Elaboration of Covalently Linked Polyoxometalates with Ruthenium and Pyrene Chromophores and Characteriation of Their Photophysical Properties

Abstract

Keggin and Dawson-type polyoxometalates (POMs) decorated by organometallic [cyclometalated ruthenium(II) polypyridine complex] or organic (pyrene) chromophores were prepared by postfunctionalization of hybrid disilylated POM platforms. The connection is made in a very efficient and modular way via Sonogashira coupling reactions, which provide a rigid linkage between the POM and the photoactive centers. Electronic properties have been inferred from electrochemical and photophysical studies and reflect poor electronic interactions between both partners. The presence of the POM leads to luminescence quenching of the chromophores, which was attributed to an intramolecular electron transfer from the chromophore to the POM. The rate of this process is much faster in the POM-pyrene than in the POM-Ru system. It depends on the driving force dictated by the redox potentials of both partners but also in the case of the POM-Ru system on the presence of the metallacycle, which acts as a molecular insulator and delays the intramolecular electron transfer. In the POM-Ru system, a comparative study of the luminescence quenching showed that the electron transfer is still more important in the covalently bonded hybrids than in systems where the POM and the ruthenium complexes are assembled via electrostatic interactions.

Naphthyl-Containing Organophosphonate Derivatives of Keggin-Type Polyoxotungstates

“…400 nm that could be ascribed to a charge transfer between the aromatic system and the inorganic POM cluster in which the former acts as electron donor and the latter as acceptor. This phenomenon has been previously observed for similar compounds in the literature [61,62]. The charge-transfer process can be noticed visually because the incorporation of the colorless 1-naphthylmethylphosphonate moiety into the inorganic skeleton of the colorless {SiW 11 } leads to the formation of the orange-yellow compound TBA-2.…”

“…TD-DFT calculations support the latter interpretation as they clearly show that the naphthyl groups in the hybrid POMs 1 and 2 are excited in the 280-290 nm range ( Figure 6D,E). Analogous quenching of the photoluminescent properties of aromatic systems such as pyrene upon incorporation into POM cluster frameworks has been previously reported in the literature for hybrid species similar to polyanions 1 and 2 [62]. …”

Charge photo-accumulation and photocatalytic hydrogen evolution under visible light at an iridium(iii)-photosensitized polyoxotungstate

“…Indeed, in classical donor-acceptor (D-A) systems, the electron acceptor, once reduced, potentially becomes an electron donor and often displays lightabsorbing properties. Thus it may act, in a subsequent light-driven process, as a deleterious 47,48 In the previously mentioned study, transient absorptions measurements only allowed for the characterization of the first photo-induced electron transfer. Charge photo-accumulation studies can be achieved in the presence of an additional electron donor in the solution that can irreversibly quench the charge separation state, regenerate the initial state of the photosensitizer and make a second photo-induced process possible.…”

“…The kinetics of charge separation and charge recombination in these reported POM-[Ir] hybrids were correlated to the redox potential of the POM with the fastest electron transfer rates (both charge separation and charge recombination) observed for the POMs that are the most easily reduced. 47,48 In the previously mentioned study, transient absorptions measurements only allowed for the characterization of the first photo-induced electron transfer. Charge photo-accumulation studies can be achieved in the presence of an additional electron donor in the solution that can irreversibly quench the charge separation state, regenerate the initial state of the photosensitizer and make a second photo-induced process possible.…”

Simulating the Favorable Aggregation of Monolacunary Keggin Anions

“…12,13 In addition, the rectangular lacuna in MKAs represents an ideal binding site wherein to anchor a variety of functional moieties and/or linkers: [14][15][16][17] in practice, this somewhat broadens MKAs' versatility with respect to that of PKAs. Notable examples are organic tethers to chromophores; 12,18,19 to (photo)catalytic centres; 13,[20][21][22] to other solid supports such as electrodes, silica, and metal oxides; 9,19,[23][24][25][26] and to distal metal chelating centres, for subsequent incorporation in co-ordination polymers. 26,27 Just as significant as these intrinsic chemical properties is the dynamic behaviour of Keggin anions in solution.…”