Structure and isomerization behavior relationships of new push-pull azo-pyrrole photoswitches

A family of stilbenyl-azopyrroles compounds 2a-d and 3a-d was efficiently obtained via a Mizoroki-Heck C-C-type coupling reaction between 2-(4'-iodophenyl-azo)-N-methyl pyrrole (1a) and different vinyl precursors. The influence of the π-conjugated backbone and the effect of the pyrrole moiety were correlated with their optical properties. Studies via UV-Visible spectrophotometry revealed that the inclusion of EWG or EDG favors a red-shift of the main absorption band in these azo compounds compared with their non-substituted analogues. Furthermore, there is a clear influence between the half-life of the Z isomer formed by irradiation with white light and the push-pull behavior of the molecules. In several cases, the stilbenyl-azopyrroles led to the formation of J-type aggregates in binary MeOH : H2O solvents, which are of interest for water compatible applications.

Synthesis of Photochromic Phosphines by Pd-Catalyzed Annulation Reaction of Alkynes Bearing Phosphinyl Substituent with a Silacyclopropene

The synthesis of phosphines with light controlled basicity is presented in this study. A methodological approach for the preparation of these unconventional photochromic phosphines based on a dithienylethene organic moiety is reported. It relies on the palladium-catalyzed annulation of alkynyl phosphines in the presence of a 2,3-Dithienylsilacyclopropene. Accordingly, a diphenyphosphino moiety is connected to the organic photochrome thanks to different linkers. Their influence on the photochromism and on the phosphinyl group basicity is studied and evaluated based on experimental an NMR descriptor as well as DFT calculations.

Enhanced stability of sub-nanometric iridium decorated graphitic carbon nitride for H2 production upon hydrous hydrazine decomposition

Stabilizing metal nanoparticles is vital for large scale implementations of supported metal catalysts, particularly for a sustainable transition to clean energy, e.g., H₂ production. In this work, iridium sub-nanometric particles were deposited on commercial graphite and on graphitic carbon nitride by a wet impregnation method to investigate the metal-support interaction during the hydrous hydrazine decomposition reaction. To establish a structure-activity relationship, samples were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The catalytic performance of the synthesized materials was evaluated under mild reaction conditions, i.e. 323 K and ambient pressure. The results showed that graphitic carbon nitride (GCN) enhances the stability of Ir nanoparticles compared to graphite, while maintaining remarkable activity and selectivity. Simulation techniques including Genetic Algorithm geometry screening and electronic structure analyses were employed to provide a valuable atomic level understanding of the metal-support interactions. N anchoring sites of GCN were found to minimise the thermodynamic driving force of coalescence, thus improving the catalyst stability, as well as to lead charge redistributions in the cluster improving the resistance to poisoning by decomposition intermediates.

Formation of Irida-β-ketoimines and PCNamine-Ir(III) Complexes by Reacting Irida-β-diketones with Aliphatic Diamines: Catalytic Activity in Hydrogen Release by Methanolysis of H3N-BH3

Aliphatic diamines [(H2N(CH2)nNHR) (a-d) n = 2: R = H (a), R = CH3 (b), R = C2H5 (c), n = 3, R = H (d) or rac-2-(aminomethyl)piperidine (e)] react with [IrH(Cl){(PPh2(o-C6H4CO))2H}] in THF to afford ketoimine complexes [IrH(Cl){(PPh2(o-C6H4CO))(PPh2(o-C6H4CN(CH2)nNHR))H}] (2a-2d) or [IrH(Cl){(PPh2(o-C6H4CO))(PPh2(o-C6H4CNCH2(C5H9NH)))H}] (2e), containing a bridging N-H···O hydrogen bond and a dangling amine. Complex 2e consists of an almost equimolar mixture of two diastereomers. In protic solvents, the dangling amine in complexes 2 displaces chloride to afford cationic acyl-iminium compounds, [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4CNH(CH2)nNHR))]X (3a-3d, X = Cl) or [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4CNHCH2(C5H9NH)))]Cl (3e) and (4a-4b, X = ClO4), with new hemilabile terdentate PCNamine ligands adopting a facial disposition. Complexes 3 contain the corresponding phosphorus atom trans to hydride and the amine fragment trans to acyl, while complexes 4 contain the amine trans to hydride. 3b and 4b consist of 80:20 and 95:5 mixtures of diastereomers, respectively, while 3e contains a 65:35 mixture. In the presence of KOH, intermediate cationic acyl-iminium complexes 3 transform into neutral acyl-imine [IrH(PPh2(o-C6H4CO))(PPh2(o-C6H4CN(CH2)nNHR))] derivatives (5) with retention of the stereochemistry. Single-crystal X-ray diffraction analysis was performed on 2a, [3a]Cl, [3b]Cl, [4a]ClO4, and 5b. Complexes 2, 3, and 5 catalyze the methanolysis of ammonia-borane under air to release hydrogen. The highest activity is observed for ketoimine complexes 2.

Multiple Azoarenes Based Systems - Photoswitching, Supramolecular Chemistry and Application Prospects

In the recent decades, the investigations on photoresponsive molecular systems with multiple azoarenes are quite popular in diverse perspectives ranging from fundamental understanding of multiple photoswitches, supramolecular chemistry, and various application prospects. In fact, several insightful and conceptual designs of such systems were investigated with architectural distinctions. In particular, the demonstration of applications such as data storage with the help of multistate or orthogonal photoswitches, light modulation of catalysis via cooperative switching, sensors using supramolecular host-guest interactions, and materials such as liquid crystals, grating, actuators, etc. are some of the milestones in this area. Herein, we cover the recent advancements in the research areas of multiazoarenes containing systems that have been classified into Type-1 {linear, non-linear, and core-based (A)}, Type-2 {tripodal C₃ -symmetric (C3)} and Type-3 {macrocyclic (M)} structural motifs.

Advances in the Structural Strategies of the Self-Assembly of Photoresponsive Supramolecular Systems

Photosensitive supramolecular systems have garnered attention due to their potential to catalyze highly specific tasks through structural changes triggered by a light stimulus. The tunability of their chemical structure and charge transfer properties provides opportunities for designing and developing smart materials for multidisciplinary applications. This review focuses on the approaches reported in the literature for tailoring properties of the photosensitive supramolecular systems, including MOFs, MOPs, and HOFs. We discuss relevant aspects regarding their chemical structure, action mechanisms, design principles, applications, and future perspectives.

Solid-state photochromic arylazopyrazole based transition metal complexes

A new class of photoactive and chelating ligands L1-3 have been designed and synthesized by incorporating arylazo-3,5-dimethylpyrazole units in the ligand frameworks. Significantly they are designed in such a way...

Metal complexes bearing photochromic ligands: photocontrol of functions and processes

Metal complexes associated with photochromic molecules are attractive platforms to achieve smart light-switching materials with innovative and exciting properties due to specific optical, electronic, magnetic or catalytic features of metal complexes and by perturbing the excited-state properties of both components to generate new reactivity and photochemical properties. In this overview, we focus on selected achievements in key domains dealing with optical, redox, magnetic properties, as well as application in catalysis or supramolecular chemistry. We also try to point out scientific challenges that are still faced for future developments and applications.

Azopyridine-based chiral oxazolines with rare-earth metals for photoswitchable catalysis

An azopyridine-based oxazoline was developed for utilizing azo group coordination and isomerization as a photoswitchable ligand. The ligand coordinated to rare-earth metal (RE) catalyst underwent efficient E/Z photoisomerization, suggesting tri- and bidentate coordination switching. The photoisomerization of the ligand enabled modulation of the enantioselectivity of an RE-catalyzed aminal forming reaction.

Reduction of Carbon Dioxide with Ammonia-Borane under Ambient Conditions: Maneuvering a Catalytic Way

In the development of alternatives to the traditional catalytic hydrogenation of CO₂ with gaseous H₂, employing nongaseous H₂ storage compounds as potential reductants for catalytic transfer hydrogenation of CO₂ is promising. Ammonia-borane, due to its high hydrogen storage capacity (19.6 wt %), has been used for catalytic transfer hydrogenation of several organic unsaturated compounds. However, a similar protocol involving catalytic transfer hydrogenation of less reactive CO₂ with NH₃BH₃ is yet to be realized experimentally. Herein, we demonstrate the first catalytic CO₂ transfer hydrogenation process for generating formate salt with NH₃BH₃ under ambient conditions (1 atm and 30 °C) employing a cationic "Ir(III)-abnormal NHC" catalyst via an electrophilic NH₃BH₃ activation route. It exhibited an initial turnover frequency of 686 h^-1 and a high turnover number (TON) of ≈1300 in just 4 h. Most significantly, the catalyst was durable enough to maintain long-term activity, and upon only periodic recharging of NH₃BH₃, it furnished a total TON of >4200 in 10 h.

Photoswitchable catalysis using organometallic complexes

Photoswitchable catalysis using organometallic complexes: a ligand design perspective.

Photoswitchable catalysis based on the isomerisation of double bonds

Photoswitchable catalysis is a young but rapidly evolving field that offers great potential for non-invasive dynamic control of both activity and selectivity in catalysis. This Feature Article summarises the key developments accomplished over the past years through the incorporation of photoswitchable double bonds into the structure of catalytically competent molecules.