Direct-ink-write cross-linkable bottlebrush block copolymers for on-the-fly control of structural color.

Additive manufacturing capable of controlling and dynamically modulating structures down to the nanoscopic scale remains challenging. By marrying additive manufacturing with self-assembly, we develop a UV (ultra-violet)-assisted direct ink write approach for on-the-fly modulation of structural color by programming the assembly kinetics through photo-cross-linking. We design a photo-cross-linkable bottlebrush block copolymer solution as a printing ink that exhibits vibrant structural color (i.e., photonic properties) due to the nanoscopic lamellar structures formed post extrusion. By dynamically modulating UV-light irradiance during printing, we can program the color of the printed material to access a broad spectrum of visible light with a single ink while also creating color gradients not previously possible. We unveil the mechanism of this approach using a combination of coarse-grained simulations, rheological measurements, and structural characterizations. Central to the assembly mechanism is the matching of the cross-linking timescale with the assembly timescale, which leads to kinetic trapping of the assembly process that evolves structural color from blue to red driven by solvent evaporation. This strategy of integrating cross-linking chemistry and out-of-equilibrium processing opens an avenue for spatiotemporal control of self-assembled nanostructures during additive manufacturing.

Inverse chirality-induced spin selectivity effect in chiral assemblies of π-conjugated polymers.

Coupling of spin and charge currents to structural chirality in non-magnetic materials, known as chirality-induced spin selectivity, is promising for application in spintronic devices at room temperature. Although the chirality-induced spin selectivity effect has been identified in various chiral materials, its Onsager reciprocal process, the inverse chirality-induced spin selectivity effect, remains unexplored. Here we report the observation of the inverse chirality-induced spin selectivity effect in chiral assemblies of π-conjugated polymers. Using spin-pumping techniques, the inverse chirality-induced spin selectivity effect enables quantification of the magnitude of the longitudinal spin-to-charge conversion driven by chirality-induced spin selectivity in different chiral polymers. By widely tuning conductivities and supramolecular chiral structures via a printing method, we found a very long spin relaxation time of up to several nanoseconds parallel to the chiral axis. Our demonstration of the inverse chirality-induced spin selectivity effect suggests possibilities for elucidating the puzzling interplay between spin and chirality, and opens a route for spintronic applications using printable chiral assemblies.

From Solution to Thin Film: Molecular Assembly of π-Conjugated Systems and Impact on (Opto)electronic Properties.

The assembly of conjugated organic molecules from solution to solid-state plays a critical role in determining the thin film morphology and optoelectronic properties of solution-processed organic electronics and photovoltaics. During evaporative solution processing, π-conjugated systems can assemble via various forms of intermolecular interactions, forming distinct aggregate structures that can drastically tune the charge transport landscape in the solid-state. In blend systems composed of donor polymer and acceptor molecules, assembly of neat materials couples with phase separation and crystallization processes, leading to complex phase transition pathways which govern the blend film morphology. In this review, we provide an in-depth review of molecular assembly processes in neat conjugated polymers and nonfullerene small molecule acceptors and discuss their impact on the thin film morphology and optoelectronic properties. We then shift our focus to blend systems relevant to organic solar cells and discuss the fundamentals of phase transition and highlight how the assembly of neat materials and processing conditions can affect blend morphology and device performance.

Mechanical properties and peculiarities of molecular crystals.

In the last century, molecular crystals functioned predominantly as a means for determining the molecular structures via X-ray diffraction, albeit as the century came to a close the response of molecular crystals to electric, magnetic, and light fields revealed that the physical properties of molecular crystals were as rich as the diversity of molecules themselves. In this century, the mechanical properties of molecular crystals have continued to enhance our understanding of the colligative responses of weakly bound molecules to internal frustration and applied forces. Here, the authors review the main themes of research that have developed in recent decades, prefaced by an overview of the particular considerations that distinguish molecular crystals from traditional materials such as metals and ceramics. Many molecular crystals will deform themselves as they grow under some conditions. Whether they respond to intrinsic stress or external forces or interactions among the fields of growing crystals remains an open question. Photoreactivity in single crystals has been a leading theme in organic solid-state chemistry; however, the focus of research has been traditionally on reaction stereo- and regio-specificity. However, as light-induced chemistry builds stress in crystals anisotropically, all types of motions can be actuated. The correlation between photochemistry and the responses of single crystals-jumping, twisting, fracturing, delaminating, rocking, and rolling-has become a well-defined field of research in its own right: photomechanics. The advancement of our understanding requires theoretical and high-performance computations. Computational crystallography not only supports interpretations of mechanical responses, but predicts the responses itself. This requires the engagement of classical force-field based molecular dynamics simulations, density functional theory-based approaches, and the use of machine learning to divine patterns to which algorithms can be better suited than people. The integration of mechanics with the transport of electrons and photons is considered for practical applications in flexible organic electronics and photonics. Dynamic crystals that respond rapidly and reversibly to heat and light can function as switches and actuators. Progress in identifying efficient shape-shifting crystals is also discussed. Finally, the importance of mechanical properties to milling and tableting of pharmaceuticals in an industry still dominated by active ingredients composed of small molecule crystals is reviewed. A dearth of data on the strength, hardness, Young's modulus, and fracture toughness of molecular crystals underscores the need for refinement of measurement techniques and conceptual tools. The need for benchmark data is emphasized throughout.

Role of Interfacial Interactions in the Graphene-Directed Assembly of Monolayer Conjugated Polymers.

Development of graphene-organic hybrid electronics is one of the most promising directions for next-generation electronic materials. However, it remains challenging to understand the graphene-organic semiconductor interactions right at the interface, which is key to designing hybrid electronics. Herein, we study the influence of graphene on the multiscale morphology of solution-processed monolayers of conjugated polymers (PII-2T, DPP-BTz, DPP2T-TT, and DPP-T-TMS). The strong interaction between graphene and PII-2T was manifested in the high fiber density and high film coverage of monolayer films deposited on graphene compared to plasma SiO2 substrates. The monolayer films on graphene also exhibited a higher relative degree of crystallinity and dichroic ratio or polymer alignment, i.e., higher degree of order. Raman spectroscopy revealed the increased backbone planarity of the conjugated polymers upon deposition on graphene as well as the existence of electronic interaction across the interface. This speculation was further substantiated by the results of photoelectron spectroscopy (XPS and UPS) of PII-2T, which showed a decrease in binding energy of several atomic energy levels, movement of the Fermi level toward HOMO, and an increase in work function, all of which indicate p-doping of the polymer. Our results provide a new level of understanding on graphene-polymer interactions at nanoscopic interfaces and the consequent impact on multiscale morphology, which will aid in the design of efficient graphene-organic hybrid electronics.

Rapid, interface-driven domain orientation in bottlebrush diblock copolymer films during thermal annealing.

Favorable polymer-substrate interactions induce surface orientation fields in block copolymer (BCP) melts. In linear BCP processed near equilibrium, alignment of domains generally persists for a small number of periods (∼4-6 D0) before randomization of domain orientation. Bottlebrush BCP are an emerging class of materials with distinct chain dynamics stemming from substantial molecular rigidity, enabling rapid assembly at ultrahigh (>100 nm) domain periodicities with strong photonic properties (structural color). This work assesses interface-induced ordering in PS-b-PLA bottlebrush diblock copolymer films during thermal annealing between planar surfaces. To clearly observe the decay in orientational order from surface to bulk, we choose to study micron-scale films spanning greater than 200 lamellar periods. In situ optical microscopy and transmission UV-Vis spectroscopy are used to monitor photonic properties during annealing and paired with ex situ UV-Vis reflection measurement, cross-sectional scanning electron microscopy (SEM), and small-angle X-ray scattering (SAXS) to probe the evolution of domain microstructure. Photonic properties were observed to saturate within minutes of annealing at 150 °C, with distinct variation in transmission response as a function of film thickness. The depth of the highly aligned surface region was found to vary stochastically in the range of 30-100 lamellar periods, with the sharpness of the orientation gradient decreasing substantially with increasing film thickness. This observation suggests a competition between growth of aligned, heterogeneously nucleated, grains at the surface and orientationally isotropic, homogeneously nucleated, grains throughout the bulk. This work demonstrates the high potential of bottlebrush block copolymers in rapid fabrication workflows and provides a point of comparison for future application of directed self-assembly to BBCP ordering.

Three-Dimensional Printable Nanoporous Polymer Matrix Composites for Daytime Radiative Cooling.

Daytime radiative cooling presents an exciting new strategy for combating global warming, because it can passively cool buildings by reflecting sunlight and utilizing the infrared atmospheric window to eject heat into outer space. Recent progress with novel material designs showed promising subambient cooling performance under direct sunlight. However, large-scale implementation of radiative cooling technologies is still limited by the high-cost and complex fabrication. Here, we develop a nanoporous polymer matrix composite (PMC) to enable rapid production and cost reduction using commercially available polymer processing techniques, such as molding, extrusion, and 3D printing. With a high solar reflectance of 96.2% and infrared emissivity > 90%, the nanoporous PMC achieved a subambient temperature drop of 6.1 °C and cooling power of 85 W/m2 under direct sunlight, which are comparable to the state-of-the-art. This work offers great promise to make radiative cooling technologies more viable for saving energy and reducing emissions in building cooling applications.

Identification and Allele Combination Analysis of Rice Grain Shape-Related Genes by Genome-Wide Association Study.

Grain shape is an important agronomic character of rice, which affects the appearance, processing, and the edible quality. Screening and identifying more new genes associated with grain shape is beneficial to further understanding the genetic basis of grain shape and provides more gene resources for genetic breeding. This study has a natural population containing 623 indica rice cultivars. Genome-wide association studies/GWAS of several traits related to grain shape (grain length/GL, grain width/GW, grain length to width ratio/GLWR, grain circumferences/GC, and grain size/grain area/GS) were conducted by combining phenotypic data from four environments and the second-generation resequencing data, which have identified 39 important Quantitative trait locus/QTLs. We analyzed the 39 QTLs using three methods: gene-based association analysis, haplotype analysis, and functional annotation and identified three cloned genes (GS3, GW5, OsDER1) and seven new candidate genes in the candidate interval. At the same time, to effectively utilize the genes in the grain shape-related gene bank, we have also analyzed the allelic combinations of the three cloned genes. Finally, the extreme allele combination corresponding to each trait was found through statistical analysis. This study's novel candidate genes and allele combinations will provide a valuable reference for future breeding work.

Modulation of π-stacking modes and photophysical properties of an organic semiconductor through isosteric cocrystallization.

We report on the control of π-stacking modes (herringbone vs slipped-stack) and photophysical properties of 9,10-bis((E)-2-(pyridin-4-yl)vinyl)anthracene (BP4VA), an anthracene-based organic semiconductor (OSC), by isosteric cocrystallization (i.e., the replacement of one functional group in a coformer with another of "similar" electronic structure) with 2,4,6-trihalophenols (3X-ph-OH, where X = Cl, Br, and I). Specifically, BP4VA organizes as slipped-stacks when cocrystallized with 3Cl-ph-OH and 3Br-ph-OH, while cocrystallization with 3I-ph-OH results in a herringbone mode. The photoluminescence and molecular frontier orbital energy levels of BP4VA were effectively modulated by the presence of 3X-ph-OH through cocrystallization. We envisage that the cocrystallization of OSCs with minimal changes in cocrystal formers can provide access to convenient structural and property diversification for advanced single-crystal electronics.

Martensitic transition in molecular crystals for dynamic functional materials.

Molecular martensitic materials are an emerging class of smart materials with enormous tunability in physicochemical properties, attributed to the tailored molecular and crystal structures through molecular design. This class of materials exhibits ultrafast and reversible structural transitions in response to thermal and mechanical stimuli, which underlies fascinating properties such as thermoelasticity, superelasticity, ferroelasticity, and shape memory effect. These dynamic properties are not widely explored in molecular crystals and therefore molecular martensitic materials represent a new frontier in the field of solid-state chemistry. In martensitic transitions, the materials not only exhibit substantial shape changes but also remember the functions in the associated polymorphic phases. This suggests promising applicability towards light-weight actuators, lifts, dampers, sensors, shape-/function-memory and ultraflexible optoelectronic devices. In this article, we review characteristics, detailed transition mechanisms, and potential applications of molecular martensitic materials. In particular, we aim to describe transition characteristics by collecting cases with similar transition principles in order to glean insights into further advancement of molecular martensitic materials. Overall, we believe that molecular martensitic materials are emerging as the next generation smart materials that have shown promise in advancing a wide range of domains of applications.

Comparative transcriptome analysis and identification of candidate adaptive evolution genes of Miscanthus lutarioriparius and Miscanthus sacchariflorus.

Miscanthus species are perennial C4 grasses that are considered promising energy crops because of their high biomass yields, excellent adaptability and low management costs. Miscanthus lutarioriparius and Miscanthus sacchariflorus are closely related subspecies that are distributed in different habitats. However, there are only a few reports on the mechanisms by which Miscanthus adapts to different environments. Here, comparative transcriptomic and morphological analyses were used to study the evolutionary adaptation of M. lutarioriparius and M. sacchariflorus to different habitats. In total, among 7586 identified orthologs, 2060 orthologs involved in phenylpropanoid biosynthesis and plant hormones were differentially expressed between the two species. Through an analysis of the Ka/Ks ratios of the orthologs, we estimated that the divergence time between the two species was approximately 4.37 Mya. In addition, 37 candidate positively selected orthologs (PSGs) that played important roles in the adaptation of these species to different habitats were identified. Then, the expression levels of 20 PSGs in response to flooding and drought stress were analyzed, and the analysis revealed significant changes in their expression levels. These results facilitate our understanding of the evolutionary adaptation to habitats and the speciation of M. lutarioriparius and M. sacchariflorus. We hypothesise that lignin synthesis genes are the main cause of the morphological differences between the two species. In summary, the plant nonspecific phospholipase C gene family and the receptor-like protein kinase gene family played important roles in the evolution of these two species. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-01030-1.

Comparative population genomics reveals genetic divergence and selection in lotus, Nelumbo nucifera.

BACKGROUND: Lotus (Nelumbo nucifera) is an aquatic plant with important agronomic, horticulture, art and religion values. It was the basal eudicot species occupying a critical phylogenetic position in flowering plants. After the domestication for thousands of years, lotus has differentiated into three cultivated types -flower lotus, seed lotus and rhizome lotus. Although the phenotypic and genetic differentiations based on molecular markers have been reported, the variation on whole-genome level among the different lotus types is still ambiguous. RESULTS: In order to reveal the evolution and domestication characteristics of lotus, a total of 69 lotus accessions were selected, including 45 cultivated accessions, 22 wild sacred lotus accessions, and 2 wild American lotus accessions. With Illumina technology, the genomes of these lotus accessions were resequenced to > 13× raw data coverage. On the basis of these genomic data, 25 million single-nucleotide polymorphisms (SNPs) were identified in lotus. Population analysis showed that the rhizome and seed lotus were monophyletic and genetically homogeneous, whereas the flower lotus was biphyletic and genetically heterogeneous. Using population SNP data, we identified 1214 selected regions in seed lotus, 95 in rhizome lotus, and 37 in flower lotus. Some of the genes in these regions contributed to the essential domestication traits of lotus. The selected genes of seed lotus mainly affected lotus seed weight, size and nutritional quality. While the selected genes were responsible for insect resistance, antibacterial immunity and freezing and heat stress resistance in flower lotus, and improved the size of rhizome in rhizome lotus, respectively. CONCLUSIONS: The genome differentiation and a set of domestication genes were identified from three types of cultivated lotus- flower lotus, seed lotus and rhizome lotus, respectively. Among cultivated lotus, flower lotus showed the greatest variation. The domestication genes may show agronomic importance via enhancing insect resistance, improving seed weight and size, or regulating lotus rhizome size. The domestication history of lotus enhances our knowledge of perennial aquatic crop evolution, and the obtained dataset provides a basis for future genomics-enabled breeding.

A Reversible Structural Phase Transition by Electrochemically-Driven Ion Injection into a Conjugated Polymer.

We find that conjugated polymers can undergo reversible structural phase transitions during electrochemical oxidation and ion injection. We study poly[2,5-bis(thiophenyl)-1,4-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzene] (PB2T-TEG), a conjugated polymer with glycolated side chains. Using grazing incidence wide-angle X-ray scattering (GIWAXS), we show that, in contrast to previously known polymers, this polymer switches between two structurally distinct crystalline phases associated with electrochemical oxidation/reduction in an aqueous electrolyte. Importantly, we show that this unique phase change behavior has important physical consequences for ion-polaron pair transport. Notably, using moving front experiments visualized by both optical microscopy and super-resolution photoinduced force microscopy (PiFM), we show that a laterally propagating ion-polaron pair front in PB2T-TEG exhibits non-Fickian transport, retaining a sharp step-edge profile, in stark contrast to the Fickian diffusion more commonly observed in polymers like P3MEEMT. This structural phase transition is reminiscent of those accompanying ion uptake in inorganic materials like LiFePO4. We propose that the engineering of similar properties in future conjugated polymers may enable the realization of new materials with superior performance in electrochemical energy storage or neuromorphic memory applications.

Super- and Ferroelastic Organic Semiconductors for Ultraflexible Single-Crystal Electronics.

Like silicon, single crystals of organic semiconductors are pursued to attain intrinsic charge transport properties. However, they are intolerant to mechanical deformation, impeding their application in flexible electronic devices. Such contradictory properties, namely exceptional molecular ordering and mechanical flexibility, are unified in this work. We found that bis(triisopropylsilylethynyl)pentacene (TIPS-P) crystals can undergo mechanically induced structural transitions to exhibit superelasticity and ferroelasticity. These properties arise from cooperative and correlated molecular displacements and rotations in response to mechanical stress. By utilizing a bending-induced ferroelastic transition of TIPS-P, flexible single-crystal electronic devices were obtained that can tolerate strains (ϵ) of more than 13 % while maintaining the charge carrier mobility of unstrained crystals (µ>0.7 µ0 ). Our work will pave the way for high-performance ultraflexible single-crystal organic electronics for sensors, memories, and robotic applications.

Silk Fluorescence Collimator for Ultrasensitive Humidity Sensing and Light-Harvesting in Semitransparent Dye-Sensitized Solar Cells.

This work examines the self-collimation effect of silk materials on fluorescence emission/detection. A macroscopic regulation strategy, coupled with meso-reconstruction and meso-functionalization, is adopted to amplify the fluorescence emission of organic fluorescent dyes (i.e., Rhodamine 6G (R6G)) using silk photonic crystal (PC) films. The fluorescence emission can be linearly enhanced or inhibited by a PC as a result of the photonic bandgap coupling with the excitation light and/or emission light. Depending on the design of the silk fluorescence collimator, the emission can reach 49.37 times higher than the control. The silk fluorescence collimator can be applied to achieve significant benefits: for instance, as a humidity sensor, it provides good reproducibility and a sensitivity of 28.50 a.u./% relative humidity, which is 80.78 times higher than the sensitivity of the control, and as a novel curtain, it raises the energy conversion efficiency of the semitransparent dye-sensitized solar cells (DSSCs) by 16%.

Transcriptome, physiological and biochemical analysis of Triarrhena sacchariflora in response to flooding stress.

BACKGROUND: In recent decades, the frequency of flooding is increasing with the change of global climate. Flooding has become one of the major abiotic stresses that seriously affect growth and development of plants. Triarrhena sacchariflora Nakai has been considered a promising energy crop for utilization in ethanol production. Flooding stress is among the most severe abiotic stressors in the production of Nakai. However, the physiological and molecular biological mechanisms of Nakai response to flooding is still unclear. In the present study, in order to understand the molecular mechanisms of Nakai in response to flooding stress, the transcriptome, physiological and biochemical were investigated. RESULTS: The results demonstrated that significant physiological changes were observed in photosynthetic system, antioxidative enzyme activity, chlorophyll, carotenoid, proline, lipid peroxidation and soluble sugar content under normal and flooding treatments. Such as, the chlorophyll, carotenoid contents and photosynthetic system were significantly decreased. Whereas, the antioxidative enzyme activity, proline, lipid peroxidation and soluble sugar has increased first and then decreased under treatments compared with the normal plants. Additionally, a total of 8832, 6608 and 3649 unigenes were validated to be differentially expressed under different treatments, respectively. Besides, gene ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis of the different expression levels of genes also presented processes, which involved in photosynthesis, sucrose catabolism, glycolysis, stress response and defense, phytohormone biosynthesis and signal transduction. CONCLUSIONS: The results provide a comprehensive view of the complex molecular events involved in the response to flooding stress of Nakai leaves, which also will promote the research in the development of flood-resistant crops and provide new tools for Nakai breeders.

Selection of suitable reference genes for quantitive real-time PCR normalization in Miscanthus lutarioriparia.

Miscanthus lutarioriparia, which is found widespread in China, has attracted great attention as a most potential bioenergy plant for years. The quantitative real time PCR (RT-qPCR) has appeared as a sensitive and powerful technique to measure gene expression in living organisms during different development stages. In this study, we evaluated ten candidate genes, including 25S ribosomal RNA gene (25S rRNA), actin1 gene (ACT1), carotenoid-binding protein 20 gene (CBP20), glyceraldehyde-3-phosphate dehydrogenase gene (GAPDH), Ubiquitin gene (UBQ), eukaryotic elongation factor 1-αgene (eEF-1α), α-tubulin gene (α-TUB), ß-tubulin gene (ß-TUB), eukaryotic translation initiation factor 4α-1 gene (eIF-4α) and NAC domain protein gene(NAC) in a series of 30 M. lutarioriparia samples followed by statistical algorithms geNorm and Normfinder to analyze the gene expression stability. The results indicated that eIF-4αand UBQ were the most stable expressed genes while CBP20 showed as the least stable among all the samples. Based on above research, we recommend that at least two top-ranked reference genes should be employed for expression data normalization. The best genes selected in this study will provide a starting point to select reference genes in the future in other tissues and under other experimental conditions in this energy crop candidate.

Selenium-Substituted Diketopyrrolopyrrole Polymer for High-Performance p-Type Organic Thermoelectric Materials.

Development of high-performance organic thermoelectric (TE) materials is of vital importance for flexible power generation and solid-cooling applications. Demonstrated here is the significant enhancement in TE performance of selenium-substituted diketopyrrolopyrrole (DPP) derivatives. Along with strong intermolecular interactions and high Hall mobilities of 1.0-2.3 cm2 V-1 s-1 in doping-states for polymers, PDPPSe-12 exhibits a maximum power factor and ZT of up to 364 µW m-1 K-2 and 0.25, respectively. The performance is more than twice that of the sulfur-based DPP derivative and represents the highest value for p-type organic thermoelectric materials based on high-mobility polymers. These results reveal that selenium substitution can serve as a powerful strategy towards rationally designed thermoelectric polymers with state-of-the-art performances.

Critical Role of Surface Energy in Guiding Crystallization of Solution-Coated Conjugated Polymer Thin Films.

It is well-known that substrate surface properties have a profound impact on the morphology of thin films solution coated atop and the resulting solid-state properties. However, design rules for guiding the substrate selection have not yet been established. Such design rules are particularly important for solution-coated semiconducting polymers, as the substrate-directed thin film morphology can impact charge transport properties by orders of magnitude. We hypothesize that substrate surface energies dictate the thin film morphology by modulating the free energy barrier to heterogeneous nucleation. To test this hypothesis, we systematically vary the substrate surface energy via surface functionalization techniques. We perform in-depth morphology and device characterizations to establish the relationship between substrate surface energy, thin film morphology and charge transport properties, employing donor-acceptor (D-A) conjugated polymers. We find that decreasing the substrate surface energy progressively increases thin film crystallinity, degree of molecular ordering, and extent of domain alignment. Notably, the enhanced morphology on the lowest surface energy substrate leads to a 10-fold increase in the charge carrier mobility. We further develop a free energy model relating the substrate surface energy to the penalty of heterogeneous nucleation from solution in the thin film geometry. The model correctly predicts the experimental trend, thereby validating our hypothesis. This work is a significant step toward establishing design rules and understanding the critical role of substrates in determining morphology of solution-coated thin films.

Multiscale assembly of solution-processed organic electronics: the critical roles of confinement, fluid flow, and interfaces.

Organic semiconducting small molecules and polymers provide a rich phase space for investigating the fundamentals of molecular and hierarchical assembly. Stemming from weak intermolecular interactions, their assembly sensitively depends on processing conditions, which in turn drastically modulate their electronic properties. Much work has gone into molecular design strategies that maximize intermolecular interactions and encourage close packing. Less understood, however, is the non-equilibrium assembly that occurs during the fabrication process (especially solution coating and printing) which is critical to determining thin film morphology across length scales. This encompasses polymorphism and molecular packing at molecular scale, assembly of π-bonding aggregates at the tens of nanometers scale, and the formation of domains at the micron-millimeter device scale. Here, we discuss three phenomena ubiquitous in solution processing of organic electronic thin films: the confinement effect, fluid flows, and interfacial assembly and the role they play in directing assembly. This review focuses on the mechanistic understanding of how assembly outcomes couple closely to the solution processing environment, supported by salient examples from the recent literature.