A theoretical perspective on charge transfer in photocatalysis. The example of Ir-based systems

•This review considers the theoretical treatment of charge transfer processes.•Special attention is paid on long-range corrected density functional theory.•The topic is illustrated using the example of an Ir-based photocatalytic cycle..•The elementary steps are discussed from the theoretical and experimental viewpoint.

Research on photocatalytic water splitting is a rapidly developing area, holding the promise to transform solar energy into chemical form that can be stored and reused on demand. Existing photocatalytic systems or dye-sensitized solar cells exploit a charge separation mechanism occurring upon photoexcitation. Along with the numerous experimental studies, theoretical simulations are performed to assist the interpretation of experimental data and the rational design of new environmentally benign systems. However, the accuracy of the theoretical results should be judged carefully since charge transfer processes represent a challenge at least for the widely used time-dependent density functional theory.In this review, we address the state-of-the-art of homogeneous photocatalysis based on noble metal photosensitizers from the quantum chemistry viewpoint. Exemplarily, we focus on a system with an iridium(III) photosensitizer, triethylamine as sacrificial reductant, and an iron carbonyl based water reduction catalyst. In addition, we consider the possible venues of improving the efficiency of solar light collection by introducing silver nanoparticles into the system. The applicability of various single- and multi-reference wave-function methods and especially of the optimally tuned long-range corrected density functional theory for the prediction of electronic spectra and intermolecular charge transfer probabilities is discussed.

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