Nonlinear optical switching in regioregular porphyrin covalent organic frameworks

Covalent organic frameworks (COFs) have aroused immense scientific interest as an exhilarating class of porous materials due to their structure tunability and diverse properties. However, understanding of their response towards laser induced nonlinear optical (NLO) applications is in its infancy and demands prompt attention. Herein, we report three novel regioregular porphyrin based porous COFs, Por‐COF‐HH and its dual metalated congeners (Por‐COF‐ZnCu and Por‐COF‐ZnNi) with excellent NLO properties. Notably, intensity dependent NLO switching behavior was observed for these Por‐COFs, which is highly desirable for optical switching and optical limiting devices. Moreover, the efficient π‐conjugation and charge transfer transition in ZnCu‐Por‐COF enable a high nonlinear absorption coefficient (β=4470 cm/GW) and figure of merit (FOM = σ1/σo, 3565) values compared to other state‐of‐art materials including molecular porphyrins (β=~100‐400 cm/GW), metal‐organic frameworks (MOFs; β=~0.3‐0.5 cm/GW) and graphene (β=900 cm/GW)