical characteristics of TES-ADT thin films. An interesting correlation between the optimal pull-out rate and the self-assembly tendencies of some soluble acene semiconductors was observed, and the origin of the correlation was investigated. Our work demonstrates an alternative simple approach to achieving highly crystalline TES-ADT thin films, and further proposes a prospective method for optimizing the formation of thin films via the molecular self-assembly of soluble acenes.

고분자/무기 하이브리드 절연막을 이용한 용액공정용 저분자 박막트랜지스터의 안정성 향상 연구

Solution-processed small molecular semiconductors (soluble acenes) serve as ideal active materials for high-performance, printed organic thin-film transistors (OTFTs). However, device stability of soluble acene TFTs has not been intensively studied. Here, we showed that device stability of soluble acene TFTs can be significantly enhanced by the use of polymer/inorganic hybrid gate-dielectrics. Triethylsilylethynyl-anthradithiophene (TES-ADT) TFTs fabricated on polystyrene (PS)/ hybrid gate dielectrics exhibited high performance such as high field-effect mobility () and on-off current ratio (). In addition, transfer characteristic of the TFTs did not shift under the prolonged gate-bias (8000s). This outstanding device stability is due to the device structure which consists of highly crystalline TES-ADT crystals and trap-free PS/ dielectric.

Synthesis and Structure Characterization of a Stable Nonatwistacene

A clean reaction strategy based on thermally eliminating lactam bridges from a soluble acene precursor through a retro-Diels–Alder reaction, led to the synthesis and characterization of a novel, stable, green crystalline 6,8,10,17,19,21-hexaphenyl-1.22,4.5,11.12,15.16-tetrabenzononatwistacene. An analysis of the single crystal structure of the nonatwistacene indicates that this molecule is twisted at an angle of 25.44°.

Highly Crystalline Soluble Acene Crystal Arrays for Organic Transistors: Mechanism of Crystal Growth During Dip‐Coating

AbstractThe preparation of uniform large‐area highly crystalline organic semiconductor thin films that show outstanding carrier mobilities remains a challenge in the field of organic electronics, including organic field‐effect transistors. Quantitative control over the drying speed during dip‐coating permits optimization of the organic semiconductor film formation, although the kinetics of crystallization at the air–solution–substrate contact line are still not well understood. Here, we report the facile one‐step growth of self‐aligning, highly crystalline soluble acene crystal arrays that exhibit excellent field‐effect mobilities (up to 1.5 cm V−1 s−1) via an optimized dip‐coating process. We discover that optimized acene crystals grew at a particular substrate lifting‐rate in the presence of low boiling point solvents, such as dichloromethane (b.p. of 40.0 °C) or chloroform (b.p. of 60.4 °C). Variable‐temperature dip‐coating experiments using various solvents and lift rates are performed to elucidate the crystallization behavior. This bottom‐up study of soluble acene crystal growth during dip‐coating provides conditions under which one may obtain uniform organic semiconductor crystal arrays with high crystallinity and mobilities over large substrate areas, regardless of the substrate geometry (wafer substrates or cylinder‐shaped substrates).

Effect of Acene Length on Electronic Properties in 5‐, 6‐, and 7‐Ringed Heteroacenes

Three novel soluble acene derivatives consisting of the same functional group but varying in backbone size were characterized for their structural and electrical properties. An increase in acene length was found to directly contribute to more favourable packing schemes for hole transport, leading to field-effect mobilities of 1.8 cm2V−1s−1 for difluoro tri-sec-butylsilylethynyl pentacenedithiophene, the longest derivative.

Controlled Deposition of Highly Ordered Soluble Acene Thin Films: Effect of Morphology and Crystal Orientation on Transistor Performance

Controlling the morphology of soluble small molecule organic semiconductors is crucial for the application of such materials in electronic devices. Using a simple dip-coating process we systematically vary the film drying speed to produce a range of morphologies, including oriented needle-like crystals. Structural characterization as well as electrical transistor measurements show that intermediate drying velocities produce the most uniformly aligned films.

Control of the Morphology and Structural Development of Solution‐Processed Functionalized Acenes for High‐Performance Organic Transistors

AbstractSolution‐processable functionalized acenes have received special attention as promising organic semiconductors in recent years because of their superior intermolecular interactions and solution‐processability, and provide useful benchmarks for organic field‐effect transistors (OFETs). Charge‐carrier transport in organic semiconductor thin films is governed by their morphologies and molecular orientation, so self‐assembly of these functionalized acenes during solution processing is an important challenge. This article discusses the charge‐carrier transport characteristics of solution‐processed functionalized acene transistors and, in particular, focuses on the fine control of the films' morphologies and structural evolution during film‐deposition processes such as inkjet printing and post‐deposition annealing. We discuss strategies for controlling morphologies and crystalline microstructure of soluble acenes with a view to fabricating high‐performance OFETs.

Change of molecular ordering in soluble acenes via solvent annealing and its effect on field-effect mobility

The increase of the molecular ordering and field-effect mobility in triethylsilylethynyl anthradithiophene (TES ADT) thin film transistors by solvent annealing was investigated. X-ray diffraction data revealed that TES ADT molecules crystallize with silyl groups on the substrate surface. After solvent annealing, spherulites were formed and the field-effect mobilities dramatically increased up to 0.43cm2∕Vs (over 100-fold) as result of maximized overlap of π electron clouds along the in-plane direction and the formation of a continuous crystal.

Highly soluble acenes as semiconductors for thin film transistors

Acene derivatives 3, 5, 7 and 9 bearing two trimethoxyphenylethynyl substituents have been synthesized. The optical properties of these acenes have been investigated by UV/Vis and fluorescence spectroscopy and their eletrochemical properties have been elucidated by cyclic voltammetry (CV). X-Ray analysis of the anthracene and tetracene derivatives 3 and 5 has revealed a 1-D π-stacking in crystals of 3 and 5. In contrast to their parent hydrocarbons, the present disubstituted acenes are highly soluble in different solvents. Spin-coating has afforded amorphous thin films that exhibit field effect mobility. Best performance has been achieved for the OTFTs prepared from the pentacene derivative 7 with a field effect mobility of 1.9 × 10−5 cm2 V−1 s−1 and an on/off ratio of 103.