Interfacial polarity-driven self-assembly of organic core/shell heterostructures with directional Fabry-Pérot resonance

Abstract

Organic core/shell heterostructures (OCSHs) can exhibit diverse optical functionalities through molecular-scale energy-level modulation and interface engineering. However, the construction of structurally well-defined, optically responsive OCSHs with ordered interfaces remains a significant challenge. Here, we proposed an interfacial polarity-driven self-assembly strategy to achieve the directional construction of OCSHs comprising a charge-transfer (CT) cocrystal core and an alloy shell. Selective interfacial complexation and polarity-driven molecular coupling were achieved by sequentially introducing CT cocrystals with gradient intermolecular interaction strengths, thereby disrupting the intrinsic growth pathway of the core and triggering directional alloying of the shell. The resulting OCSHs exhibit highly ordered Fabry-Pérot (FP) cavity modes and orientation-dependent emission, enabling multistate optical logic encoding. Moreover, the approach exhibits broad applicability across multiple CT pairs, affording structurally integrated heterostructures with tunable dual-emission profiles and potential for white-light emission. This work provides a robust framework for constructing hierarchical organic photonic architectures and programmable light-manipulation systems via interfacial interaction engineering.

Fig. 1. Description of directional self-assembly strategy for OCSHs. (a) Schematic illustration of interfacial polarity rearrangement-induced directional self-assembly proposed in this study. (b–d) FM images of (b) TBA, (c) TBB microrods and (d) organic core/shell heterostructures. Scale bars: 50 μm.

Fig. 2. Optical and polarized emission characterization of OCSHs. (a–c) FM images of a single OCSH under (a) UV, (b) blue light, and (c) bright-field excitation, corresponding to 330–380 nm and 460–490 nm for (a) and (b). (d₁) SEM image of the corresponding OCSH. (d₂ and d₃) The corresponding energy-dispersive X-ray spectroscopy (EDX) maps for C and N elements. (e) Micro-region PL (μ-PL) spectra obtained from various designated spots on the OCSH under λ = 395 nm excitation. Inset: related polar diagrams of the emission peak intensities. (f) Contour maps of polarization-resolved PL spectra obtained from the core and shell regions of heterostructure. (g) Polar plots of polarization-dependent emission intensities extracted from the core and shell regions. (h) The orientation of TDMs on the TBA (100) and TBB (011) crystal planes. (i) Top: schematic illustration of light paths in FP mode of OCSH. Bottom: simulated electric field distribution in the cavity. (j) μ-PL spectra collected along the long axis of the heterostructure. Top left: FM image of heterostructure showing the signal collection positions. Bottom right: simulated electric field propagation and standing wave patterns within the OCSH. (k) Linear relationship between the cavity length and the resonance peak spacing near 579 nm. All scale bars are 20 μm.

Fig. 3. Crystal analysis and theoretical calculations. (a) Molecular packing model at the core/shell interface. (b and c) Hirshfeld surfaces of TBA and TBB, mapped with electron density. (d and e) 2D fingerprint plots of TBA and TBB. (f and g) RDG functions and Sign(λ₂)ρ scatter plots of TBA and TBB.

Fig. 4. Optical logic response in core/shell heterostructures. (a) Schematic illustration of light propagation and ET processes within OCSHs. (b–d) FM images of heterostructure under focused laser excitation at different positions, with corresponding spatial intensity maps of emitted light. Scale bars: 20 μm. (e–g) Spatially resolved PL spectra were recorded from both excitation and output regions under different excitation sites. Insets: corresponding polar plots of peak emission intensities. (h) Summary table of the optical logic responses exhibited by OCSHs.

Fig. 5. Universality of interfacial polarity-driven self-assembly strategy. (a) Depicted molecular structures of the donor (1–5) and acceptor (6) species. (b–e) FM images of OCSHs constructed from different combinations of organic CT cocrystals. (f) Comparison of the noncovalent interaction strengths between the core and shell cocrystals in various OCSHs. Scale bars: 20 μm. (g) Spatially resolved μ-PL spectra collected from the core and shell regions of various heterostructures. (h) CIE chromaticity diagrams corresponding to the emission positions shown in (g).