Polymer Connectivity Governs Electrophotocatalytic Activity in the Solid State

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Abstract
The reductive functionalization of inert substrates like chloroarenes is a critical yet challenging transformation relevant to both environmental remediation and organic synthesis. Combining electricity and light is an emerging approach to access the deeply reducing potentials required for single electron transfer to chloroarenes, yet this approach is held back by the poor stability and mechanistic ambiguity of current homogeneous systems. Incorporating redox-active moieties into insoluble organic materials represents a promising strategy to unlock new heterogeneous catalytic activity while improving catalyst stability. Herein, we demonstrate the first example of heterogeneous electrophotocatalysis using redox-active rylene diimide polymers for the reduction of chloroarenes. In particular, we find that the electrophotocatalytic activity varies significantly not just as a function of the rylene diimide but also of the redox-inactive polymer backbone. In particular, PTCDA-en, a flexible, non-conjugated perylenediimide polymer, outperforms all other tested materials as an electrophotocatalyst. Using transient absorption spectroscopy, we reveal that precomplexation between the closed-shell PTCDA-en2− and the haloarene substrate is key to productive catalysis. Overall, our work represents the first example of heterogeneous electrophotocatalysis using an insoluble redox-active organic material and provides critical insights into how polymer structure dictates electrophotocatalytic activity in the solid state, guiding the development of next-generation heterogeneous (electro)photocatalysts for sustainable synthesis.

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