Covalent Organic Framework for Improving Near-Infrared Light Induced Fluorescence Imaging through Two-Photon Induction

摘要

Fluorescent materials exhibiting two-photon induction (TPI) are used for nonlinear optics, bioimaging, and phototherapy. Polymerizations of molecular chromophores to form pi-conjugated structures were hindered by the lack of long-range ordering in the structure and strong pi-pi stacking between the chromophores. Reported here is the rational design of a benzothiadiazole-based covalent organic framework (COF) for promoting TPI and obtaining efficient two-photon induced fluorescence emissions. Characterization and spectroscopic data revealed that the enhancement in TPI performance is attributed to the donor-pi-acceptor-pi-donor configuration and regular intervals of the chromophores, the large pi-conjugation domain, and the long-range order of COF crystals. The crystalline structure of TPI-COF attenuates the pi-pi stacking interactions between the layers, and overcomes aggregation-caused emission quenching of the chromophores for improving near-infrared two-photon induced fluorescence imaging.