Pyrene-based conjugated porous polymers as photocatalysts for oxidative cycloaddition of phenols

Abstract

Photocatalytic heterogeneous organic transformation represents an ecofriendly and sustainable method for addressing persistent energy and environmental challenges. Conjugated porous polymer (CPP)-based materials have recently emerged as promising photocatalysts for diverse organic transformations, offering a sustainable alternative to homogeneous systems reliant on precious inorganic or organic dyes. Herein, we designed two pyrene-based CPPs for visible-light photocatalysis, featuring fluoro- or methyl-substituted fluorenes as distinct units. These CPPs act as metal-free, visible-light-activated, reusable heterogeneous photocatalysts for synthesizing benzofused oxa-heterocycles via photooxidized [4 + 2] and [3 + 2] cycloadditions of phenols with alkenes. Notably, DFT calculations demonstrate that the fluoro-block CPP with its larger dipole moment can achieve more efficient photoinduced charge separation, due to the stronger electron-attractive force. Consequently, FF-Py-CPP exhibited superior photocatalytic activity compared to MF-Py-CPP, achieving excellent yields, high diastereoselectivity, and good recyclability in the syntheses of chromanes and dihydrobenzofuran.