Crystalline ZnO photocatalysts with different morphologies prepared at ambient temperature

peer reviewe

Sulfonylation enabled through the photoactivation of EDA complexes

In this issue of Chem Catalysis, Molander and co-workers report the visible-light photoactivation of electron donor-acceptor (EDA) complexes formed between thianthrenium and sodium sulfinate derivatives to generate sulfone-containing compounds in moderate to good yields. This approach can be used for late-stage functionalization and enables the retention of halide handles

Chloride, Bromide, and Iodide Photooxidation in Acetonitrile/Water Mixtures Using Binuclear Iridium(III) Photosensitizers

Two iridium(III) binuclear photosensitizers, [Ir(dFCF3ppy)2(N–N)Ir(dFCF3ppy)2]2+, where N–N is tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine (Ir-TPPHZ) and 1,4,5,8-tetraazaphenanthrene[9,10-b]-1,4,5,8,9,12-hexaazatriphenylene (Ir-TAPHAT) are reported for iodide, bromide, and chloride photooxidation in acetonitrile and acetonitrile/water mixtures using blue-light irradiation. Excited-state reduction potentials Ered* of +2.02 and +2.09 V vs NHE were determined for Ir-TPPHZ and Ir-TAPHAT, respectively. Both photosensitizers’ excited states were efficiently quenched by iodide, bromide, and chloride with quenching rate constants in the (3.5–9.2) × 1010 and (0.0036–2.9) × 1010 M–1 s–1 ranges in neat acetonitrile and acetonitrile/water mixtures, respectively. Nanosecond transient absorption spectroscopy provided unambiguous evidence of reductive excited-state electron transfer, with all halides in the solvent mixtures containing up to 50% water. Cage-escape yields were large (55–96%) in acetonitrile and dropped below 32% in 50:50 acetonitrile/water mixtures

Synthesis of Ru(II) and Os(II) Photosensitizers Bearing one 9,10-diamino-1,4,5,8-tetraazaphenanthrene Scaffold

The synthesis of eight novel Ru(II) and Os(II) photosensitizers bearing a common 9,10-disubstituted-1,4,5,8-tetraazaphenanthrene backbone is reported. With Os(II) photosensitizers, the 9,10-diNH2-1,4,5,8-tetraazaphenanthrene could be directly chelated onto the metal center via the heteroaromatic moiety, whereas similar conditions using Ru(II) resulted in the formation of an o-quinonediimine derivative. Hence, an alternative route, proceeding via the chelation of 9-NH2-10-NO2-1,4,5,8-tetraazaphenanthrene and subsequent ligand reduction of the corresponding photosensitizers was developed. Photosensitizers chelated via the polypyridyl-type moiety exhibited classical photophysical properties whereas the o-quinonediimine chelated Ru(II) analogues exhibited red-shifted absorption (520 nm) and no photoluminescence at room temperature in acetonitrile. The most promising photosensitizers were investigated for excited-state quenching with guanosine-5’-monophosphate in aqueous buffered conditions where reductive excited-state electron transfer was observed by nanosecond transient absorption spectroscopy

A protocol for determining cage-escape yields using nanosecond transient absorption spectroscopy

Here, we present a protocol for the determination of cage-escape yields following excited-state electron transfer between a photosensitizer and a quencher. We describe steps for determining changes in molar absorption coefficient of the different oxidation states via photolysis experiments and the percentage of reacted species via steady-state or time-resolved spectroscopy. We then detail measurement of the amount of formed product via nanosecond transient absorption spectroscopy

Spectroscopic Techniques to Unravel Mechanistic Details in Light‐Induced Transformations and Photoredox Catalysis

The rapid development of photo(redox) catalysis within the last decades is remarkable to the extent that the utilization of light-driven processes in organic chemistry has become a credible alternative to current thermal processes. Such advances offer tremendous opportunities of collaborations between scientific realms that can have a drastic impact on the development of the field. In this concept article, a special emphasis is placed on spectroscopic techniques that are used, or could be used, for light-induced transformations and photoredox catalysis applications. These include spectroelectrochemistry, UV-VIS, IR and X-Ray transient absorption spectroscopy, laser pulsed radiolysis (PR), photo-induced chemically induced dynamic nuclear polarization (Photo-CIDNP), photoacoustic spectroscopy, time-resolved Raman spectroscopy (TRRS), time-resolved Electron Paramagnetic Resonance (TREPR) and time-resolved dielectric loss spectroscopy (TRDL). The theoretical background behind each technique is briefly introduced followed by selected relevant examples from the literature

Accumulation of mono-reduced [Ir(piq)2(LL)] photosensitizers relevant for solar fuels production

A series of nine [Ir(piq)2(LL)]+.PF6– photosensitizers, where piqH = 1-phenylisoquinoline, was developed and investigated for excited-state electron transfer with sacrificial electron donors that included triethanolamine (TEOA), triethylamine (TEA) and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) in acetonitrile. The photosensitizers were obtained in 57–82% yield starting from the common [Ir(piq)2µ-Cl]2 precursor and were all characterized by UV–Vis absorption as well as by steady-state, time-resolved spectroscopies and electrochemistry. The excited-state lifetimes ranged from 250 to 3350 ns and excited-state electron transfer quenching rate constants in the 109 M–1 s–1 range were obtained when BIH was used as electron donor. These quenching rate constants were three orders of magnitude higher than when TEA or TEOA was used. Steady-state photolysis in the presence of BIH showed that the stable and reversible accumulation of mono-reduced photosensitizers was possible, highlighting the potential use of these Ir-based photosensitizers in photocatalytic reactions relevant for solar fuels production

Phendione-Transition Metal Complexes with Bipolar Redox for Lithium Batteries

1,10-Phenanthroline-5,6-dione (Phendione) - based transition metal complexes are known for their use in pharmacological and catalysis applications. However, their application in electrochemical energy storage has not been investigated thus far. Herein we prove the feasibility of employing phendione - transition metal complexes for electrochemical charge storage by taking advantage of the reversible redox of both, carbonyl groups and transition metal center, contributing thus to augmented charge storage. Interestingly, the chemistry of the counter ion in the studied complexes effectively tunes the solubility and improves the cycling stability. Whereas further studies are required to limit the solubility and active species shuttle, this study explores the bottlenecks of phendione - transition metal complexes as electrode materials for solid electrode format batteries. </i

Phendione‐Transition Metal Complexes with Bipolar Redox for Lithium Batteries

1,10‐Phenanthroline‐5,6‐dione (Phendione) ‐ based transition metal complexes are known for their use in pharmacological and catalysis applications. However, their application in electrochemical energy storage has not been investigated thus far. Herein we prove the feasibility of employing phendione ‐ transition metal complexes for electrochemical charge storage by taking advantage of the reversible redox of both, carbonyl groups and transition metal center, contributing thus to augmented charge storage. Interestingly, the chemistry of the counter ion in the studied complexes effectively tunes the solubility and improves the cycling stability. Whereas further studies are required to limit the solubility and active species shuttle, this study explores the bottlenecks of phendione ‐ transition metal complexes as electrode materials for solid electrode format batteries

Chloride, Bromide, and Iodide Photooxidation in Acetonitrile/Water Mixtures Using Binuclear Iridium(III) Photosensitizers

Two iridium(III) binuclear photosensitizers, [Ir(dFCF3ppy)2(N–N)Ir(dFCF3ppy)2]2+, where N–N is tetrapyrido[3,2-a:2′,3′-c:3″,2″-h:2‴,3‴-j]phenazine (Ir-TPPHZ) and 1,4,5,8-tetraazaphenanthrene[9,10-b]-1,4,5,8,9,12-hexaazatriphenylene (Ir-TAPHAT) are reported for iodide, bromide, and chloride photooxidation in acetonitrile and acetonitrile/water mixtures using blue-light irradiation. Excited-state reduction potentials Ered* of +2.02 and +2.09 V vs NHE were determined for Ir-TPPHZ and Ir-TAPHAT, respectively. Both photosensitizers’ excited states were efficiently quenched by iodide, bromide, and chloride with quenching rate constants in the (3.5–9.2) × 1010 and (0.0036–2.9) × 1010 M–1 s–1 ranges in neat acetonitrile and acetonitrile/water mixtures, respectively. Nanosecond transient absorption spectroscopy provided unambiguous evidence of reductive excited-state electron transfer, with all halides in the solvent mixtures containing up to 50% water. Cage-escape yields were large (55–96%) in acetonitrile and dropped below 32% in 50:50 acetonitrile/water mixtures