Opportunity of Patterning in Chemistry

Patterning offers an efficient way to quantitatively enhance and enlarge material properties and functionalities, offering unprecedented opportunities for innovation in various scientific domains. By precisely controlling the spatial arrangement of materials at the micro- and nanoscale, patterning enables the exploitation of inherent material properties in novel ways. In addition, it generates new properties, leading to the development of advanced devices and applications. This article highlights the significant contributions of spatially controlled patterning in chemistry, particularly in generating new functional properties and devices, discussing some representative articles. Examples include the use of unconventional patterning techniques for surface functionalization, as well as the application of spatial confinement in improving material properties and controlling crystallization processes. Furthermore, the discussion extends to creating new devices, such as optical storage media and sensors, through spatial organization of materials.

Pentacoordinate Cobalt(II) Single Ion Magnets with Pendant Alkyl Chains: Shall We Go for Chloride or Bromide?

Four pentacoordinate complexes 1-4 of the type [Co(L1)X2] and [Co(L2)X2] (where L1=2,6-bis(1-octyl-1H-benzimidazol-2-yl)pyridine for 1 and 2, L2=2,6-bis(1-dodecyl-1H-benzimidazol -2-yl)-pyridine for 3 and 4; X = Cl- for 1 and 3, X...

Supramolecular Assembly of Thiophene-Based Oligomers into Nanostructured Fluorescent Conductive and Chiral Microfibers

The implementation of nano/microelectronic devices requires efficient strategies for the realization of supramolecular structures with desired function and supported on appropriate substrates. This article illustrates a strategy based on the synthesis of thiophene oligomers having the same "sulfur-overrich" quaterthiophene inner core (non bonding interactional algorithm) and different terminal groups. Nano/microfibers are formed on surfaces having a morphology independent of the nature of the deposition substrate and displaying a wide tuning of properties that make the fibers optoelectronically suitable for application in devices.

Thermodynamically versus Kinetically Controlled Self-Assembly of a Naphthalenediimide-Thiophene Derivative: From Crystalline, Fluorescent, n-Type Semiconducting 1D Needles to Nanofibers

The control over aggregation pathways is a key requirement for present and future technologies, as it can provide access to a variety of sophisticated structures with unique functional properties. In this work, we demonstrate an unprecedented control over the supramolecular self-assembly of a semiconductive material, based on a naphthalenediimide core functionalized with phenyl-thiophene moieties at the imide termini, by trapping the molecules into different arrangements depending on the crystallization conditions. The control of the solvent evaporation rate enables the growth of highly elaborated hierarchical self-assembled structures: either in an energy-minimum thermodynamic state when the solvent is slowly evaporated forming needle-shaped crystals (polymorph α) or in a local energy-minimum state when the solvent is rapidly evaporated leading to the formation of nanofibers (polymorph β). The exceptional persistence of the kinetically trapped β form allowed the study and comparison of its characteristics with that of the stable α form, revealing the importance of molecular aggregation geometry in functional properties. Intriguingly, we found that compared to the thermodynamically stable α phase, characterized by a J-type aggregation, the β phase exhibits (i) an unusual strong blue shift of the emission from the charge-transfer state responsible for the solid-state luminescent enhancement, (ii) a higher work function with a "rigid shift" of the electronic levels, as shown by Kelvin probe force microscopy and cyclic voltammetry measurements, and (iii) a superior field-effect transistor mobility in agreement with an H-type aggregation as indicated by X-ray analysis and theoretical calculations.

Multifunctional self-assembled monolayers via microcontact printing and degas-driven flow guided patterning

Soft lithography-based patterning techniques have been developed to investigate biological and chemical phenomena. Until now, micropatterning with various materials required multiple procedural steps such as repeating layer-by-layer patterning, aligning of stamps, and incubating printed inks. Herein, we describe a facile micropatterning method for producing chemically well-defined surface architectures by combining microcontact (µCP) and microfluidic vacuum-assisted degas-driven flow guided patterning (DFGP) with a poly(dimethylsiloxane) (PDMS) stamp. To demonstrate our concept, we fabricated a bi-composite micropatterned surface with different functional molecular inks such as fluorescein isothiocyanate labelled bovine serum albumin (FITC-BSA) and polyethylene glycol (PEG)-silane for a biomolecule array, and 3-aminopropyltriethoxysilane (APTES) and PEG-silane pattern for a self-assembled colloid gold nanoparticle monolayer. With a certain composition of molecular inks for the patterning, bi-composite surface patterns could be produced by this µCP-DFGP approach without any supplementary process. This patterning approach can be used in microfabrication and highly applicable to biomolecules and nanoparticles that spread as a monolayer.

Nanocylindrical confinement imparts highest structural order in molecular self-assembly of organophosphonates on aluminum oxide

We report the impact of geometrical constraint on intramolecular interactions in self-assembled monolayers (SAMs) of alkylphosphonates grown on anodically oxidized aluminum (AAO). Molecular order in these films was determined by sum frequency generation (SFG) spectroscopy, a more sensitive measure of order than infrared absorption spectroscopy. Using SFG we show that films grown on AAO are, within detection limits, nearly perfectly ordered in an all-trans alkyl chain configuration. In marked contrast, films formed on planar, plasma-oxidized aluminum oxide or α-Al₂O₃ (0001) are replete with gauche defects. We attribute these differences to the nanocylindrical structure of AAO, which enforces molecular confinement.

High-Performance Phototransistors Based on PDIF-CN2 Solution-Processed Single Fiber and Multifiber Assembly

Here we describe the fabrication of organic phototransistors based on either single or multifibers integrated in three-terminal devices. These self-assembled fibers have been produced by solvent-induced precipitation of an air stable and solution-processable perylene di-imide derivative, i.e., PDIF-CN2. The optoelectronic properties of these devices were compared to devices incorporating more disordered spin-coated PDIF-CN2 thin-films. The single-fiber devices revealed significantly higher field-effect mobilities, compared to multifiber and thin-films, exceeding 2 cm(2) V(-1) s(-1). Such an efficient charge transport is the result of strong intermolecular coupling between closely packed PDIF-CN2 molecules and of a low density of structural defects. The improved crystallinity allows efficient collection of photogenerated Frenkel excitons, which results in the highest reported responsivity (R) for single-fiber PDI-based phototransistors, and photosensitivity (P) exceeding 2 × 10(3) AW(-1), and 5 × 10(3), respectively. These findings provide unambiguous evidence for the key role played by the high degree of order at the supramolecular level to leverage the material's properties toward the fabrication of light-sensitive organic field-effect transistors combining a good operational stability, high responsivity and photosensitivity. Our results show also that the air-stability performances are superior in devices where highly crystalline supramolecularly engineered architectures serve as the active layer.

Hierarchical Micro/Nano Structures by Combined Self-Organized Dewetting and Photopatterning of Photoresist Thin Films

Photoresists are the materials of choice for micro/nanopatterning and device fabrication but are rarely used as a self-assembly material. We report for the first time a novel interplay of self-assembly and photolithography for fabrication of hierarchical and ordered micro/nano structures. We create self-organized structures by the intensified dewetting of unstable thin (∼10 nm to 1 μm) photoresist films by annealing them in an optimal solvent and nonsolvent liquid mixture that allows spontaneous dewetting to form micro/nano smooth dome-like structures. The density, size (∼100 nm to millimeters), and curvature/contact angle of the dome/droplet structures are controlled by the film thickness, composition of the dewetting liquid, and time of annealing. Ordered dewetted structures are obtained simply by creating spatial variation of viscosity by ultraviolet exposure or by photopatterning before dewetting. Further, the structures thus fabricated are readily photopatterned again on the finer length scales after dewetting. We illustrate the approach by fabricating several three-dimensional structures of varying complexity with secondary and tertiary features.

Supramolecular oligothiophene microfibers spontaneously assembled on surfaces or coassembled with proteins inside live cells

During the last few decades, multifunctional nano- and microfibers made of semiconducting π-conjugated oligomers and polymers have generated much interest because of a broad range of applications extending from sensing to bioelectronic devices and (opto)electronics. The simplest technique for the fabrication of these anisotropic supramolecular structures is to let the molecules do the work by spontaneous organization driven by the information encoded in their molecular structure. Oligothiophenes-semiconducting and fluorescent compounds that have been extensively investigated for applications in thin-film field-effect transistors and solar cells and to a lesser extent as dyes for fluorescent labeling of proteins, DNA, and live cells-are particularly suited as building blocks for supramolecular architectures because of the peculiar properties of the thiophene ring. Because of the great polarizability of sulfur outer-shell electrons and the consequent facile geometric deformability and adaptability of the ring to the environment, thiophene can generate multiple nonbonding interactions to promote non-covalent connections between blocks. Furthermore, sulfur can be hypervalent, i.e., it can accommodate more than the eight electrons normally associated with s and p shells. Hypervalent oligothiophene-S,S-dioxides whose oxygen atoms can be involved in hydrogen bonding have been synthesized. These compounds are amphiphilic, and some of them are able to spontaneously cross the membrane of live cells. Hypervalent nonbonding interactions of divalent sulfur, defined as weak coordination to a proximate nitrogen or oxygen, have also been invoked in the solid-state packing of many organic molecules and in the architecture of proteins. In this Account, we describe two different types of thiophene-based building blocks that can induce the spontaneous formation of nanostructured microfibers in very different environments. The first, based on the synthesis of "sulfur-overrich" hexamers and octamers, leads to surface-independent self-assembly of microfibers-helical or rodlike depending on the groups attached to the same identical inner core-that are crystalline, fluorescent, and conductive and display chirality despite the lack of chiral carbon atoms on the building blocks. Supramolecular polymorphic microfibers are also formed, and they are characterized by very different functional properties. The second, based on a rigid oligothiophene-S,S-dioxide, leads to coassembled protein-oligothiophene microfibers that are physiologically formed inside live cells. The oligothiophene-S,S-dioxide can indeed spontaneously cross the membrane of live cells and be directed toward the perinuclear region, where it is recognized and incorporated by specific peptides during the formation of fibrillar proteins without being harmful to the cells. Coassembled oligothiophene-protein microfibers are progressively formed through a cell-mediated physiological process. Thanks to the oligothiophene blocks, the microfibers possess fluorescence and charge-conduction properties. By means of fluorescence imaging, we demonstrated that various types of live cells seeded on these microfibers were able to internalize and degrade them, experiencing in turn different effects on their morphology and viability, suggesting a possible use of the microfibers as multiscale biomaterials to direct cell behavior. On the whole, our results show the great versatility of oligothiophene building blocks and allow us to foresee that their capabilities of spontaneous assembly in the most different environments could be exploited in much more exciting research fields than those explored to date.

Self-organization of functional materials in confinement

This Account aims to describe our experience in the use of patterning techniques for addressing the self-organization processes of materials into spatially confined regions on technologically relevant surfaces. Functional properties of materials depend on their chemical structure, their assembly, and spatial distribution at the solid state; the combination of these factors determines their properties and their technological applications. In fact, by controlling the assembly processes and the spatial distribution of the resulting structures, functional materials can be guided to technological and specific applications. We considered the principal self-organizing processes, such as crystallization, dewetting and phase segregation. Usually, these phenomena produce defective molecular films, compromising their use in many technological applications. This issue can be overcome by using patterning techniques, which induce molecules to self-organize into well-defined patterned structures, by means of spatial confinement. In particular, we focus our attention on the confinement effect achieved by stamp-assisted deposition for controlling size, density, and positions of material assemblies, giving them new chemical/physical functionalities. We review the methods and principles of the stamp-assisted spatial confinement and we discuss how they can be advantageously exploited to control crystalline order/orientation, dewetting phenomena, and spontaneous phase segregation. Moreover, we highlight how physical/chemical properties of soluble functional materials can be driven in constructive ways, by integrating them into operating technological devices.

Oligothiophene semiconductors: synthesis, characterization, and applications for organic devices

Oligothiophenes provide a highly controlled and adaptable platform to explore various synthetic, morphologic, and electronic relationships in organic semiconductor systems. These short-chain systems serve as models for establishing valuable structure-property relationships to their polymer analogs. In contrast to their polymer counterparts, oligothiophenes afford high-purity and well-defined materials that can be easily modified with a variety of functional groups. Recent work by a number of research groups has revealed functionalized oligothiophenes to be the up-and-coming generation of advanced materials for organic electronic devices. In this review, we discuss the synthesis and characterization of linear oligothiophenes with a focus on applications in organic field effect transistors and organic photovoltaics. We will highlight key structural parameters, such as crystal packing, intermolecular interactions, polymorphism, and energy levels, which in turn define the device performance.

Logic-gate devices based on printed polymer semiconducting nanostripes

The applications of organic semiconductors in complex circuitry such as printed CMOS-like logic circuits demand miniaturization of the active structures to the submicrometric and nanoscale level while enhancing or at least preserving the charge transport properties upon processing. Here, we addressed this issue by using a wet lithographic technique, which exploits and enhances the molecular order in polymers by spatial confinement, to fabricate ambipolar organic field effect transistors and inverter circuits based on nanostructured single component ambipolar polymeric semiconductor. In our devices, the current flows through a precisely defined array of nanostripes made of a highly ordered diketopyrrolopyrrole-benzothiadiazole copolymer with high charge carrier mobility (1.45 cm(2) V(-1) s(-1) for electrons and 0.70 cm(2) V(-1) s(-1) for holes). Finally, we demonstrated the functionality of the ambipolar nanostripe transistors by assembling them into an inverter circuit that exhibits a gain (105) comparable to inverters based on single crystal semiconductors.