A General Synthetic Approach of Organic Lateral Heterostructures for Optical Signal Converters in All-Color Wavelength

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE18 Mar 2022A General Synthetic Approach of Organic Lateral Heterostructures for Optical Signal Converters in All-Color Wavelength Qiang Lv, Xue-Dong Wang, Wan-Ying Yang, Kai-Li Wang, Chao-Fei Xu, Min Zheng and Liang-Sheng Liao Qiang Lv National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Research Center of Cooperative Innovation for Functional Organic/Polymer Material Micro/Nanofabrication, Soochow University, Suzhou, Jiangsu 215123 Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 Google Scholar More articles by this author , Xue-Dong Wang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 Google Scholar More articles by this author , Wan-Ying Yang Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 Google Scholar More articles by this author , Kai-Li Wang Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 Google Scholar More articles by this author , Chao-Fei Xu Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 Google Scholar More articles by this author , Min Zheng *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] National Engineering Laboratory for Modern Silk, College of Textile and Clothing Engineering, Research Center of Cooperative Innovation for Functional Organic/Polymer Material Micro/Nanofabrication, Soochow University, Suzhou, Jiangsu 215123 Jiangsu General Science & Technology Co., Ltd., Suzhou Industrial Park, Suzhou, Jiangsu 215123 Google Scholar More articles by this author and Liang-Sheng Liao *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou, Jiangsu 215123 Macao Institute of Materials Science and Engineering, Macau University of Science and Technology, Taipa 999078, Macau SAR Google Scholar More articles by this author https://doi.org/10.31635/ccschem.022.202101640 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Organic heterostructures with precisely defined compositions, architectures, and interfaces are considered promising building blocks for integrated optoelectronic devices. However, it remains a great challenge to rationally design and synthesize a heterostructure with tunable performance for promising applications such as optoelectronic devices. Herein, we report a universal strategy for the synthesis of organic lateral heterostructures (OLHs) with tunable function and optical properties. We fabricated cocrystals based on the tunable intermolecular distance (dπ–π from 3.33 to 3.48 Å) of Benzo[ghi]perylene (BGP)-based driven by arene-perfluoroarene interaction or charge transfer interaction; these different components were selectively constructed into organic solid solution microwires or OLHs. Importantly, the solid solution microwires obtained could be epitaxially grown on the BGP-tetrabromophthalicanhydride trunk microwire to construct a series of OLHs microwires, which led to the successful demonstration of both photonic signal conversion and optical logic gate in all-color wavelength. This work gives a new insight into the fine synthesis of heterostructures with tunable structures/performances, providing predictable synthetic pathways to multifunctional organic heterostructures for the future realization of integrated optoelectronics. Download figure Download PowerPoint Introduction Complex heterostructured micro/nanomaterials with multi-functionalities1 and novel performances2 are essential for many applications, including catalysis,3 plasmonic,4 electronics,5 optoelectronic,6 and so on.7 Among them, one-dimensional (1D) branch heterostructures composed of two or more distinct materials, possessing different space distribution (vertical or lateral) and high-density branches grown on a trunk, are particularly attractive micro/nanomaterials for a variety of applications.8–11 In the last two decades, the controlled synthesis of inorganic branch heterostructures nanomaterials has been intensively investigated through the vapor–liquid–solid (VLS) method8 or chemical vapor deposition (CVD) method10 and others.12 A typical example is the case of eight CdS nanocrystals hierarchically grown into the central region of CdSe nanorods to form octapod-shaped nanocrystals via cation exchange and seeded growth method.13 However, compared with inorganic materials, organic semiconductors exhibit obvious advantages for optoelectronics’ applications14,15 due to their two-photon absorption cross sections 16 and broad spectral tunability17 as well as designable molecular structures.18–20 Specifically, the organic crystals are composed of one or more different organic molecules that inherit single-crystal intrinsic features of long-range order and free defects21; also, they provide a platform for the rational design and flexible construction of heterostructures based on the diverse library of organic materials and various intermolecular interactions.22–24 Until now, lots of efforts have been devoted to preparing organic branch heterostructures that exhibit attractive optoelectronic properties.25,26 For example, based on the organic crystal, the synthesis of 1D branched heterostructures with multiple nanowire branches has been demonstrated with application in photonic devices such as signal conversion and multi-channel optical waveguides.11 Moreover, a series of branched heterostructures with different morphologies have been reported, including microplates, spindles, and ribbon-like structures that epitaxially grow on the microwire backbone.27–29 However, for the same kind of 1D branch heterostructures with rigorous morphology, modulating their optical properties to fulfill the requirement of integrated optical circuits such as signal converters and logic gates are rarely reported.30 Typically, organic crystals with different optical properties have distinct crystal structures, making it difficult to control the facet selective epitaxial growth mode of the secondary components to maintain the same structure of the heterostructure while changing the chemical/physical properties.27 Although many efforts have been devoted to preparing various typical organic heterostructures (core-shell, triblock, and so on) by integrating distinct organic counterparts, their molecular structures must be changed significantly to tune the emission wavelength, which limits their flexible applications in optoelectronics.31 In this work, we report a generalizable mix-and-match synthetic strategy of organic heterostructures with tunable structure and optical properties that combines organic solid solutions32 and heterostructures (Figure 1a). We prepared a series of Benzo[ghi]perylene (BGP)-based cocrystals, including BGP-octafluoronaphthalene (OFN), BGP-tetrafluorotere-phthalonitrile (TFP), BGP-tetrafluorophthalicanhydride (TFPA), BGP-1,2,4,5-benzenetetranitrile (TCNB), BGP-tetrabromophthalicanhydride (TBPA) through the solution self-assembly method. At the same time, the formation of these selected cocrystals was driven by arene-perfluoroarene (AP)33 or charge transfer (CT)23 interaction. Based on the tunable intermolecular distances (dπ–π from 3.33 to 3.48 Å) and competitive intermolecular interactions34 of the cocrystals, the components could be constructed selectively into organic solid solution microwires or organic lateral heterostructures (OLHs). Importantly, the solid solution microwires obtained could match the BGP-TBPA trunk microwire to realize a series of OLHs microwires with color-tunable emission. Moreover, the structures of OLHs could be further adjusted by tuning the stoichiometric ratio of multi-components. Thus, a series of optical signal converts and multi-channel optical routers were realized successfully based on the OLHs with all-color-tunable photoluminescent. Our present work provides a desired platform for in-depth investigation of organic heterostructures with novel and enhanced performance, opening a new window for flexible designing and building complex multifunctional optoelectronic modules. Figure 1 | (a) Scheme for designing 1D branch heterostructures with color-tunable emission performance. (b) The molecular structures of the BGP-OFN cocrystal and BGP-TFP, BGP-TFPA, and BGP-TCNB cocrystal. Color scheme: C, grey; H, white; F, cyan; CN, blue; O, red. The corresponding intermolecular distances. (c) Calculated energy level diagrams of the BGP-OFN, BGP-TFP, BGP-TFPA, and BGP-TCNB cocrystals. (d) Representation for the energy-transfer process from the BGP-OFN cocrystal to BGP-TFP/TFPA/TCNB cocrystal. Download figure Download PowerPoint Experimental Methods Chemicals BGP (CAS: 191-24-2), OFN (CAS: 313-72-4), TFP (CAS: 1835-49-0), TCNB (CAS: 712-74-3), TFPA (CAS: 652-12-0), TBPA (CAS: 632-79-1) were purchased from Sigma-Aldrich Co. (St. Louis, MO, United States). The dichloromethane (CH2Cl2, A.R.), methanol (A.R.) and ethanol (A.R.), cyclohexane (A.R.), and n-hexane (A.R.) solvents were purchased from Beijing Chemical Ltd. (Beijing, China). In addition, all compounds and solvents were used without further treatment. Methods (1) Self-assembly of organic cocrystals (BGP-OFN, BGP-TFP, and BGP-TCNB): Typically, 10 mL of the monomer solutions containing 0.1 mmol BGP and 0.1 mmol OFN (TFP or TCNB) in dichloromethane (DCM) were injected quickly into 20 mL of ethanol. Then the mixed solution was directly drooped onto the quartz substrate. With the solvent evaporation, the mixtures would reach supersaturation, and the BGP-OFN (BGP-TFP and BGP-TCNB) cocrystals were observed. (2) Self-assembly of organic cocrystals (BGP-TFPA and BGP-TBPA): Typically, 10 mL of the monomer solutions containing 0.1 mmol BGP and 0.1 mmol TFPA (TBPA) in DCM were injected quickly into 20 mL of an n-hexane. Then the mixed solution was directly drooped onto the quartz substrate. With the solvent evaporation, the mixtures would reach supersaturation, and the BGP-TFPA (BGP-TBPA) cocrystals were observed. (3) Co-assembly of BGP-OFN-TFP, BGP-OFN-TFPA, and BGP-OFN-TCNB organic solid solution microwires: Typically, 10 mL of the monomer solutions containing BGP, OFN, and TFP in DCM with extent molar ratio (NBGP: NOFN: NTFP = 1:1:0.1, CBGP = 5 mM) were injected quickly into 20 mL of a mixed solvent (ethanol and n-hexane, Vethanol: Vn-hexane = 15:5). Next, the mixed solvent was directly dropped onto a quartz plate, with subsequent evaporation of the mixed solvent. The mixtures reached supersaturation rapidly and underwent crystal growth. Likewise, BGP-OFN-TFPA and BGP-OFN-TCNB were also obtained by the above method. (4) Synthesis of [email protected] lateral heterostructures: Typically, 10 mL of the monomer solutions containing BGP, OFN, and TBPA in DCM with extent molar ratio (NBGP : NOFN:NTBPA = 2:1:1, CBGP = 2 mM) were quickly injected into 20 mL of a mixed solvent (ethanol and n-hexane, Vethanol:Vn-hexane = 15:5). Then the mixed solvent was dropped directly onto a quartz plate, with subsequent evaporation of the mixed solvent. The mixtures reached supersaturation rapidly and underwent crystal growth. (5) Synthesis of [email protected], [email protected], and [email protected] lateral heterostructures: In a typical experiment, 10 mL of the monomer solutions containing BGP, OFN, TBPA, TFP in DCM with extent molar ratio (NBGP:NOFN:NTBPA:NTFP = 2:1:1:0.1, CBGP = 2 mM) were injected quickly into 20 mL of a mixed solvent (ethanol and n-hexane, Vethanol:Vn-hexane = 15:5). Then the mixed solvent was dropped directly onto the quartz plate, with subsequent evaporation of the mixed solvent. The mixtures reached supersaturation rapidly and underwent crystal growth. Then the dispersed solution was dropped onto a quartz substrate, and the solvent was completely evaporated at room temperature to obtain heterostructures. Likewise, [email protected] and [email protected] were also obtained by the above method. Results and Discussion We prepared a series of BGP-based cocrystals through a facile solution self-assembly method, including the BGP-OFN cocrystal driven by AP interaction, and the BGP-TFP, BGP-TFPA, and BGP-TCNB cocrystals driven by CT interaction ( Supporting Information Figure S1). Among them, the interaction strength of CT was greater than AP ( Supporting Information Table S1). The fluorescence microscopy (FM) images of these CT cocrystals demonstrated that they were prepared successfully ( Supporting Information Figure S2). As shown in Figure 1b, the intermolecular distances (dπ–π) between the adjacent components of BGP-OFN (3.37 Å), BGP-TFP (3.33 Å), BGP-TFPA (3.35 Å), and BGP-TCNB (3.37 Å) were highly similar, evident by Materials Studio calculation, indicating that a certain amount of these donor components of CT cocrystals were readily incorporated into the BGP-OFN systems. In order to obtain the detailed structural information of these BGP-based cocrystals, we carefully studied their molecular packing modes. As shown in Supporting Information Figures S3–S6, the BGP-based cocrystals displayed a similar molecular packing mode; two molecules of BGP-OFN, BGP-TFP, BGP-TFPA, and BGP-TCNB cocrystals were nearly planar and stacked on each other alternately. Furthermore, density functional theory (DFT) calculations were performed on the BGP-based cocrystals to better understand their optical properties. The energy-level diagram of the materials (Figure 1c) showed that the BGP-OFN cocrystal had a higher energy gap (ca. 3.07 eV) compared with BGP-TFP (ca. 2.26 eV), BGP-TFPA (ca. 2.01 eV), and BGP-TCNB (ca. 1.99 eV) cocrystals, which might have allowed the occurrence of an energy transfer process from the BGP-OFN to CT cocrystals.31 In addition, we found that the highest occupied molecular orbital (HOMO) of these cocrystals was almost localized on the BGP molecule, whereas the lowest unoccupied molecular orbital (LUMO) were respectively distributed on the OFN, TFP, TFPA, and TCNB molecules ( Supporting Information Figures S10 and S11) attributed to the donor–acceptor cocrystal system. The photoluminescence (PL) and absorption spectra of these BGP-based cocrystals further demonstrated the possibility of an energy transfer process. Supporting Information Figure S9 showed that the PL spectrum of BGP-OFN displayed a good overlap with the absorption spectra of the BGP-TFP, BGP-TFPA, and BGP-TCNB. Moreover, the pure BGP-OFN microwires had a fluorescence lifetime of ca. 15.2 ns, which reduced to 13.5, 10.3, and 10.1 ns of BGP-OFN-TFP, BGP-OFN-TFPA, and BGP-OFN-TCNB solid solutions, respectively. Thus, an energy-transfer process from BGP-OFN cocrystal to BGP-based CT cocrystals could occur ( Supporting Information Figures S12 and S13). In addition, the AP interaction of BGP-OFN cocrystal was kind of a weaker electrostatic interaction compared with the CT interaction of BGP-TFP, BGP-TFPA, and BGP-TCNB cocrystals reported previously. The PL spectrum of BGP-OFN presented two emission peaks at ca. 473 and 500 nm due to the AP interaction, while these CT cocrystals all displayed a single band emission peak. In general, (1) the BGP-based cocrystals had well-matched crystal structures, including similar molecular packing mode and the distance of adjacent molecules, necessary for constructing a solid solution. (2) a good overlap of the emission spectrum of BGP-OFN and the absorption spectrum of CT cocrystals existed, indispensable for efficient energy transfer. (3) the systems included two types of intermolecular interactions, namely AP and CT interactions, which might have been facilitated by the CT acceptor molecules doped into the BGP-OFN crystals. Based on the above analysis, a possible energy-transfer mechanism in the solid solution composed of AP and CT cocrystal was proposed, as displayed in Figure 1d: We expect that if the BGP-OFN donor is excited by 375 nm light, its excitation energy will transfer to a nearby BGP-TFP or BGP-TFPA, BGP-TCNB acceptors, and finally emits the corresponding light of the acceptors. Therefore, we can achieve a solid solution with color-tunable emission based on the different acceptors. As a proof of concept, the BGP-OFN cocrystal was selected as the host material, and the three types of CT cocrystals as the guest materials (BGP-TFP, BGP-TFPA, BGP-TCNB) to construct a solid solution with tunable optical properties. In a typical synthesis, we used a one-pot solution self-assembly method to prepare a BGP-OFN-TFP solid solution. First, the mixed stock solution containing both BGP (CBGP = 5 mM) and OFN (COFN = 5 mM), TFP (CTFP = 0.5 mM) in DCM was preprepared (the molar ratio between BGP, OFN, and TFP, NBGP:NOFN:NTFP = 1:1:0.1). Second, the preprepared solution was added to n-hexane solution (VDCM:Vn-hexane = 1:2). The mixture was then dropped onto the quartz substrate. Finally, the formation of BGP-OFN-TFP microwires was obtained after the solvents were completely evaporated. Likewise, we prepared the BGP-OFN-TFPA and BGP-OFN-TCNB microwires through a one-pot solution self-assembly method. As shown in Figures 2a–2d, the FM images of these organic solid solutions with different light emissions demonstrated successful preparation. Apparently, the BGP-OFN microwires obtained emitted blue light (Figure 2a), the BGP-OFN-TFP microwires emitted green light (Figure 2b), the BGP-OFN-TFPA microwires emitted yellow light (Figure 2c), and the BGP-OFN-TCNB microwires emitted red light (Figure 2d), realizing uniform and tunable emission colors in a wide color gamut from blue to red. The corresponding PL spectra of these microwires (Figure 2e) showed that the BGP-OFN microwires presented two emission peaks at ∼ 473 and 500 nm, whereas the BGP-OFN-TFP displayed a single PL band at 522 nm, the BGP-OFN-TFPA showed a single PL band at 558 nm, and the BGP-OFN-TCNB presents a single PL band at 606 nm. Regarding the single peak of PL obtained from the solid solution, compared with BGP-OFN cocrystal, we speculated that the high-efficiency energy transfer occurred from BGP-OFN cocrystal to these CT cocrystals. Correspondingly, the Commission Internationale de l’Eclairage (CIE) color coordinate values of these complex microwires were calculated using their emission spectra (Figure 2f), which further confirmed the successful modulation of organic microcrystals’ light emission by constructing organic solid solutions with different guest materials (BGP-TFP, BGP-TFPA, BGP-TCNB). Moreover, we deduced that the acceptor molecules were completely and uniformly added into the BGP-OFN host in the preparation ratio. As a proof of concept, we conducted a series of micro-area PL spectra measurements of multiple organic solid solution microwires to verify our claim. As shown in Supporting Information Figure S14, the emission spectra of multiple solid solution microwires were also almost identical, which further proved the emission uniformity of solid solution obtained by this method. We then conducted the transient absorption spectroscopy measurements to obtain the detailed optical properties of organic solid solutions and confirm their composition ( Supporting Information Figure S9). Interestingly, we found that the absorption spectra of the solid solution both included the absorption peaks of BGP-OFN host and the corresponding guest materials (BGP-TFP, BGP-TFPA, BGP-TCNB), confirming that the organic solid solutions obtained composed BGP-OFN host, BGP-TFP, and other guest materials, as well as the AP and CT intermolecular interaction existence in the systems. Notably, the BGP-OFN cocrystals as typical AP assemblies not only showed high solid photoluminescence quantum yields (PLQYs) of 85% in solid ( Supporting Information Table S2) but also significantly improved the PLQYs of as-prepared organic solid solutions. As shown in Supporting Information Table S2, the obtained BGP-OFN-TFP, BGP-OFN-TFPA, and BGP-OFN-TCNB organic solid solutions presented much higher PLQYs than that of the BGP-TFP, BGP-TFPA, and BGP-TCNB cocrystals; their PLQYs could be improved by 208%, 209%, and 249%, respectively, making them promising building blocks with highly emissive solid materials for the construction of advanced optical devices. To further confirm the crystal structures, X-ray diffraction (XRD) curves of these microwires were collected. As shown in Figure 2g, no XRD characteristics of the BGP-TFP, BGP-TFPA, and BGP-TCNB acceptors were identified in the XRD curves of the corresponding organic solid solutions; meanwhile, they keep the same crystal structure of BGP-OFN cocrystal, indicating that the organic acceptor molecules incorporated into the host materials without affecting its inherent crystal structure. Moreover, the average sizes of BGP-OFN cocrystals and solid solutions were ∼ 65 and 75 μm, respectively. Furthermore, the average size of CT cocrystals was ∼ 55 μm ( Supporting Information Figures S15–S18). Figure 2 | (a–d) FM images of BGP-OFN, BGP-OFN-TFP, BGP-OFN-TFPA, and BGP-OFN-TCNB solid solutions, respectively. All scale bars are 20 μm. (e) The PL spectra of BGP-OFN, BGP-OFN-TFP, BGP-OFN-TFPA, and BGP-OFN-TCNB microwires, (f) The corresponding CIE coordinate values of these microwires with different emission colors. (g) The XRD patterns of BGP-OFN, BGP-OFN-TFP, BGP-OFN-TFPA, and BGP-OFN-TCNB microwires. Download figure Download PowerPoint As shown in Figure 3a, when we continued to select the appropriate CT cocrystal as the guest materials (BGP-TBPA) to construct the solid solution, we found that using the BGP-TBPA cocrystal as the guest material failed to add to the BGP-OFN cocrystal to form a solid solution, and instead generated OLHs during the co-assembly process of BGP, OFN, and TBPA molecules ( Supporting Information Tables S3–S5). Under this condition, we deduced that the larger dπ–π of BGP-TBPA (3.48 Å) cocrystal than BGP-OFN (3.37 Å) might have resulted in the failure of TBPA molecules to add to the BGP-OFN cocrystal ( Supporting Information Figures S7 and S8). On the other hand, the BGP-TBPA cocrystal had strong CT intermolecular interaction, facilitating them to nucleate initially and then grow into microwires in the mixed solution. These prepared BGP-TBPA cocrystals were capable of serving as a substrate for the epitaxial growth of BGP-OFN cocrystal on the lateral sides. In addition, the number of BGP-OFN branches from one to two could be finely tuned by carefully adjusting the stoichiometric ratio of BGP-OFN and BGP-TFPA cocrystal (NBGP-TFPA/NBGP-OFN). To deeply understand the epitaxial growth process of the OLHs, we recorded the video data by tracking the real-time growth processes. As shown in Figures 3b1–3b4, the bright-field images of branch microwires were captured, defined as the formation time of BGP-OFN as 0 s. At the early stage, the BGP-TBPA trunk nucleated from the mixed solution and then elongated to tens of micrometers. After a period, the BGP-OFN branch started to nucleate on the lateral side of the BGP-TBPA microwire and then grew along the horizontal axis of the trunk. Notably, the short branch microwire was formed first, sticking out of one side of the trunk microwire, attributed to the higher surface energy of one tip side relative to the other tip side (Figure 3b2). Finally, as the reaction time increased, the BGP-OFN branch microwires grew along on the BGP-TBPA trunk microwire with their two tips distributed evenly on both sides of the trunk, instead of just appearing on one side (Figures 3b3 and 3b4). Figure 3c displays an FM image of an individual single-lateral microwire; the trunk microwire exhibits orange light corresponding to the BGP-TBPA, whereas the branch microwire presents blue light corresponding to the BGP-OFN when excited with unfocused UV light. In addition, the FM image of an individual double-lateral microwire (Figure 3d) showed that the branch microwires on both sides were parallel to each other. The spatially resolved spectra of branch microwire were collected in three different positions, namely the junction region, the backbone, and the branch (marked as 1, 2, 3 in the FM image of Supporting Information Figure S15a2, respectively). It could be seen that the PL of the backbone corresponded to the PL of individual BGP-TBPA, and the PL of the branch corresponding to the PL of BGP-OFN, while the PL of the junction included the PL of individual BGP-TBPA and BGP-OFN. These results confirmed that the branch heterostructures were composed of the BGP-TBPA trunk and BGP-OFN branch. Figure 3 | (a) Representation of the epitaxial growth of the [email protected] OLHs. (b1–b4) The evolution processes of [email protected] OLHs at different time intervals (b1, 0 s; b2, 7 s; b3, 12 s; b4, 23 s) were recorded by the corresponding real-time video. All Scale bars are 20 μm. (c) FM image of a typical single-lateral microwire. The scale bar is 20 μm. (d) FM image of a typical double-lateral microwire. The scale bar is 20 μm. (e) SEM image of a typical OLHs. (f) The predicted growth morphologies of BGP-OFN and BGP-TBPA cocrystal obtained by Material Studio simulation, and the lattice mismatching rate of BGP-OFN (010) crystal plane and BGP-TBPA (002) crystal plane. (g) The XRD patterns of BGP-TBPA cocrystals, BGP-OFN cocrystals, and the corresponding OLHs. Download figure Download PowerPoint Scanning electron microscopy (SEM) was performed on the individual single-lateral OLHs (Figure 3e); the results suggested that the OLHs microwire had precisely defined materials and interfaces, with the short microwire corresponding to BGP-TBPA and the long microwire corresponding to BGP-OFN. The detailed SEM images of branch heterostructures at low and high magnification are shown in Supporting Information Figure S20. It is evident that the microwire branch of BGP-OFN grew on both the top and bottom surfaces of the trunk microwire of BGP-TBPA. We also prepared single-structures of BGP-TBPA and BGP-OFN. We found that the length-diameter ratio of the BGP-TBPA microwire was smaller than that of the BGP-OFN microwire ( Supporting Information Figure S19), which was also observed in the predicted growth morphologies of BGP-TBPA and BGP-OFN single crystals ( Supporting Information Figure S29). As we all know, well lattice matching plays a vital role in the epitaxial growth processes of heterostructures, enabling a periodic reconstruction of the interface. To better understand the growth mechanism of the [email protected] branch heterostructures, we calculated the growth morphologies and other parameters of BGP-TBPA and BGP-OFN cocrystal by Materials Studio simulation. As shown in Figure 3f, the BGP-TBPA backbone grew along the a-axis and came in contact with the BGP-OFN microwire with its (002) plane (represented by the orange area), while the BGP-OFN branch microwire grew along the a-axis and came in contact with the BGP-TBPA backbone with its (020) plane (represented by the blue area). Importantly, it is apparent that the (002) plane of BGP-TBPA and (020) plane of BGP-OFN had a low lattice mismatch ratio (n) of 0.7%, which facilitated the formation of branch microwires. Moreover, the XRD patterns of the branch heterostructure microwires only included the characteristic diffraction peaks of both BGP-OFN and BGP-TBPA without new emerging peaks (Figure 3g), which further confirmed that the branch heterostructures composed of BGP-TBPA trunk and BGP-OFN branches. Figure 4 | (a) Schematic diagram for the evolution process of [email protected] branch heterostructures convert to a series of branch heterostructures with different emission colors. (b1 and b2) FM images of [email protected] single-lateral and double-lateral heterostructures. (c1 and c2) FM images of [em