The establishment of chiral COF films is still a hard bone. The development of chiral cross-linking reactions that integrate chirality with COF films through cross-linking reactions, to produce chiral COF films, represents a highly promising avenue, but has yet been reported. Circular polarization luminescence (CPL) as a kind of chiral optical property pertained to the excited-state chirality of chiral emitters. So far very few example of chiral COFs have been prepared for CPL performance by directly synthesis of chiral synthesis and chiral induced strategy. To enhance the convenience and broaden the practical use of chiral COFs for CPL applications, the development of chiral COF films for CPL probing is very important, but remains a formidable challenge.
In a study published in J. Am. Chem. Soc., Prof. ZHANG Jian, Prof. GU Zhigang and their colleagues from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences have reported chiral cross-linked covalent organic framework films for highly sensitive circularly polarized luminescence probing.
The researchers developed a chiral cross-linked COF film. The axial chiral cross-linkers (R-/S-BBNA) was initially introduced into the channels of COF film (COFilm/R-BBNA or COFilm/S-BBNA) by 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 chirCOFilm have strong chirality with mirror images, fluorescence discoloration and intense CPL properties.
A multitude of rich chiral photopatterns were prepared taking advantage of the photochromic properties of the chirCOFilm during UV illumination, showing the potential application of advanced anti-counterfeiting.
Moreover, the researchers prepared chirCOFilm/PDMS flexible films, to further expand the practical application in large-sized and flexible sensors. The chirCOFilm/PDMS flexible films boast excellent transparency, stability, and ease of operation, positioning them as potential candidates for applications in the optical sensor and device.
The chirCOFilm has strong chirality and evident intense CPL signal at 407 nm with |glum| of 2.16×10-3. More importantly, the chirCOFilm realized 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.
Schematic illustration of the research. (Image by ZHANG's group)
Contact:
Prof. GU Zhigang
Fujian Institute of Research on the Structure of Matter
Chinese Academy of Sciences
E-mail: zggu@fjirsm.ac.cn
