Novel Triangulenes: Computational Investigations of Energy Thresholds for Photocatalytic Water Splitting.

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Abstract

Organic materials with Inverted Singlet-Triplet (INVEST) gaps are interesting for their potential use as photocatalytic small molecule transformations, like the entirely solar-driven water splitting reaction. However, only few INVEST emitters are thermodynamically able to split water, with first singlet excited states, S1, above 1.27 or 1.76 eV; and absorbing near solar maximum, 2.57 eV. These requirements and the INVEST character are key for achieving long-lived photocatalyst for water splitting. The only known INVEST emitters that conform to these criteria are large triangular boron carbon nitrides, with unknown synthesis pathways. With quantum-mechanical calculations using ADC(2), we describe three triangulenes. 3a is a cyano azacyclopenta[cd]phenalene derivative while 3b and 3c are cycl[3.3.3]azine derivatives. 3b has a previously undescribed disulfide bridge. Overall 3a fulfills requirements for photocatalytic four-electron reduction of water while the S1 states of 3b and 3c are likely slightly low for the two-electron reduction process. By analyzing impacts of ligands, we find that there are guidelines describing how S1-S5 energies and oscillator strengths, T1 energies and ΔES1T1 gaps are affected, requiring deep-learning algorithms for which studies will be presented by us in due time. The impact of solvation effects as well as reduced-cost ADC(2) algorithms on our findings are discussed.© 2023 Wiley-VCH GmbH.