Quinoline-linked zwitterionic covalent organic frameworks: post-synthetic construction and mechanism-reversed third-order nonlinear absorption.

Quinoline-linked neutral TF-DA-Q and zwitterionic zi-TF-DA-Q covalent organic frameworks (COFs) were prepared via post-modification of imine COFs. The Polymethyl methacrylate (PMMA) composite films prepared for third-order nonlinear optical (NLO) measurements undergo a transition from reverse-saturable absorption (RSA) to saturable absorption (SA) after ionization modification.