Sn(IV) Metalloporphyrin/Co(III) Complex: An All-Abundant-Element System for the Photocatalytic Production of H2 in Aqueous Solution

Defective Potassium Poly(Heptazine Imide) Preventing Spin Delocalization and Hole Transfer Deactivation for Efficient Solar Energy Conversion and Storage

Anti-site defective potassium poly(heptazine imide) (KPHI) with the central nitrogen atoms partially replaced by graphitic carbon atoms in the flawed heptazine rings is prepared by direct ionothermal treatment of the rationally designed supramolecular complex in KSCN salt molten. Compared to the KPHIs without the anti-site defect, the anti-site defective KPHI demonstrates significantly improved photocatalytic and dark photocatalytic performances for H2 evolution reaction (HER). In the presence of the hole scavenger, the anti-site defective KPHI exhibits superior photocatalytic stability for HER lasting 20 h, whereas the deactivation is observed from the ordinary KHPIs after 3 h HER. Moreover, the H2 yield in the dark by the stored photoelectrons in the anti-site defective KPHI increases by more than an order of magnitude. Density functional theory calculations reveal that the anti-site defective unit in KPHI not only prevents spin delocalization but also inhibits the deactivation of hole transfer, which are beneficial to photoelectron storage and photocatalytic activity. The findings in this study provide insight into the photophysical and catalytic properties of KPHI, which conclude a strategy to improve the performances for solar energy conversion and storage by incorporating intrinsic anti-site defects in KPHI.

Porphyrins and phthalocyanines as biomimetic tools for photocatalytic H2 production and CO2 reduction

The increasing energy demand and environmental issues caused by the over-exploitation of fossil fuels render the need for renewable, clean, and environmentally benign energy sources unquestionably urgent. The zero-emission energy carrier, H₂ is an ideal alternative to carbon-based fuels especially when it is generated photocatalytically from water. Additionally, the photocatalytic conversion of CO₂ into chemical fuels can reduce the CO₂ emissions and have a positive environmental and economic impact. Inspired by natural photosynthesis, plenty of artificial photocatalytic schemes based on porphyrinoids have been investigated. This review covers the recent advances in photocatalytic H₂ production and CO₂ reduction systems containing porphyrin or phthalocyanine derivatives. The unique properties of porphyrinoids enable their utilization both as chromophores and as catalysts. The homogeneous photocatalytic systems are initially described, presenting the various approaches for the improvement of photosensitizing activity and the enhancement of catalytic performance at the molecular level. On the other hand, for the development of the heterogeneous systems, numerous methods were employed such as self-assembled supramolecular porphyrinoid nanostructures, construction of organic frameworks, combination with 2D materials and adsorption onto semiconductors. The dye sensitization on semiconductors opened the way for molecular-based dye-sensitized photoelectrochemical cells (DSPECs) devices based on porphyrins and phthalocyanines. The research in photocatalytic systems as discussed herein remains challenging since there are still many limitations making them unfeasible to be used at a large scale application before finding a large-scale application.

The odyssey of cobaloximes for catalytic H2 production and their recent revival with enzyme-inspired design

Cobaloxime complexes gained attention for their intrinsic ability of catalytic H₂ production despite their initial emergence as a vitamin B12 model. The simple, robust, and synthetically manoeuvrable cobaloxime core represents a model catalyst molecule for the investigation of optimal conditions for both photo- and electrocatalytic H₂ production catalytic assemblies. Cobaloxime is one of the rare catalysts that finds equal applications in the analysis of homogeneous and heterogeneous catalytic conditions. However, the poor aqueous solubility and long-term instability of cobaloximes have severely impeded their growth. Lately, interest in the cobaloxime-based catalysts has been resuscitated with the rational use of extended enzymatic features. This unique enzyme-inspired catalyst design strategy has instigated the formation of a new genre of cobaloxime molecules that exhibit enhanced photo- and electrocatalytic H₂ evolution with improved aqueous and air stability.

Enhancing photocatalytic hydrogen evolution by intramolecular energy transfer in naphthalimide conjugated porphyrins

Three new isomeric naphthalimide conjugated porphyrins are developed for photocatalytic H₂ production. The para-substituted isomer, ZnT(p-NI)PP delivers the highest rate (ηH₂) of 973 μmol g⁻¹ h⁻¹ due to the efficient intramolecular energy transfer from the naphthalimide to the porphyrin core.

Structure-Activity and Stability Relationships for Cobalt Polypyridyl-Based Hydrogen-Evolving Catalysts in Water

A series of eight new and three known cobalt polypyridyl-based hydrogen-evolving catalysts (HECs) with distinct electronic and structural differences are benchmarked in photocatalytic runs in water. Methylene-bridged bis-bipyridyl is the preferred scaffold, both in terms of stability and rate. For a cobalt complex of the tetradentate methanol-bridged bispyridyl-bipyridyl complex [Co^II Br(tpy)]Br, a detailed mechanistic picture is obtained by combining electrochemistry, spectroscopy, and photocatalysis. In the acidic branch, a proton-coupled electron transfer, assigned to formation of Co^III -H, is found upon reduction of Co^II , in line with a pK_a (Co^III -H) of approximately 7.25. Subsequent reduction (-0.94 V vs. NHE) and protonation close the catalytic cycle. Methoxy substitution on the bipyridyl scaffold results in the expected cathodic shift of the reduction, but fails to change the pK_a (Co^III -H). An analysis of the outcome of the benchmarking in view of this postulated mechanism is given along with an outlook for design criteria for new generations of catalysts.

Evidence for photosensitised hydrogen production from water in the absence of precious metals, redox-mediators and co-catalysts

New approaches for sunlight-powered proton reduction and photocatalytic hydrogen evolution from aqueous salt solutions using earth-abundant components and molecular photosensitisers.

Photochemical hydrogen evolution using Sn-porphyrin as photosensitizer and a series of Cobaloximes as catalysts

Herein, we report a photochemical hydrogen evolution system consisting of various cobalt based catalysts, a metallated Sn porphyrin as photosensitizer and a triethanolamine as a sacrificial electron donor in acetonitrile/H2O (1:1) solution. Since a tin metallated porphyrin is used for the first time as photosensitizer in this type of systems, a systematic study was performed in order to elucidate the best conditions for H[Formula: see text]production. Upon visible irradiation hydrogen production was detected with the best result obtained at pH 7 with a TON of 150, after 100 h in the presence of catalyst 1. Moreover, when TiO2 nanoparticles were added at the catalytic system 2 the hydrogen production was increased from 53 TON to 131 TON, under the same experimental conditions.

V. Synthesis of new fused heterocyclic aromatic hydrocarbons via C–S and C–C bond formation by C–H bond activation in the presence of new Pd(ii) Schiff's base complexes

Pd(ii) Schiff base macrocyclic complexes are used as photocatalysts with high stability, C–S bond and intramolecular C–H bond activation under visible light irradiation.