Facet-Selective Growth of Organic Heterostructured Architectures via Sequential Crystallization of Structurally Complementary π-Conjugated Molecules

Lateral epitaxial growth of two-dimensional organic heterostructures

Two-dimensional organic lateral heterostructures (2D OLHs) are attractive for the fabrication of functional materials. However, it is difficult to control the nucleation, growth and orientation of two distinct components. Here we report the combination of two methods-liquid-phase growth and vapour-phase growth-to synthesize 2D OLHs from perylene and a perylenecarboxaldehyde derivative, with a lateral size of ~20 μm and a tunable thickness ranging from 20 to 400 nm. The screw dislocation growth behaviour of the 2D crystals shows the spiral arrangement of atoms within the crystal lattice, which avoids volume expansion and contraction of OLH, thereby minimizing lateral connection defects. Selective control of the nucleation and sequential growth of 2D crystals leads to structural inversion of the 2D OLHs by the vapour-phase growth method. The resulting OLHs show good light-transport capabilities and tunable spatial exciton conversion, useful for photonic applications. This synthetic strategy can be extended to other families of organic polycyclic aromatic hydrocarbons, as demonstrated with other pyrene and perylene derivatives.

Morphology-Dependent Optoelectronic Properties of Pentacene Nanoribbon and Nanosheet Crystallite

Organic, single crystals have emerged as unique optoelectrical materials due to their highly ordered structure and low defects. In this work, pentacene nanoribbons and nanosheets were selectively fabricated by controlling their growth temperature. The results show that their photoluminescence (PL) activity and electrical properties were strongly dependent on their geometrical morphology and molecular stacking mode such as the degree of π-orbital overlap and intermolecular interaction. The pentacene nanoribbon crystal exhibited a higher PL intensity compared with the nanosheet configuration; conversely, its electrical conductivity was poor. The low-temperature PL measurement indicated that there are stronger π-π stacking interactions in the nanosheet crystal than in the nanoribbon crystal, leading to exciton quenching and higher conductivity. Our study demonstrated that a unique optoelectronic property of organic crystals can be obtained by controlling the crystal's morphology, which offers potential guidance for the future design and development of organic crystal optoelectronics.

Molecular doping of nucleic acids into light emitting crystals driven by multisite-intermolecular interaction

We reveal the fundamental understanding of molecular doping of DNAs into organic semiconducting tris (8-hydroxyquinoline) aluminum (Alq₃) crystals by varying types and numbers of purines and pyrimidines constituting DNA. Electrostatic, hydrogen bonding, and π-π stacking interactions between Alq₃ and DNAs are the major factors affecting the molecular doping. Longer DNAs induce a higher degree of doping due to electrostatic interactions between phosphate backbone and Alq₃. Among four bases, single thymine bases induce the multisite interactions of π-π stacking and hydrogen bonding with single Alq₃, occurring within a probability of 4.37%. In contrast, single adenine bases form multisite interactions, within lower probability (1.93%), with two-neighboring Alq₃. These multisite interactions facilitate the molecular doping into Alq₃ particles compared to cytosines or guanines only forming π-π stacking. Thus, photoluminescence and optical waveguide phenomena of crystals were successfully tailored. This discovery should deepen our fundamental understanding of incorporating DNAs into organic semiconducting crystals.

Vapor-Phase Living Assembly of π-Conjugated Organic Semiconductors

In contrast to well-studied amphiphilic block copolymers (BCPs) and π-stacked dyes, living assembly of hydrophobic π-conjugated materials has not yet been explored to date. Using a microspacing physical vapor transport (PVT) technique, the prefabricated microrods of organic semiconductors involving 9,10-dicyanoanthracene (DCA, A) or its binary alloy (B) can act as seeds to initiate living homoepitaxial growth from their ends, giving elongated microrods with controlled length. Red-green-red tricolor fluorescent microrod heterostructures with low dispersity are further realized by living heteroepitaxial growth of B microrod blocks on A seed microrod tips. Upon varying the growth sequence of each block, reverse triblock microrods are also accessible. Such a seed-induced living growth is applicable to triblock microrod heterostructures of more binary combinations as well as even more complex penta- and hepta-block heterostructures comprising A and B. By virtue of a convenient vapor-phase growth method, the present work demonstrates the generality of living assembly of π-conjugated materials.

Organic multicomponent microparticle libraries

Multimetallic nanostructures can be synthesized by integrating up to seven or eight metallic elements into a single nanoparticle, which represent a great advance in developing complex multicomponent nanoparticle libraries. Contrary, organic micro- and nanoparticles beyond three π-conjugated components have not been explored because of the diversity and structural complexity of molecular assemblies. Here, we report a library of microparticles composed of an arbitrary combination of four luminescent organic semiconductors. We demonstrate that the composition and emission color of each domain as well as its spatial distribution can be rationally modulated. Unary, binary, ternary, and quaternary microparticles are thus realized in a predictable manner based on the miscibility of the components, resulting in mixed-composition phases or alloyed or phase separated heterostructures. This work reports a simple yet available synthetic methodology for rational modulation of organic multicomponent microparticles with complex architectures, which can be used to direct the design of functional microparticles.

The synthesis of alloyed complex multicomponent micro- and nanoparticles composed of organic molecules is challenging. Here, the authors demonstrate a library of mixed composition organic microparticles in comprising up to four compounds in their structure.

Color- and Dimension-Tunable Light-Harvesting Organic Charge-Transfer Alloys for Controllable Photon-Transport Photonics

An electron donor/acceptor pair comprising perylene (Pe) and 9,10-dicyanoanthracene (DCA) was specifically designed to construct organic charge-transfer (CT) alloys via weak CT interaction through a solution co-assembly route. By adjusting the molar ratio between Pe and DCA, we achieve color- and dimension-tunable CT alloy assemblies involving one-dimensional (1D) (DCA)_1-x (Pe)_x (0 ≤ x ≤10 %) microribbons and two-dimensional (2D) (Pe)_1-y (DCA)_y (0 ≤ y ≤5 %) nanosheets as a consequence of energy transfer from DCA or α-Pe to Pe-DCA CT complex. Importantly, dimension-related optical waveguiding performances are also revealed: continuously adjustable optical loss in 1D (DCA)_1-x (Pe)_x microribbons and successive conversion from isotropic waveguide to anisotropic waveguide in 2D (Pe)_1-y (DCA)_y nanosheets. The present work provides a desired platform for in-depth investigation of light-harvesting organic CT alloy assemblies, which show promising applications in miniaturized optoelectronic devices.

A combination of an organic alloy and a heterojunction towards a rod-tail helix architecture with dual-color-emitting properties

An organic alloy can be regarded as a homogeneous solid solution wherein an isostructural molecule is randomly distributed in a host molecule, compared to an organic heterojunction where dissimilar materials generate an interface between two layers or regions. Herein, we fabricate an unprecedented novel BA@BA_0.72BN_0.28 heterostructure with a rod-tail helix configuration, in which the helical dual-component BA_0.72BN_0.28 alloy can be grown in a controllable manner onto the mono-component BA microrod, forming an organic core-shell micro-structure. In particular, the process of co-assembly formed could be described as the combined construction of an organic alloy and a heterojunction, and the co-assembly possesses the distinctive property of dual-color luminescence. This complex heterostructured architecture is achieved through a stepwise seed-induced growth method and the present solution-phase route allows us to construct more sophisticated organic luminescent heterostructured materials.

Reactivity triggered by an organic microcrystal interface: a case study involving an environmentally benign, aromatic boric acid reaction

At a self-assembled {002} crystal-solution interface, inactive 9-anthracene boric acid was transformed into a highly active state, for catalyst-free aromatic substitution and oxidation.

Vapour-Phase Epitaxial Growth of Dual-Colour-Emitting DCM-Perylene Micro-Heterostructure Optical Waveguides

Organic micro-heterostructures (MHS) with dual optical emissions are essential to produce miniaturized optical waveguides for wavelength division multiplexing technologies. The bimolecular MHS produced by solution-based bottom-up self-assembly technique often leads to poor surface smoothness, edge imperfection, defects, and unwanted thin films deposits. Conversely, sequential sublimation technique at ambient pressure facilitates effective integration of α-perylene micro-square with dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl) 4H-pyran (DCM) microrods in an epitaxial manner to produce MHS. The obtained DCM/perylene MHS act as optical waveguides to produce red (λ_max ≈670 nm) or/and yellow (λ_max ≈607 nm) dual optical outputs via an energy transfer mechanism depending upon the heterostructures geometry and optical excitation positions. The presented dual-color emitting MHS optical waveguides are essential for the integrated nano-photonic and optoelectronic device structures.

Hierarchical self-assembly of organic heterostructure nanowires

Organic heterostructures (OHSs) integrating the intrinsic heterostructure characters as well as the organic semiconductor properties have attracted intensive attention in material chemistry. However, the precise bottom-up synthesis of OHSs is still challenging owing to the general occurrence of homogeneous-nucleation and the difficult manipulation of noncovalent interactions. Herein, we present the rational synthesis of the longitudinally/horizontally-epitaxial growth of one-dimensional OHSs including triblock and core/shell nanowires with quantitatively-manipulated microstructure via a hierarchical self-assembly method by regulating the noncovalent interactions: hydrogen bond (−15.66 kcal mol⁻¹) > halogen bond (−4.90 kcal mol⁻¹) > π-π interaction (−0.09 kcal mol⁻¹). In the facet-selective epitaxial growth strategy, the lattice-matching and the surface-interface energy balance respectively facilitate the realization of triblock and core/shell heterostructures. This hierarchical self-assembly approach opens up avenues to the fine synthesis of OHSs. We foresee application possibilities in integrated optoelectronics, such as the nanoscale multiple input/out optical logic gate with high-fidelity signal.

Organic heterostructures attract attention in material chemistry but the precise bottom-up synthesis is still challenging. Herein the authors present a hierarchical self-assembly approach to synthesize one-dimensional organic heterostructures by regulating the noncovalent interactions.

Epitaxial growth of dual-color-emitting organic heterostructures via binary solvent synergism driven sequential crystallization

The controlled construction of organic heterostructured architectures derived from molecules with similar nucleation thresholds and concentrations has been rare and remains a great challenge. Herein, we report a sequential epitaxial growth to synthesize dual-color-emitting organic heterostructures with 9,10-bis(phenylethynyl)anthracene (BPEA) microwire trunks and tris-(8-hydroxyquinoline)aluminium (Alq3) microstructure branches by an anti-solvent induced sequential crystallization strategy. During the epitaxial growth process, the hydrogen-bonding interactions of the anti-solvent and solvent cause a large change in the solubility and crystallization rate of BPEA and Alq3 molecules in the mixed system, which facilitates sequential crystallization of organic molecule pairs with similar nucleation thresholds and concentrations into desired heterostructures by manipulating the synergism of anti-solvents and solvents. The Förster resonant energy transfer process in heterostructures could be modulated by varying the structure of heterostructures, such as the shape, amount and angles of the branches. The present synthesis strategy provides a unique insight into the detailed formation mechanism of complex organic heterostructures, further guiding the construction of more functional heterostructure materials.

In Situ Construction of One-Dimensional Component-Interchange Organic Core/Shell Microrods for Multicolor Continuous-Variable Optical Waveguide

The core/shell micro-/nanostructures with versatility, tunability, stability, dispersibility, and biocompatibility are widely applied in optics, biomedicine, catalysis, and energy. Organic micro-/nanocrystals have significant applications in miniaturized optoelectronics because of their controllable self-assembly behavior, tunable optical properties, and tailor-made molecular structure. Nevertheless, the advanced organic core/shell micro-/nanostructures, which possess multifunctionality, flexibility, and higher compatibility, are rarely demonstrated because of the dynamic nature of molecular self-assembly and the complex epitaxial relationship of material combination. Herein, we demonstrate the one-dimensional organic core/shell micro-/nanostructures with component interchange, which originates from the 4,4'-((1 E,1' E)-(2,5-dimethoxy-1,4-phenylene)bis(ethene-2,1-diyl))dipyridine (DPEpe) single-crystal microrods or the DPEpe-HCl single-crystal microrods after a reversible protonation or deprotonation process. Notably, the DPEpe/DPEpe-HCl core/shell microrods display vivid visualizations of tunable emission color via an efficient energy-transfer process during the stepwise formation of a shell layer. More significantly, these DPEpe/DPEpe-HCl and DPEpe-HCl/DPEpe core/shell microrods cooperatively demonstrate the multicolor optical waveguide properties continuously adjusted from green [CIE (0.326, 0.570)], to yellow [CIE (0.516, 0.465)], and to red [CIE (0.614, 0.374)]. Our investigation provides a new strategy to fabricate the organic core/shell micro-/nanostructures, which can eventually contribute to the advanced organic optoelectronics at the micro-/nanoscale.