Visible‐Light‐Driven Hydrogen Production and Polymerization using Triarylboron‐Functionalized Iridium(III) Complexes

Abstract

The development of novel iridium(III) complexes has continued as an important area of research owing to their highly tunable photophysical properties and versatile applications. In this report, three heteroleptic dimesitylboron-containing iridium(III) complexes, [Ir(p-B-ppy) (N^N)] {p-B-ppy=2-(4-dimesitylborylphenyl)pyridine; N^N=dipyrido[3,2-a:2',3'-c]phenazine (dppz) (1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq) (2), and 1,10-phenanthroline (phen) (3)}, were prepared and fully characterized electrochemically, photophysically, and computationally. Altering the conjugated length of the N^N ligands allowed us to tailor the photophysical properties of these complexes, especially their luminescence wavelength, which could be adjusted from λ=583 to 631 nm in CH Cl . All three complexes were evaluated as visible-light-absorbing sensitizers for the photogeneration of hydrogen from water and as photocatalysts for the photopolymerization of methyl methacrylate. The results showed that all of them were active in both photochemical reactions. High activity for the photosensitizer (over 1158 turnover numbers with 1) was observed, and the system generated hydrogen even after 20 h. Additionally, poly(methyl methacrylate) with a relatively narrow molecular-weight distribution was obtained if an initiator (i.e., ethyl α-bromophenylacetate) was used. The living character of the photoinduced polymerization was confirmed on the basis of successful chain-extension experiments.

Recent Advances on Quinoxaline-Based Photoinitiators of Polymerization

“…Triphenylamine-modified quinoxalines were notably reported as exhibiting a two-photon value higher than 160 GM in the 780-820 nm range, greatly higher than the values reported for most of the benzil derivatives investigated as photoinitiators for two-photon initiated polymerization. Recently, a dipyrido[3,2-d:2 ,3 -f]quinoxaline (dpq) ligand was also used for the design of an iridium catalyst used for both the photogeneration of hydrogen from water and as a photocatalyst for the polymerization of methyl methacrylate [215]. However, the drawback of this approach is the toxicity of iridium and the scarcity of this metal on Earth.…”

Iron–N-heterocyclic carbene complexes as efficient electrocatalysts for water oxidation under acidic conditions

“…25,26 The combination of NHC and an electron-deficient boron atom (with an empty p orbital) results in special physical properties. 27 To the best of our knowledge, the first and only report about an iron-NHC complex in water oxidation was presented by Mazzoni and coworkers, who used a low-valent electrocatalyst, a cyclopentadienone-NHC iron(0) complex, under basic conditions. 28 However, they did not verify the performance under neutral or acidic conditions in the experiment.…”

Long-Lived Triplet Excited-State Bichromophoric Iridium Photocatalysts for Controlled Photo-Mediated Atom-Transfer Radical Polymerization

“…To our knowledge, only few iridium PCs, including fac -[Ir­(ppy) 3 ], ,,− Ir­(btp) 2 (tmd), and [Ir­( p -B-ppy) 2 (N^N)] + , have been applied in photo-mediated ATRP. The impact of reaction conditions on photo-mediated polymerization was investigated .…”