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

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.

Computational design of boron-free triangular molecules with inverted singlet–triplet energy gap

“…10–12 Inverted singlet–triplet molecules also are of interest in photocatalysis, 13 for example for the photocatalytic water-splitting process. 14,15…”