Chiral Cross-Linked Covalent Organic Framework Films for Highly Sensitive Circularly Polarized Luminescence Probing

The development of covalent organic framework (COF) films featuring circular polarization luminescence (CPL) probing remains a formidable challenge. Herein, we developed a chiral cross-linked COF film to obtain uniform and dense chiral COF films (chirCOFilm) possessing highly sensitive CPL probing for enantiomers. The axial chiral cross-linkers (R-/S-BBNA) are initially introduced into the channels of a COF film (COFilm/R-BBNA or COFilm/S-BBNA) by the vapor-assisted epitaxial method. Then, olefin groups in R-/S-BBNA and COF layers undergo a chiral cross-linking reaction under UV irradiation, forming a chirCOFilm. The obtained chirCOFilms have strong chirality with mirror images, fluorescence discoloration, and intense CPL properties. A multitude of rich chiral photopatterns and chirCOFilm/PDMS flexible films are prepared taking advantage of the photochromic properties of the chirCOFilms during UV illumination, showing the potential application of advanced anticounterfeiting. More importantly, the chirCOFilms realize highly sensitive CPL probing of phenethylamine enantiomers at 5% concentration, which can hardly be achieved from their corresponding fluorescence probing. This study not only provides a new strategy for preparing chiral COF films using chiral cross-linking reaction but also opens a new avenue for achieving highly sensitive probing of enantiomers though CPL.