Stepwise Epitaxial Growth of Core–Shell Organic Crystals for Advanced Dual-Emission Optical Applications

Organic core-shell heterostructures (CSHs) offer a unique platform for integrating complementary properties of the core and shell materials, leading to an optimized multifunctional performance. However, the growth mechanism within CSHs remains unclear due to the poor crystallographic compatibility between different components and fast crystallization. This study elucidates the detailed process for fabricating organic crystalline CSHs with tunable morphologies through an in situ epitaxial growth approach, by employing IDF-TCNB (Cry^DFNB) and IDT-TCNB (Cry^DTNB) charge-transfer cocrystals. After the lattice matching in three dimensions is satisfied, the shell Cry^DTNB epitaxially grows on the core Cry^DFNB surface along specific crystallographic orientations, with the growth sequence determined by differences in attachment energy. The unique bilayer structure of the CSHs results in distinct dual-emission optical properties, including differentiated polarization, dual-band quasi-whispering gallery mode resonance, and dual-band optical waveguides. This work provides a new framework for the design and synthesis of organic CSHs with controlled structures and advanced photonic functionalities.