Poly(arylene-ethynylene)s in Synthetic Heterogeneous Visible Light Photocatalysis: Structure-Reactivity Principles and Opportunities in Flow.

Visible light photocatalysis has reshaped synthetic organic chemistry by enabling mild and selective radical processes. However, its widespread adoption is still constrained by the reliance on homogeneous photocatalysts, typically precious-metal complexes or organic dyes, which complicate recovery, recyclability, scalability, and integration into telescoped continuous flow processes. Heterogeneous photocatalysts (hPCs) offer a sustainable alternative, and among emerging candidates, π-conjugated polymers (π-CPs) have recently attracted attention as tunable, metal-free semiconductors capable of efficient visible light harvesting. This perspective highlights poly-(arylene-ethynylene)-s (PAEs), a distinctive subclass of π-CPs whose modular, conjugated backbones enable control over morphology, band structure, and excited-state behavior. Historically developed for optoelectronic applications, PAEs are now gaining traction as photocatalysts in synthetic organic chemistry, including in continuous flow reactors. Yet, the absence of systematic structure-reactivity relationships limits rational catalyst design and restricts broader deployment. Here, we examine emerging trends that link PAEs structure to photocatalytic function and articulate guiding principles for designing next-generation polymeric photocatalysts. By integrating concepts from materials science and synthetic methodology, this perspective aims to establish PAEs as robust, recyclable, and versatile platforms for sustainable photocatalysis.