Noble Metal-Free Light-Driven Hydrogen Evolution Catalysis in Polyampholytic Hydrogel Networks.

Future technologies to harness solar energy and to convert this into chemical energy strongly rely on straightforward approaches to prepare versatile soft matter scaffolds for the immobilization of catalysts and sensitizers in a defined environment. In addition, particularly for light-driven hydrogen evolution, a transition to noble metal-free photosensitizers and catalysts is urgently required. Herein, we report a fully organic light-harvesting soft matter network based on a polyampholyte hydrogel where both photosensitizer (a perylene monoimide derivative) and a H2 evolution catalyst ([Mo3S13]2-) are electrostatically incorporated. The resulting material exhibits sustained visible-light-driven H2 evolution in aqueous ascorbic acid solution, even at rather low loadings of photosensitizer (0.4%) and catalyst (120 ppm). In addition, we provide initial insights into the long-term stability of the hybrid hydrogel. We believe that these results pave the way for a generalized route toward the incorporation of noble metal-free light-driven catalysis in soft matter networks.

Optimizing reaction conditions for the light-driven hydrogen evolution in a loop photoreactor.

Photocatalytic hydrogen production from water is a promising way to fulfill energy demands and attain carbon emission reduction goals effectively. In this study, a loop photoreactor with a total volume of around 500 mL is presented for the photocatalytic hydrogen evolution using a Pt-loaded polymeric carbon nitride photocatalyst under 365 nm irradiation in the presence of sacrificial reducing agents. The fluid flow pattern of the developed photoreactor was characterized experimentally and the photon flux incident to the loop photoreactor was measured by chemical actinometry. The system displayed exceptional stability, with operation sustained over 70 hours. A design of experiment (DOE) analysis was used to systematically investigate the influence of key parameters - photon flux, photocatalyst loading, stirring speed, and inert gas flow rate - on the hydrogen generation rate. Linear relationships were found between hydrogen evolution rate and photon flux as well as inert gas flow rate. Photocatalyst loading and stirring speed also showed linear correlations, but could not be correctly described by DOE analysis. Instead, linear single parameter correlations could be applied. Notably, the loop photoreactor demonstrated an external photon efficiency up to 17 times higher than reported in literature studies, while scaling the reactor size by a factor of 10.

Methylation of Unactivated Alkenes with Engineered Methyltransferases To Generate Non-natural Terpenoids.

Terpenoids are built from isoprene building blocks and have numerous biological functions. Selective late-stage modification of their carbon scaffold has the potential to optimize or transform their biological activities. However, the synthesis of terpenoids with a non-natural carbon scaffold is often a challenging endeavor because of the complexity of these molecules. Herein we report the identification and engineering of (S)-adenosyl-l-methionine-dependent sterol methyltransferases for selective C-methylation of linear terpenoids. The engineered enzyme catalyzes selective methylation of unactivated alkenes in mono-, sesqui- and diterpenoids to produce C11 , C16 and C21 derivatives. Preparative conversion and product isolation reveals that this biocatalyst performs C-C bond formation with high chemo- and regioselectivity. The alkene methylation most likely proceeds via a carbocation intermediate and regioselective deprotonation. This method opens new avenues for modifying the carbon scaffold of alkenes in general and terpenoids in particular.

Boosting Efficiency in Light-Driven Water Splitting by Dynamic Irradiation through Synchronizing Reaction and Transport Processes.

This work elaborates the effect of dynamic irradiation on light-driven molecular water oxidation to counteract deactivation. It highlights the importance of overall reaction engineering to overcome limiting factors in artificial photosynthesis reactions. Systematic investigation of a homogeneous three-component ruthenium-based water oxidation system revealed significant potential to enhance the overall catalytic efficiency by synchronizing the timescales of photoreaction and mass transport in a capillary flow reactor. The overall activity could be improved by a factor of more than 10 with respect to the turnover number and a factor of 31 referring to the external energy efficiency by controlling the local availability of photons. Detailed insights into the mechanism of light driven water oxidation could be obtained using complementary methods of investigation like Raman, IR, and UV/Vis/emission spectroscopy, unraveling the importance of avoiding high concentrations of excited photosensitizers.

Activating a [FeFe] Hydrogenase Mimic for Hydrogen Evolution under Visible Light.

Inspired by the active center of the natural [FeFe] hydrogenases, we designed a compact and precious metal-free photosensitizer-catalyst dyad (PS-CAT) for photocatalytic hydrogen evolution under visible light irradiation. PS-CAT represents a prototype dyad comprising π-conjugated oligothiophenes as light absorbers. PS-CAT and its interaction with the sacrificial donor 1,3-dimethyl-2-phenylbenzimidazoline were studied by steady-state and time-resolved spectroscopy coupled with electrochemical techniques and visible light-driven photocatalytic investigations. Operando EPR spectroscopy revealed the formation of an active [FeI Fe0 ] species-in accordance with theoretical calculations-presumably driving photocatalysis effectively (TON≈210).

1,7,9,10-Tetrasubstituted PMIs Accessible through Decarboxylative Bromination: Synthesis, Characterization, Photophysical Studies, and Hydrogen Evolution Catalysis.

In this work, we present a new synthetic strategy for fourfold-substituted perylene monoimides via tetrabrominated perylene monoanhydrides. X-ray diffraction analysis unveiled the intramolecular stacking orientation between the substituents and semicircular packing behavior. We observed the remarkable influence of the substituent on the longevity and nature of the excited state upon visible light excitation. In the presence of poly(dehydroalanine)-graft-poly(ethylene glycol) graft copolymers as solubilizing template, the chromophores are capable of sensitizing [Mo3 S13 ]2- clusters in aqueous solution for stable visible light driven hydrogen evolution over three days.