Highly Emissive Flexible Organic Crystals with Broad Piezochromism and Optical Waveguide s.

Abstract

The integration of mechanical flexibility with stimuli-responsive optical properties in organic single crystals (OSCs) remains a formidable challenge due to the intrinsic rigidity of π-conjugated systems. Herein, we report a rationally designed OSC, FBCF, that synergistically combines elastic deformability, broad piezochromism and low-loss optical waveguiding via a planar benzothiadiazole (BTA) core and fluoroarene termini. The molecular architecture enforces face-to-face slip-stacking via multiple noncovalent interactions (N···H, π-π, and C-F···π), yielding centimeter-scale crystals with exceptional elastic bending and full recovery. These crystals exhibit a high photoluminescence (PL) efficiency (PLQY = 75.8%) and serve as low-loss optical waveguides, maintaining performance even when bent (optical loss coefficients: 0.286-0.529 dB mm-1). Crucially, FBCF exhibits broad pressure-responsive spectral shifts (Δλ = 171 nm), achieving a piezochromic sensitivity of 16.7 nmGPa-1, exceeding that of most organic systems. Single-crystal X-ray diffraction analyses reveal hierarchical packing: rigid lamellar layers (stabilized by strong π-π/dipole interactions, ‑118.56 to ‑58.45 kcal/mol) interconnected via weaker interlayer C-F···π bonds (-18.8 kcal/mol). This architecture enables elastic deformation through interlayer slippage while preserving intralayer order.