Distortion Evolution of Two-Dimensional Molecular Crystals for Branched Optical Waveguides

Two-dimensional (2D) molecular crystals with irregular morphologies are promising candidates for constructing multifunctional optoelectronics. However, the impact of crystal distortion on morphological irregularities has been largely overlooked, despite its potential for engineering crystal structures with superior functionalities. Here, we report a competitive facet-selective growth strategy for synthesizing 2D molecular crystals with irregular morphologies, ranging from rhombus sheets to distorted compass shapes. Limited material availability makes deposition dominant on crystal facets with high attachment energy, thus driving a progressive structural distortion of microcrystals, evolving from compass shapes to branched wires. The resulting rhombus microsheets exhibit 2D optical waveguides with low-loss properties of 0.02 dB/μm, while the compass sheets enable focused directional emission. Importantly, the fabricated T-like branches with bidirectional waveguides are applied to a complex photonic switching device under dual-beam excitation. This work provides insights into the synthesis of unusual crystals and the development of next-generation optoelectronics.