Enhanced photostability in protonated covalent organic frameworks for singlet oxygen generation

Covalent organic frameworks (COFs), highly ordered, functional porous crystalline polymers, have found prospective applications in heterogeneous catalysis. Owing to unique fully π-conjugated sp2 carbon structures, vinylene-linked CO-Fs provide an extraordinary platform to develop photocatalysis, while they suffer from serious photo-instability during catalysis, hindering widespread applications. Here, by taking g-C18N3-COF as a prototypical system, we propose that protonation endows it with enhanced photostability by impeding the flow of band electrons, meanwhile light absorption was extended to long wavelength and separation of photocarriers is facilitated. Both structural and spectroscopic results demonstrated the greatly improved photostability of protonated g-C18N3-COF, which can keep the vinylene-linked framework for a long time under visible light irradiation. Benefiting from the above merits, the protonated g-C18N3-COF was an efficient catalyst for singlet oxygen generation by two sequential charge transfer processes. This work provides a practical approach to enhance the photostability and catalytic activities of vinylene-linked CO-Fs and its derivatives.