Quaterpyridine Ligands for Panchromatic Ru(II) Dye Sensitizers

A new general synthetic access to carboxylated quaterpyridines (qpy), of interest as ligands for panchromatic dyesensitized solar cell organometallic sensitizers, is presented. The strategic step is a Suzuki−Miyaura cross-coupling reaction, which has allowed the preparation of a number of representative unsubstituted and alkyl and (hetero)aromatic substituted qpys. To bypass the poor inherent stability of 2-pyridylboronic acid derivatives, we successfully applied N-methyliminodiacetic acid (MIDA) boronates as key reagents, obtaining the qpy ligands in good yields up to (quasi)gram quantities. The structural, spectroscopic (NMR and UV−vis), electrochemical, and electronic characteristics of the qpy have been experimentally and computationally (DFT) investigated. The easy access to the bis-thiocyanato Ru(II) complex of the parent species of the qpy series, through an efficient route which bypasses the use of Sephadex column chromatography, is shown. The bis-thiocyanato Ru(II) complex has been spectroscopically (NMR and UV−vis), electrochemically, and computationally investigated, relating its properties to those of previously reported Ru(II)−qpy complexes.“This document is the Accepted Manuscript version of a Published Work that appeared in final form in [The Journal of Organic Chemistry], copyright © American Chemical Society after peer review and technical editing by the publisher

Design of Ru(II) sensitizers endowed by three anchoring units for adsorption mode and light harvesting optimization

We report the design, synthesis and computational investigation of a class of Ru(II)-dyes based on mixed bipyridine ligands for use in dye-sensitized solar cells. These dyes are designed to preserve the optimal anchoring mode of the prototypical N719 sensitizer by three carboxylic groups, yet allowing for tunable optimization of their electronic and optical properties by selective substitution at one of the 4-4′ positions of a single bipyridine ligand with π-excessive heteroaromatic groups. We used Density Functional Theory/Time Dependent Density Functional Theory calculations to analyze the electronic structure and optical properties of the dye and to investigate the dye adsorption mode on a TiO2 nanoparticle model. Our results show that we are effectively able to introduce three carboxylic anchoring units into the dye and achieve at the same time an enhanced dye light harvesting, demonstrating the design concept. As a drawback of this type of dyes, the synthesis leads to a mixture of dye isomers, which are rather tedious to separate

NUOVI COMPOSTI OTTICAMENTE SENSIBILI AI COMPOSTI ELETTRON­POVERI

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Molecular electro- and photocatalytic approach to artificial nitrogen fixation for the synthesis of green ammonia

Ammonia (NH3) stands as a cornerstone compound across industries, pivotal in agriculture, chemicals, and energy sectors. However, the conventional Haber-Bosch process demands high pressures, temperatures, and fossil fuels, calling for sustainable alternatives. Electrocatalytic Nitrogen Reduction Reactions (E-NRRs) and Photocatalytic Nitrogen Reduction Reactions (Photo-NRRs) present innovative routes, leveraging electricity and direct sunlight to convert nitrogen (N2) to NH3 under mild conditions, reducing emissions and softening energy requirements. Catalysts play a strategic role in these approaches, overcoming activation barriers and enhancing efficiency. However, some challenges still need to be addressed. Indeed, noble metals exhibit limits and their scarcity, geopolitical involvement, and often fluctuating costs inhibit large-scale use. Non-noble metals offer promise but require optimization and face durability concerns. Finally, carbon-based catalysts present challenges in optimization and doping. In this scenario, a molecular-based approach, comprising both specific single coordination-based molecules with transition metal centres and either metal centre coordination-based or fully organic multi-dimensional networks originating from direct molecular organic precursors, overcomes these issues while keeping the benefits of the previously mentioned classes of compounds. This mini-review explores the molecular approach to E-NRRs and Photo-NRRs from coordination compounds carrying porphyrins and phthalocyanines as organic ligands to polymeric networks based on coordination compounds between metallic centres and organic ligands (Metal-Organic Frameworks), and to networks of molecular organic units into multi-dimensional structures (Covalent Organic Frameworks). Mechanistic insights into E-NRRs and Photo-NRRs pathways elucidate N2 conversion to NH3. A critical comparative evaluation of reported catalysts has been carried out to highlight the limits and the possibilities of each class of compounds. Although challenges persist in terms of stability, cost and complexity of the synthesis, the use of a molecular approach in NRRs represents one of the most promising routes towards the sustainable preparation of ammonia

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