Beyond porosity: emerging design principles in photocatalytic polymers for organic synthesis

Photocatalytic polymers have emerged as promising materials for the synthesis of high-value chemicals through photoredox transformations. Over the past few decades, a wide range of polymer architectures have been developed, spanning linear polymers to conjugated polymer networks. Porous polymer networks were initially designed to maximise photocatalytic performance by increasing surface area and, consequently, the number of accessible reactive sites. However, recent studies, including our own, have demonstrated that porosity is not a prerequisite for high photocatalytic activity. In porous materials, a significant fraction of reactive centres can reside within the bulk of the network, where they can be inaccessible to substrates, creating a "dead zone". The extent of this inactive region is governed by factors such as exciton diffusion length, substrate mass transport into the material, and diffusion rates within the pores. Consequently, photocatalytic reactions often predominantly occur at or near the material surface, limiting the benefits of internal porosity. This feature article therefore addresses a key question: what alternative design principles should be prioritised instead of porosity to maximise photocatalytic efficiency? Specifically, in this review I will discuss approaches to enhance the accessibility of reactive sites and improve charge-carrier generation, separation, and transport. Highlighting how these material design parameters can be systematically tuned to maximise photocatalytic reaction rates and overall performance.