Photoredox Chemistry with Organic Catalysts: Role of Computational Methods

Abstract

Organic catalysts have the potential to carry out a wide range of otherwise thermally inaccessible reactions via photoredox routes. Early demonstrated successes of organic photoredox catalysts include one-electron CO 2 reduction and H 2 generation via water splitting. Photoredox systems are challenging to study and design owing to the sheer number and diversity of phenomena involved, including light absorption, emission, intersystem crossing, partial or complete charge transfer, and bond breaking or formation. Designing a viable photoredox route therefore requires consideration of a host of factors such as absorption wavelength, solvent, choice of electron donor or acceptor, and so on. Quantum chemistry methods can play a critical role in demystifying photoredox phenomena. Using one-electron CO 2 reduction with phenylene-based chromophores as an illustrative example, this perspective highlights recent developments in quantum chemistry that can advance our understanding of photoredox processes and proposes a way forward for driving the design and discovery of organic catalysts.

Shining a Light on the Advances, Challenges and Realisation of Utilising Photoredox Catalysis in Pharmaceutical Development

“…Whilst further optimisation and scale up have not been reported, the initial results are encouraging and demonstrate successful use of organic PRCs in API development. Computational methods have a role to play in generating photophysical data for these compounds, allowing their rational design for pharmaceutical development applications [50] …”

“…With few published large‐scale reactions in the literature there is little reported precedent of suitable solvent, base and additive combinations for photoredox processes. Given that solvent choice greatly affects the photophysical properties of PRCs, [50] balancing conditions that give high yield and purity of the desired product with suitability for use in a manufacturing environment may ultimately result in a scaled‐up reaction outcome that demonstrates less benefit than on a small scale. As more data is collected in this sector regarding process monitoring (photon flux, quantum yields, productivity), energy saving, and maintenance issues, certainty in capital and operating expenses should increase [61] .…”

“…To alleviate many of the concerns associated with metalbased PRCs, organic photoredox catalysts [43] such as dyes [19,44] quinones, pyryliums, and phenylene derivatives [45] are being explored as viable alternatives. As with their metal-based counterparts, the properties of organic PRCs can be tuned to provide the desired photoreducing or photooxidising power and innately possess high stability against photodegradation.…”

“…Computational methods have a role to play in generating photophysical data for these compounds, allowing their rational design for pharmaceutical development applications. [50] Although the library of PRCs is continually expanding, key properties of these new catalysts are not consistently reported, hindering knowledge transfer between academic groups and industries. Several groups have taken steps to address this issue and have published detailed reports or reviews of solvent effects on PRC properties and mechanism, [51] solubility and stability of PRCs and electron transfer kinetics and quenching rates.…”

Simulating Excited-State Complex Ensembles: Fluorescence and Solvatochromism in Amine-Arene Exciplexes

“…[4][5][6][7][8][9][10][11][12] Such studies facilitate applications in organic light-emitting diodes (OLEDs) via thermally activated delayed fluorescence (TADF), [13][14][15][16][17] solar energy harvesting via singlet fission, [18][19][20] chemo-sensors for anion and cationic surfactant sensing [21][22][23][24][25] and bio-detectors, 26,27 and photoredox catalysis. [28][29][30] Advances in quantum chemistry methods have facilitated accurate modeling of excited states in isolated molecules as well as in the condensed phase. Excimer and exciplex structures have been computed by geometry optimization on excited-state potential energy sur-faces (PESs) using configuration interaction singles (CIS), 31 time-dependent density functional theory (TDDFT), 6,9,19,30,[32][33][34][35][36] equation-of-motion methods for electronically excited states based on coupled-cluster singles and doubles (EOM-EE-CCSD), 7 complete active space self-consistent field (CASSCF), and the algebraic diagrammatic construction scheme to second-order with resolution of identity and spin-opposite scale (RI-SOS-ADC(2)) methods.…”