Borylation in the Second Coordination Sphere of Fe(II) Cyanido Complexes and Its Impact on Their Electronic Structures and Excited-State Dynamics

Second coordination sphere interactions of cyanido complexes with hydrogen-bonding solvents and Lewis acids are known to influence their electronic structures, whereby the non-labile attachment of B(C6F5)3 resulted in several particularly interesting new compounds lately. Here, we investigate the effects of borylation on the properties of two FeII cyanido complexes in a systematic manner by comparing five different compounds and using a range of experimental techniques. Electrochemical measurements indicate that borylation entails a stabilization of the FeII-based t2g-like orbitals by up to 1.65 eV, and this finding was confirmed by Mössbauer spectroscopy. This change in the electronic structure has a profound impact on the UV–vis absorption properties of the borylated complexes compared to the non-borylated ones, shifting their metal-to-ligand charge transfer (MLCT) absorption bands over a wide range. Ultrafast UV–vis transient absorption spectroscopy provides insight into how borylation affects the excited-state dynamics. The lowest metal-centered (MC) excited states become shorter-lived in the borylated complexes compared to their cyanido analogues by a factor of ∼10, possibly due to changes in outer-sphere reorganization energies associated with their decay to the electronic ground state as a result of B(C6F5)3 attachment at the cyanido N lone pair

Competing dynamics of intramolecular deactivation and bimolecular charge transfer processes in luminescent Fe( iii ) N-heterocyclic carbene complexes

Steady state and ultrafast spectroscopy on [Fe$^{III}$(phtmeimb)$_{2}$]PF$_{6}$ (phtmeimb = phenyl(tris(3-methylimidazol-2-ylidene))borate) was performed over a broad range of temperatures. The intramolecular deactivation dynamics of the luminescent doublet ligand-to-metal charge-transfer ($^{2}$LMCT) state was established based on Arrhenius analysis, indicating the direct deactivation of the $^{2}$LMCT state to the doublet ground state as a key limitation to the lifetime. In selected solvent environments photoinduced disproportionation generating short-lived Fe(IV) and Fe(II) complex pairs that subsequently undergo bimolecular recombination was observed. The forward charge separation process is found to be temperature-independent with a rate of ∼1 ps$^{–1}$. Subsequent charge recombination takes place in the inverted Marcus region with an effective barrier of 60 meV (483 cm$^{–1}$). Overall, the photoinduced intermolecular charge separation efficiently outcompetes the intramolecular deactivation over a broad range of temperatures, highlighting the potential of [Fe$^{III}$(phtmeimb)$_{2}$]PF$_{6}$ to perform photocatalytic bimolecular reactions

Drastic difference between hole and electron injection through the gradient shell of CdxSeyZn1−xS1−y quantum dots

Ultrafast fluorescence spectroscopy was used to investigate the hole injection in Cd x Se y Zn 1−x S 1−y gradient core–shell quantum dot sensitized NiO photocathodes

Charge separation: From the topology of molecular electronic transitions to the dye/semiconductor interfacial energetics and kinetics

Charge separation properties, that is the ability of a chromophore, or a chromophore/semiconductor interface, to separate charges upon light absorption, are crucial characteristics for an efficient photovoltaic device. Starting from this concept, we devote the first part of this book chapter to the topological analysis of molecular electronic transitions induced by photon capture. Such analysis can be either qualitative or quantitative, and is presented here in the framework of the reduced density matrix theory applied to single-reference, multiconfigurational excited states. The qualitative strategies are separated into density-based and wave function-based approaches, while the quantitative methods reported here for analysing the photoinduced charge transfer nature are either fragment-based, global or statistical. In the second part of this chapter we extend the analysis to dye-sensitized metal oxide surface models, discussing interfacial charge separation, energetics and electron injection kinetics from the dye excited state to the semiconductor conduction band states

Photoredox Catalysts Based on Earth-abundant Metal Complexes

We would like to thank the Engineering and Physical Sciences Research Council and CRITICAT Centre for Doctoral Training for financial support [Ph.D. studentship to B.H.; Grant code: EP/L016419/1]. C.L thanks the Prof. & Mrs Purdie Bequests Scholarship and AstraZeneca for his PhD Studentship.Over the last decade, visible light photoredox catalysis has exploded into the consciousness of the synthetic chemist. The principal photocatalysts used are based on rare and toxic ruthenium(II) and iridium(III) complexes. This critical review focusses on Earth-abundant metal complexes as potential replacement photocatalysts and summarizes the use of photoactive Cu(I), Zn(II), Ni(0), V(V), Zr(IV), W(0), W(VI), Mo(0), Cr(III) , Co(III) and Fe(II) complexes in photoredox reactions. The optoelectronic properties of these complexes and relevant structurally related analogs, not yet used for photoredox catalysis, are disccussed in combination with the reaction scope reported for each photocatalyst. Prospects for the future of photocatalyst design are considered.PostprintPeer reviewe

The nature of singlet exciton fission in carotenoid aggregates.

Singlet exciton fission allows the fast and efficient generation of two spin triplet states from one photoexcited singlet. It has the potential to improve organic photovoltaics, enabling efficient coupling to the blue to ultraviolet region of the solar spectrum to capture the energy generally lost as waste heat. However, many questions remain about the underlying fission mechanism. The relation between intermolecular geometry and singlet fission rate and yield is poorly understood and remains one of the most significant barriers to the design of new singlet fission sensitizers. Here we explore the structure-property relationship and examine the mechanism of singlet fission in aggregates of astaxanthin, a small polyene. We isolate five distinct supramolecular structures of astaxanthin generated through self-assembly in solution. Each is capable of undergoing intermolecular singlet fission, with rates of triplet generation and annihilation that can be correlated with intermolecular coupling strength. In contrast with the conventional model of singlet fission in linear molecules, we demonstrate that no intermediate states are involved in the triplet formation: instead, singlet fission occurs directly from the initial 1B(u) photoexcited state on ultrafast time scales. This result demands a re-evaluation of current theories of polyene photophysics and highlights the robustness of carotenoid singlet fission.This work was supported by the EPSRC (UK) (EP/G060738/ 1), the European Community (LASERLAB-EUROPE, grant agreement no. 284464, EC’s Seventh Framework Programme; and Marie-Curie ITN-SUPERIOR, PITN-GA-2009-238177), and the Winton Programme for the Physics of Sustainability. G.C. acknowledges support by the European Research Council Advanced Grant STRATUS (ERC-2011-AdG No. 291198). J.C. acknowledges support by the Royal Society Dorothy Hodgkin Fellowship and The University of Sheffield’s Vice- Chancellor’s Fellowship scheme.This is the final published version. It was first made available by ACS at http://pubs.acs.org/doi/abs/10.1021/jacs.5b01130

Preservation of mining limits and their consequences for the state and the region

Import 22/07/2015Diplomová práce popisuje v úvodní části důvody vzniku územních ekologických limitů těžby, vymezuje těžbou zasažené lokality a rozsah těžby v případě zachování nebo prolomení územních ekologických limitů těžby. V obecné rovině seznamuje s těžebními společnostmi, které v regionu těžbu provádí a podrobněji popisuje společnost Severní energetická a. s., která těží hnědé uhlí v nejvíce limity dotčeném lomu ČSA. Diplomová práce též charakterizuje region bývalého okresu Most, který je těžbou hnědého uhlí zasažen nejvíce. Praktická část diplomové práce je zaměřena na vývoj a ekonomické zhodnocení možných výdajů státu, které vzniknou v případě, že územní ekologické limity těžby zůstanou zachovány a na možný vývoj v regionu, který byl po dlouhá desetiletí těžbou hnědého uhlí zasažen.The thesis describes in the introduction the reasons for the emergence of territorial environmental limits, it defines the mining sites affected and the extent of mining in the event of maintaining or breaking the territorial environmental limits. Commonly along with other mining companies in the region extraction is also carried out but specifically by the company Severní energetická a. s., which mines brown coal within the most affected ČSA limits. The thesis also describes the region of the former district of Most, which is most affected by the coal-mining industry. The practical part of the thesis is focused on the development and economic evaluation of potential state expenditure incurred in the event that local ecological mining limits will remain a possible development in the region, which was for decades the mining of brown coal impacted.Prezenční545 - Institut ekonomiky a systémů řízenívelmi dobř

STUDIUM ZÁKLADNÍCH MECHANISMŮ PERITONEÁLNÍHO ZÁNĚTU U CANDÁTA OBECNÉHO (Sander lucioperca)

Pike-perch (Sander lucioperca) is a species of fish whose breeding in recirculation systems has a great prospect in the years to come. Due to the unfavorable conditions of intensive rearing of these fish in recirculation systems, they are often exposed to stress resulting in reduced fish defenses. Thus, fish are exposed to attack of a wide range of bacteria. Although there are preventive measures to protect fish against pathogen attack, knowledge of the immune system and the immune response of the fish is crucial for further evolution of vaccination. Even though we know the mechanisms of immune response of many fish species,but the knowledge of the pike-perch's immune response is very limited