The Role of Computational Chemistry in Discovering and Understanding Organic Photocatalysts for Renewable Fuel Synthesis

Abstract

In this review the role computational chemistry plays in helping to rationalize the ability of organic materials, such as conjugated polymers, to drive photocatalytic water splitting and CO2 reduction, and the discovery of new organic photocatalysts, is reviewed. The ways in which organic photocatalysts differ from their inorganic counterparts, the mechanism by which such materials, when illuminated, reduce protons or CO2 and oxidize water or sacrificial donors, and how this can be studied using computational methods, as well as the high‐throughput virtual screening of organic materials as photocatalysts, are discussed. Finally, the current opportunities and challenges associated with studying photocatalysts computationally, are examined.

Water Oxidation and Hydrogen Evolution with Organic Photooxidants: A Theoretical Perspective

“…Already in the early 1990s, Yanagida and co-workers reported hydrogen generation with poly­( p -phenylene) and poly­(pyridine–diyl) polymers in the presence of a dispersed noble-metal cocatalyst and a sacrificial electron donor. , More recently, the hydrogen evolution reaction with organic polymer photocatalysts was systematically explored by Cooper and co-workers. ,, Like in the polymeric carbon nitride materials, the photocatalytic mechanisms in these materials are currently poorly understood. Prentice and Zwijnenburg recently discussed the pros and cons of the charge-carrier mechanism and the radical-pair mechanism in conjugated polymers. , Evidence has been reported that conjugated polymers containing N-heterocycles are superior photocatalysts and that the hydrogen evolution yield seems to increase with the nitrogen content. − Moreover, it has been observed that small oligomers seem to be more efficient photocatalysts than extended polymers of the same material . These findings are hints that photooxidation of the substrate at local nitrogen centers may play a role in the photocatalysis.…”

“…Prentice and Zwijnenburg recently discussed the pros and cons of the charge-carrier mechanism and the radical-pair mechanism in conjugated polymers. 81,82 Evidence has been reported that conjugated polymers containing N-heterocycles are superior photocatalysts and that the hydrogen evolution yield seems to increase with the nitrogen content. 83−85 Moreover, it has been observed that small oligomers seem to be more efficient photocatalysts than extended polymers of the same material.…”

From monomer sequence to charge mobility in semiconductor polymers via model reduction

“…Over the years, semiconducting organic polymers have evolved as the active-layer materials in a range of technological applications like field-effect transistors (OFET), 1,2 light-emitting diodes 3 and organic photovoltaic devices. 4 Despite of these large number of current as well as proposed technological applications like in photocatalytic, 5,6 thermoelectric, 7,8 bioelectronic 9 and neuromorphic devices, quantitative models that link the chemical structures of the conjugated polymers with their charge-carrier mobilities are not yet available. The charge-carrier's motion in polymeric semiconductors is a complex process [10][11][12] due to the anisotropy of charge transport along the chain (intra-chain transport) from that between neighboring chains (inter-chain transport).…”

The potential scarcity, or not, of polymeric overall water splitting photocatalysts

“…18 Conceptually, in the case of materials with a non-negligible exciton binding energy we need to consider besides IP and EA also IP* and EA*, the ionisation potential and electron affinity of the excitons, respectively. 19,20 This would allow us to describe exciton dissociation on the polymer particle–solution interface, where the exciton donates an electron or hole to drive one of the solution half-reactions, after which the other component of the exciton remains on the particle to take part in another solution half-reaction at some later point. However, in practice when screening materials the effect of the exciton binding energy, typically 0.1–0.2 eV 18 can be absorbed in a requirement for a similar overpotential on top of the thermodynamic solution potentials, meaning that the computationally expensive calculation of IP*/EA* can be avoided.…”