Solid-State Fluorescence Enhancement In The Covalent Organic Cage Material Through Simple Grinding With Metal Salts: Chemo-Sensing And White-Light-Emitting Diode Applications.

Abstract

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