Parallel syntheses were used to access 1,440 structurally highly diverse heteroleptic [Ir(C^N)2(N^N)]+ complexes where C^N stands for a large set of cyclometalating ligands and N^N for a family of 1,2-diimine chelators. Most of the complexes were found to be strongly luminescent (Figure), and the emission maxima of the library spanned the visible spectrum (652–459 nm) while the measured excited state lifetimes ranged between ∼0.1–14 μs. Electronic structure features obtained from DFT calculations performed on these Ir(III) chromophores offered clear insights into the excited state properties and allowed the prediction of structure/luminescence relationships in this class of widely used photocatalysts. Models with high prediction accuracy (R2 = 0.89) for emission color were developed on the basis of experimental data. Later, newly developed, massively parallelized reactors allowed the measurement of the photocatalytic activity of the studied [Ir(C^N)2(N^N)]+ complexes in the photoreduction of Sn(II) and Zn(II) cations to their corresponding neutral metals. Automated, kinetic data collection of these solar fuels relevant-processes gathered initial rates for the 1440 photocatalysts ranging between 0 – 120 μM/s for Sn(0) deposition and 0 – 90 μM/s for Zn(0) deposition. Interestingly, no correlation was found between the chromophore’s photophysical properties and its photocatalytic activity even when modern machine learning techniques were employed. A formal photochemical rate law was then developed to help elucidate the observed reactivity. Initial rates were found to be directly correlated to the product of incident photon flux with three reaction elementary efficiencies: (1) the fraction of light absorbed by the photocatalyst, (2) the fraction of excited-state species that are quenched by the electron donor, and (3) the cage escape efficiency.

Going with the glow: High-throughput screening and automated data-driven analysis of the photophysical and photochemical properties of phosphorescent Ir(III) Complexes

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.