Breaking of J‑Aggregates in Fluorescent Covalent Organic Cage Molecular Materials Through Solid State Grinding with Metal Salts: Chemo-Sensing and Light-Emitting Diode Applications

Covalent organic cages (COCs) show immense potential applications due to their structural flexibility and solution processability. Herein, we report an imine-linked [2 + 3] fluorescent COC (COC1) exhibiting fluorosolvatochromism in the solutions and green luminescence in the solid state. In the crystal, cage molecules form J-aggregates through van der Waals interactions. The C–H···π interactions within the crystal lattice have been disrupted by grinding the crystals with various inorganic metal salts. This disturbance introduces modifications in the crystalline structure through proposed C–H··· X^–(X = oxygen, halogen) interactions. In this context, the metal salt microcrystal surfaces served as a template for the cage molecules and acted as a “solid-state solvent” in a broad sense. Moreover, we have investigated the electroluminescence properties of the cage material, which showed green light emission upon coating the COC1-doped polymer film over the surface of a near-ultraviolet LED, and a thin layer of COC1 along with a red phosphor-doped polymer on the surface of a blue light-emitting diode (LED) resulted in a cool white LED. Furthermore, the cage material exhibited excellent acidochromic properties in the solid and solution states.