Strategies for the directional self-assembly of OSHsThe organic opto-functional molecules 4H-dithieno[3,2-b:2’,3’-d]pyrrole (HDP) and benzo[c]phenanthrene (BHT) display strong electron-donating abilities (Supplementary Fig. 1). With the combination of electron-deficient 1,2,4,5-tetracyanobenzene (TCNB) molecules through charge-transfer (CT) interactions, HDP self-assembled into 1D red-emitting TDP microrods with a photoluminescence (PL) peak at 750 nm (Figs. 1c, g, and Supplementary Fig. 2). The calculated molecular orbitals (MOs) of the TDP cocrystal are completely different from those of the independent TCNB and HDP molecules. Specifically, the energy diagram shows that the highest occupied molecular orbital (HOMO) ( − 5.60 eV) of the TDP cocrystal is lower than that of the isolated HDP molecule ( − 5.15 eV), while the corresponding lowest unoccupied molecular orbital (LUMO) ( − 3.70 eV) is greater than that of the isolated TCNB molecule ( − 3.92 eV). This could be ascribed to the transfer of π-CT from the HOMO of HDP to the LUMO of TCNB, causing the charge to interact in the ground state, rearranging electrons to form entirely new MOs (Supplementary Fig. 3)29. Additionally, the simulated crystallographic data revealed that the TDP crystal has cell parameters of a = 7.3528 Å, b = 7.1026 Å, c = 29.5733 Å, α = 90°, β = 90.347°, and γ = 90° (Supplementary Table 1), and belongs to the P21/c space group and monoclinic system.The BHT and TCNB molecules self-assembled into 1D green-emitting THT microrods (Figs. 1d, h, and Supplementary Fig. 2), and the PL peak was located at 560 nm. The lower HOMO energy ( − 5.86 eV) of the THT cocrystal than that of the BHT molecule ( − 5.54 eV) and the higher LUMO energy ( − 3.62 eV) compared to that of the TCNB molecule ( − 3.92 eV) indicate the formation of entirely new MOs (Supplementary Fig. 4). The THT cocrystal possesses cell parameters of a = 7.2363 Å, b = 8.0530 Å, c = 16.9259 Å, α = 88.451°, β = 89.127°, and γ = 87.740° and belongs to the Pī space group and triclinic system (Supplementary Table 2). The spatial PL spectra were adopted to calculate the CIE coordinates, which verified the fidelity of the emission colors in the fluorescence microscopy (FM) image (Supplementary Fig. 1), and the true emission colors of the TDP (0.72, 0.28) and THT (0.47, 0.51) microrods were obtained (Supplementary Fig. 5). These two TCNB-based cocrystals both present one-dimensional (1D) structural features with intense body emission. These as-fabricated TDP and THT cocrystals demonstrate PL lifetimes (τ) of 25.65 ns and 94.81 ns (Supplementary Fig. 6), respectively. Moreover, the photoluminescence quantum yields of 28.6% and 44.1% indicate superior optical performance.Transmission electron microscopy (TEM) investigation revealed that the TDP and THT microrods (Supplementary Figs. 7a, 8a) both present a typical 1D structure with straight and long morphologies, which is consistent with the calculated morphology (Supplementary Figs. 9, 10). Furthermore, the apparent diffraction spots in the selected-area electron diffraction (SAED) diagrams (Supplementary Figs. 7b, 8b) indicate that these two microcrystals are highly crystalline and grow in the same direction [100]. The intense diffraction peaks shown in the X-ray diffraction (XRD) patterns further verify the highly crystalline nature of the TDP and THT cocrystals (Supplementary Figs. 11). Furthermore, the polarization patterns of TDP and THT cocrystals with anisotropic properties also demonstrate high crystallinity (Supplementary Figs. 12). Notably, TDP and THT cocrystals possess similar molecular packing patterns (Supplementary Figs. 13, 14), indicating high structural compatibility30. On the strength of their structural advantages, TDP and THT cocrystals contribute to the hetero-nucleation and epitaxial growth to construct organic heterostructures.Nevertheless, the CT interactions of the TDP ( − 16.23 kcal mol−1) and THT ( − 18.43 kcal mol−1) cocrystals are approximately equal. Similar weak interactions are more conducive to driving homogeneous nucleation of individual cocrystals (Supplementary Figs. 15, 16) than hierarchical self-assembled heterostructures with precise spatial organization. Consequently, instead of a one-pot reaction, a multistep seeded self-assembly strategy is adopted to reasonably design and construct OSHs with precise spatial organization (Supplementary Fig. 17). Specifically, through a typical solvent evaporation method31,32, red-emissive TDP cocrystals are prepared and put into the system as preformed seed microrods. Then, green-emissive THT cocrystals are added for epitaxial growth on the preexisting TDP microrods. As a result, semi-wrapped or all-wrapped organic C/S heterostructures (Supplementary Fig. 18) are obtained by controlling the relative molar ratio of THT and TDP cocrystals. In detail, when the molar ratio of red-emitting TDP cocrystals to green-emitting THT cocrystals is 1:20, all-wrapped C/S heterostructures are formed, and when the ratio is 1:10, a certain amount of THT cocrystals only partially epitaxially grow on the TDP microrods, exposing the core part at the center of the microrods and forming the semi-wrapped C/S heterostructures (Figs. 1e, i, and Supplementary Fig. 19). In development, the aforementioned semi-wrapped C/S heterostructures are added as 1st layer building blocks to a TDP cocrystal-saturated supernatant, leading to the oriented epitaxial growth of TDP on the unwrapped core surface and eventually obtaining superimposed heterostructures with fixed interlayer positions on the c-axis (Figs. 1d, j).Construction of semi-wrapped C/S heterostructuresThrough a stepwise seeded self-assembly approach33, organic semi-wrapped C/S heterostructures are controllably fabricated after green-emissive THT cocrystals undergo selective heterogeneous nucleation and epitaxial growth on the surface of preexisting red-emissive TDP microrods. As illustrated in Fig. 2a, a certain amount of green-emissive THT cocrystals are only partially selectively wrapped on the prefabricated TDP microrods, causing the exposure of a portion of the core part. The presence of well-defined semi-wrapped C/S heterostructures is preliminarily confirmed by the FM image in Fig. 2b. The FM image of the representative organic semi-wrapped C/S heterostructure (Fig. 2c) indicates that under excitation in the UV band (330–380 nm), the middle segment output red emitting and both ends outcouple green emitting. Under the excitation of green-light (500–550 nm), the entire axis of the rod-like structure emits bright and clear red-emission (Fig. 2d). This excitation wavelength-dependent emission is ascribed to spectral overlap between the excitation source and the intrinsic excitation spectra of the THT cocrystal, which confirms the C/S structure at both ends and the exposed core in the middle.Fig. 2: Structure and growth mechanism of semi-wrapped C/S heterostructure.a Illustration of the growth process of organic semi-wrapped C/S microrods. b FM image of TDP microrods partly wrapped by THT cocrystals, scale bar: 20 μm. c, d FM images of an individual semi-wrapped C/S construction excited by (c) UV light (330–380 nm) and (d) green light (500–550 nm). Scale bars: 10 μm. e Bright-field micrograph of the corresponding semi-wrapped C/S heterostructure in c, scale bar: 10 μm. f SEM micrograph of a typical semi-wrapped C/S heterostructure with an obvious unwrapped gap. g Corresponding PL spectra obtained from the tip and body sites labeled in (c). h−j Molecular packing arrangements and lattice matching rate (η) of TDP and THT cocrystals at the (h tip, i side, and j upper) surface within the semi-wrapped C/S heterostructures.Moreover, an obvious heterojunction between the C/S block and unwrapped block is clearly observed in the bright-field image (Fig. 2e). Scanning electron microscopy (SEM) observation visually revealed the smooth surface of the C/S block and the growth gap caused by the incomplete package (Fig. 2f and Supplementary Fig. 20). The spatially resolved PL spectrum in situ collected at the end of the heterostructure (marked as 1 in Fig. 2c) by focusing a laser beam (λ = 380 nm) contains both green emission from the THT cocrystal and red emission from the TDP cocrystal (Fig. 2g), verifying the C/S block within the heterostructure. However, the PL peak in the middle part of the microrod (marked as 2 in Fig. 2c) only shows red emission from the TDP cocrystal, and the PL peak is located at 750 nm, convincingly demonstrating again that there is an unwrapped gap in the structure. Interestingly, the PL spectra at the tip position of the semi-wrapped C/S heterostructure exhibit a series of sharp fluorescence resonance peaks that indicate an optical cavity effect. This is because it contains a signal that resonates in the end part of the heterostructure. The cavity effect suggests the excellent light confinement property of the semi-wrapped C/S heterostructures, which is essential for the propagation of photon signals in optical circuits34. These PL spectra are consistent with those of the individual TDP and THT cocrystals depicted in Supplementary Fig. 2. The CIE coordinates obtained from the spectra of the C/S block (green line) and unwrapped core block (red line) are (0.52, 0.47) and (0.70, 0.27), respectively (Supplementary Fig. 21). Hence, organic semi-wrapped C/S heterostructures consisting of red-emissive TDP micro rods as the core and green-emissive THT cocrystals as the shell are successfully fabricated by controlling the relative molar ratio of TDP and THT cocrystals.Notably, the mechanism of the facet-selective epitaxial growth process driven by lattice matching and surface-interface energy balance to construct semi-wrapped C/S structures is investigated in detail. As depicted in Fig. 2h, the (100) crystal surfaces of the TDP cocrystal and THT cocrystal adopt similar molecular packing modes, contributing to the large lattice matching rate (η1 = 1 − | 7.35 − 7.23 | /7.35) of 98.37%, resulting in preferential epitaxial growth on the tip surfaces of the TDP microrod. Moreover, considering the surface-interface energy balance, THT molecules preferential hetero-nucleation at the (100) tip surface with the highest attachment energy in the TDP crystal ( | ETDPattach{100}s = −65.37| kcal mol−1 > | ETDPattach{011}s = −54.22| kcal mol−1 > | ETDPattach{002}s = −24.60| kcal mol−1) to eliminate unstable surfaces (Supplementary Table 3), achieving a thermodynamically favorable state35. Furthermore, the side surface of the TPD crystal adopts a low lattice mismatching rate (η2 = | 6.91 − 7.19 | /6.91 = 4.05%) with the side surface of the THT crystal (Fig. 2i), facilitating further epitaxial growth of the THT crystals. Moreover, the similar lattice constants (η3 = 1 − | 7.40 − 7.34 | /7.40 = 99.19%) of the upper crystal planes in the two growth morphologies are also beneficial for the epitaxial growth process (Fig. 2j). Nevertheless, the (001) upper surface of the TDP crystal possesses the lowest surface attachment energy (Supplementary Table 3), causing exposure of the upper surface in the case of insufficient THT molecules, i.e., unwrapped core blocking in the heterostructures.Directional self-assembly process of OSHsThen, the self-assembled high-energy metastable organic semi-wrapped C/S heterostructures act as building blocks for the further oriented homogeneous nucleation of TDP cocrystals. Specifically, these as-prepared semi-wrapped C/S heterostructures offer a high-energy unwrapped gap that facilitates the oriented self-assembly of organic molecules. As a result, when additional TDP molecules are added to the system of these as-prepared semi-wrapped C/S heterostructures, the TDP molecules preferentially undergo homogeneous nucleation at the unwrapped gap, eventually realizing organic superimposed heterostructures with fixed interlayer positions on the c-axis (Fig. 3a). As shown in Fig. 3b, the long microrod of the 1st layer exhibits yellow−green emission, which is consistent with the aforementioned semi-wrapped C/S heterostructure, and the short microrod of the 2nd layer exhibits red emission, which is consistent with the TDP cocrystal upon excitation with UV light. However, under the excitation of green light, the entire superimposed heterostructure exhibited bright and clear red emission (Fig. 3c). It is preliminarily proven that the formation of a superimposed heterostructure is based on the presence of a semi-wrapped C/S structure, which is further formed by an oriented self-assembly process in the unwrapped area. The bright-field and SEM images given in Figs. 3d, e intuitively display the heterojunction between the 1st layer and 2nd layer. Furthermore, the PL spectra of the long microrod (labeled as 1 in Fig. 3b) exhibit PL peaks at 560 and 735 nm, which is consistent with the PL spectra of the semi-wrapped C/S heterostructure (Fig. 3f). The short microrod (labeled as 2 in Fig. 3b) presents a PL peak at 750 nm, which is in accordance with the PL peak of an independent TDP crystal (Supplementary Fig. 2). Moreover, the PL spectra collected at the hetero-interface contain both green emission from THT and red emission from the TDP crystal, demonstrating that the superimposed heterostructures were successfully constructed.Fig. 3: Growth mechanism analysis and quantitative regulation of the OSHs.a Illustration of the oriented integrated process of OSHs constructed on the basis of semi-wrapped C/S heterostructures. b−d FM images of a typical superimposed heterostructure under the excitation of (b) UV and (c) green light. Scale bars: 10 μm. d Bright-field micrograph of the corresponding OSH, scale bar: 10 μm. e SEM micrograph of a typical OSH. f Corresponding PL spectra gathered at different positions labeled in b. Inset: the corresponding polar image of the peak intensity. g Molecular packing arrangement and direction at the heterojunction area of the superimposed heterostructure. h SEM image of a typical heterojunction area within an OSH. i TEM micrograph of an individual OSH. j, k SAED patterns of the (j) 2nd layer and the (k) 1st layer within the superimposed structure. l FM images of organic superimposed heterostructures with increasing red region length from left to right. m Plot of the length ratio for the red part within the whole structure versus the molar ratios of TDP and THT cocrystals.Significantly, the contact surface with the same packing arrangement and orientation between the 1st and 2nd layers contributes to a 100% lattice matching rate (Fig. 3g), revealing the tendency for these two layers to exhibit an oriented combination. Notably, the interlayer position control is induced by unwrapped growth gaps within the semi-wrapped C/S heterostructure, rather than the 100% lattice matching mentioned above. The semi-wrapped C/S heterostructures, as a kind of high−energy metastable structure, induce the preferential nucleation of molecules at the growth gap to eliminate unstable surfaces, achieving a thermodynamically favorable state. An ultralow lattice mismatch ratio below 5% is a prerequisite for the construction of heterogeneous structures. Therefore, the oriented growth process can be theoretically realized by selecting materials with lattice matching rates greater than 95% with the exposed core part.As illustrated in Fig. 3h, as the 1st layer of the OSHs, the semi-wrapped C/S heterostructure has an obvious groove, providing a preferential nucleation site for the growth of the 2nd layer structure. The TEM image (Fig. 3i) clearly shows a distinct superimposed heterostructure with disparate layer lengths, and the corresponding SAED spots (Fig. 3j) of the short microrod (marked as 1) present a pattern identical to that of the TDP microrod growing along the same direction as [100]. In contrast, the diffraction spots of the long microrod (marked as 2) are disordered (Fig. 3k). The disordered diffraction spots are attributed to the lattice superposition of the core section and shell section, which changes the molecular-stacking orientation. Moreover, the XRD pattern (Supplementary Fig. 11) of the superimposed structures contains the characteristic peaks of both TDP and THT cocrystals. These data successfully demonstrate the feasibility of utilizing semi-wrapped C/S heterostructures to induce the oriented self-assembly of OSHs with specific interlayer sites.Notably, the length of the 2nd layer (red part) within the OSHs is quantitatively adjusted by modulating the molar ratio of TDP to THT during the self-assembly process of the 1st layer. Take an example, a 100 μL TDP mixed solution with a concentration of 2.0 mmol L−1 was dropped on a quartz substrate, and after the crystallization time was 60 s, a 1500 μL THT mixed solution at a concentration of 2.0 mmol L−1 was dropped onto a quartz substrate with crystallized TDP cocrystal. When the crystallization time reached 60 s, 350 μL of the TDP mixed solution was dropped onto the substrate again, and when the solvent evaporated completely, organic vertically superposed heterostructures with a length ratio of 21.7% were observed. For another example, a 100 μL TDP mixed solution was dropped on a quartz substrate, and after the crystallization time was 60 s, 300 μL of the THT mixed solution was dropped onto a quartz substrate with a crystallized TDP cocrystal. When the crystallization time reached 60 s, 650 μL of the TDP mixed solution was dropped onto the substrate again, and when the solvent evaporated completely, vertically organic superposed heterostructures with a length ratio of 95.3% were observed.As shown in Fig. 3l, the length of the red-emitting 2nd layer is inversely proportional to the proportion of THT cocrystals. In fact, during the construction of the 1st semi-wrapped C/S heterostructures, the exposed degree of the core segment is increased or decreased by decreasing or increasing the proportion of THT cocrystals, respectively, thereby regulating the length of the 2nd layer in the superimposed heterostructures. As indicated in Fig. 3m, the length ratio of the 2nd layer linearly depends on the ratio between the TDP and the THT cocrystal. Consequently, according to this linear relationship, the relative length ratio from 21.7% to 95.3% of the different layers in the superimposed structure can be reasonably controlled by accurate quantitative manipulation of the ratio of TDP to THT crystals.Application of photonic barcodes in OSHsThe heterojunction interface of organic heterostructures is the key component for photon input and output in modern optoelectronics36, as in the case of photonic switches37,38, optical routers39,40, and wavelength converters41. Significantly, the coupling of excitons and photons is an effective approach for regulating the optical transmittance of organic active waveguides at low power density42,43. As shown in Fig. 4a, the greater energy gap of green-emissive THT cocrystal than that of red-emissive TDP cocrystal is conducive to the energy transfer (ET) process from THT to TDP cocrystals. Moreover, the close coincidence of the THT emission spectra and TDP absorption spectra (Supplementary Fig. 2) indicated that energy transfer could occur via either the short-range Dexter mechanism ( < 1 nm) or the long-range Förster resonance energy transfer (FRET) process. However, the short-range Dexter mechanism could not account for the current system, which shows a high energy transfer efficiency at an almost negligible TDP doping ratio, indicating long-range energy transfer. The energy transport by excitons in these as-prepared organic superposed heterostructures mainly involves a FRET process based on dipole−dipole coupling, which is ascribed to a long-range energy transfer process44.Fig. 4: Optical barcode operation of OSHs.a Illustration of the optical transport behaviors within OSHs and the ET process from green-emissive THT to red-emissive TDP crystals. b, c FM images of the organic superimposed heterostructure excited by a focused laser at different sites and the corresponding PL intensity of the optical signal extracted by MATLAB software. d, e Spatially resolved PL spectra of four output channels (O) corresponding to the (d) input I (In I) and (e) input II (In II) channels, as marked in (b and c), respectively. Inset: the corresponding polar image of the peak intensities. f Illustration of the coding rule of the photonic barcode. g The barcodes of the organic superimposed heterostructure corresponding to (d and e).As shown in Supplementary Fig. 22, when combined with the TDP cocrystal, the PL lifetime of the THT cocrystal at 560 nm is significantly reduced from 94.81 to 70.07 ns. Comparatively, the PL lifetime at 750 nm of the TDP cocrystals markedly improved from 25.65 to 34.15 ns after the formation of the heterojunction. The decrease in the PL lifetime of the THT cocrystal occurs because of the increasing density of low-energy states for energy migration, i.e., the increase in TDP cocrystals whose PL decay is faster when energy transfer occurs in heterostructures. The increase in the PL lifetime of TDP is attributed to the increased contribution of the THT cocrystals, whose PL decay is substantially slower45. The wavelength-dependent changes in the emission lifetime suggest effective energy transfer efficiency at 560 nm and 750 nm, indicating the involvement of exciton migration in the energy transfer process46. Therefore, the excited excitons of the THT shell layer can be effectively transferred to the TDP core layer through an energy transfer process, resulting in orange emission (Fig. 4a).Subsequently, the optical waveguide behaviors of TDP and THT cocrystals were measured via homemade optical microscopy (Supplementary Fig. 23). In detail, bright green and red emissions are observed at the tips of the THT and TDP microrods, respectively, with a 380 nm laser beam locally excited along the axis of the organic microrods (Supplementary Fig. 24a, d). Accordingly, distance-dependent PL spectra are collected from the tips (Supplementary Fig. 24b, e), demonstrating that the PL intensity at the tip decreases gradually with increasing photon transmission distance. Furthermore, the optical-loss coefficients of single THT and TDP microrods (RTHT = 0.174 ± 0.003 dB/μm, RTDP = 0.130 ± 0.004 dB/μm) are calculated using a single-exponential fitting Itip/Ibody = Aexp( − Rd)47, where d represents the distance between the excitation point and emission tip. The low optical loss coefficients demonstrate the excellent photon confinement ability and good optical waveguide performance of these two TCNB-based cocrystals.Organic superimposed heterostructures composed of a TDP-THT semi-wrapped C/S heterostructure (1st layer) and a single TDP microrod (2nd layer) were prepared for the exploration of optical transmission behavior at the heterojunction. Accordingly, prototypical photonic barcodes based on an individual organic superimposed heterostructure have been proposed. As shown in Fig. 4a, four optical output channels are located on the two tips of the 1st layer and the 2nd layer. When excited at the center part of the 1st layer (Input I), the photon transmission to the 1st layer corresponds to the passive waveguide mode48, leading to the spectra and polarizations at all channels being the same as those at the excitation positions (Figs. 4b, d). Moreover, the red luminescence at both tips of the 2nd layer structure displays an active optical waveguide mode with discrepant PL spectra and polarizations between the excitation position (Figs. 4b, d), indicating that the excitons of the THT are generated and that energy is transferred to the TDP during optical transmission via a FRET process. In contrast, when the 2nd layer (Input II) is excited, the passive waveguide mode causes the four channels in both the 1st and 2nd layers to produce spectra and polarization identical to those of the excitation positions (Figs. 4c, e). Hence, in the absence of the FRET process, red emission is observed in all channels of the 1st layer and 2nd layer in the superimposed heterostructure. Notably, the photon efficiency is calculated based on the output couple spectrum and in situ spectrum47. The efficiencies are calculated to be 93.8% and 89.2% when excited at In1 and In2, respectively. The high photon efficiency further reveals the low optical loss, which promotes the development of nanophotonic integrated optoelectronics.For potential photonic applications, a multichannel information encoding function is achieved according to the obviously different emission and polarization signals. As shown in Fig. 4f, the output channels (O1-O4) on the left side of the horizontal coordinate correspond to input mode I, and the four output channels (O1’-O4’) on the right side correspond to input mode II. Moreover, the vertical coordinate represents the wavelength and intensity of the PL emission and the angle and intensity of the polarization. Then, the excitation position-dependent waveguides that flexibly regulate the emission and polarization of the different output channels are collected as photonic barcodes. These optical parameters of the vertical axis represent two types of logical values, i.e., 0 and 1. In detail, the same PL spectral wavelength of both the output channel and excitation position is defined as 1, and conversely, it is defined as 0. Analogously, if the PL spectral intensity of the output signal is (or is not) greater than half of the PL spectral intensity of the excitation position, the output signal is considered to be 1 (0). Furthermore, a polarization output signal > 90° relative to the rod direction is defined as 1, and conversely, is regarded as 0. For the polarization intensity, the output signal could be defined as 1 (0) when the lowest intensity is less (greater) than 50% of the highest intensity. These output values are filled based on the logical code of the signal from the output channels. Accordingly, photonic barcodes are achieved by summarizing the output signals of multiple output channels in the superimposed heterostructure (Fig. 4g). Consequently, optical interconnection heterostructures with anisotropic properties contribute to accurate regulation of optical signals within multiple input/output channels and promote the development of 2D photonic encryption devices.
