Photophysical and Electrochemical Properties of meso-Substituted Thien-2-yl Zn(II) Porphyrins

The influence of the thiophene ring on the ground and excited state properties of the porphyrin ring is investigated, when substituted at the meso-position. A series of mono-, di-, tri-, and tetra-meso-thien-2-yl porphyrins are studied and discussed with respect to the reference compounds zinc(II)-5,10,15,20-tetra(thien-2′-yl)porphyrin (1a) and zinc(II)-5,10,15,20-tetraphenylporphyrin (ZnTPP). The extended conjugated system zinc(II)-5-(5′-(5′′-ethynyl-2′′-thiophenecarboxaldehyde)thien-2′-yl)-10,15,20-triphenylporphyrin (4d) is also studied and shows enhanced charge transfer character due to the presence of the terminal aldehyde accepting group. A detailed analysis of ground and excited state UV−vis absorption, steady-state and time-resolved fluorescence, laser flash photolysis, and electrochemical data all point toward substantial electronic communication between the central Zn(II) porphyrin ring and the meso-thien-2-yl substituents, which is evident from excited state charge transfer character

Redox control of meso-Zinc(II) ferrocenylporphyrin based fluorescence switches

The switching on and off of porphyrin fluorescence is achieved through the use of the ferrocene/ferrocenium redox couple. This approach makes use of the quenching of the porphyrin fluorescence by excited-state electron transfer from the ferrocene to the porphyrin, a process that, in the present systems, can be “switched on”, reversibly, by oxidation to the ferrocenium ion

A real options based decision support tool for R&D investment: application to CO2 recycling technology

We propose a practice relevant real options based decision support tool to aid in the practical evaluation of R&D investments in technology. Using a Poisson process to simulate the discrete progress typical of advancements in R&D, we take explicit account of the technical risk of the technology development, while market risk exposure and the effect of learning-by-doing through operating the technology is also explicitly modelled. We present a compound real option design, where a European real option structure is used to model the fixed length term typical of early phase research, which is exercisable into an American real option structure to model a subsequent phase R&D. In this latter phase, a successful outcome is acted upon immediately to operationalise the technology. We propose a simulation approach, which models R&D progress in a stylised logistic function or ’S-shape’ form, capturing the typically slow rate of R&D progress at the start of the early phase, through to more rapid improvement as the R&D advances, which then slows again as the limitations of the R&D are approached. We propose a business appropriate and workable economic meaning to this progress in the R&D process. We demonstrate the decision support tool with an application to evaluating the R&D investment potential in CO2 recycling technology, where an energy commodity is produced

CHAPTER 12: Metallosupramolecular assemblies for application as photocatalysts for the production of solar fuels

There is much interest around metallosupramolecular materials because of their use in magnetic, photonic and electronic materials. The book first highlights naturally occurring functional metallosupramolecular materials, with subsequent chapters covering the numerous potential applications of such materials in a systematic fashion. This provides the reader with a comprehensive overview of the applications of this class of materials, including the chemistry underlying the synthesis of a variety of ligands. The book will be of interest to graduate students, academics and industrial chemists interested in supramolecular chemistry, materials science and the materials applications

A Matrix Isolation and Flash Photolysis Study of the Cyclization Reactions of Chromium Amino Carbenes

The photochemistry of chromium amino carbene complexes have been studied using IR and UV–vis spectroscopy in matrices at 12 K and using UV–vis spectroscopy following laser flash photolysis in solution at room temperature (r.t.). The complexes studied can be divided into two classes. The Class 1 complexes are (CO)5Cr[C(NMe2)Me], (CO)5Cr[C(NBz2)Me], (CO)5Cr[C(NMe2)Ph] which are known to have a low or no photo-reactivity with imines to form β-lactams. Class 2 complexes are (CO)5Cr[C(NMe2)H], (CO)5Cr[C(NBz2)H], (CO)5Cr[C(NH2)Me] and these complexes are known to undergo efficient photochemical reactions with imines to form β-lactams. The proposed active intermediate in the reaction to form β-lactams is a metal ketene complex. For both classes of complexes no ketene complex was observed upon irradiation in either the cryogenic matrix or the solution studies. The only photochemical process which was observed in all experiments was CO loss and the major product for all complexes was assigned to be cis-(CO)4Cr[(N(R2)R′]. This species behaved differently for the two classes of complexes. In the matrix isolation experiments on Class 2 complexes this species reacted with N2, ethene or CO present in the matrix cage, whereas for Class 1 complexes it did not. In the flash photolysis studies on Class 1 complexes the rate of reaction of this transient species with CO showed only a moderate dependence on the nature of the solvent. The rate of reaction for the same process measured for the transient species formed from Class 2 complexes showed a significantly greater dependence on the solvent. We propose that for Class 1 complexes the vacant site formed by photo-dissociation of a cis-CO ligand is blocked, whereas for the Class 2 complexes it is not. Therefore, in the latter case the site is open to reaction with active species in the cryogenic matrices and the solvent acts as a ‘token’ ligand in the solution studies. The difference in the reactivity of cis-(CO)4Cr[C(NR2)R′] for the two classes of complex may aid the explanation of the differences in their synthetic photochemistry

Recent progress in the development of bimetallic photocatalysts for hydrogen generation

In this contribution recent developments in the design and application of bimetallic photocatalysts for the generation of hydrogen via intramolecular processes are assessed. The basic concepts of such assemblies are discussed together with an overview of the factors and molecular issues that affect their potential as photocatalysts. Issues that so far have limited progress are discussed and suggestions for future directions are made

Dye sensitised solar cells with nickel oxide photocathodes prepared via scalable microwave sintering

Photoactive NiO electrodes for cathodic dye-sensitised solar cells (p-DSCs) have been prepared with thicknesses ranging between 0.4 and 3.0 mm by spray-depositing pre-formed NiO nanoparticles on fluorine-doped tin oxide (FTO) coated glass substrates. The larger thicknesses were obtained in sequential sintering steps using a conventional furnace (CS) and a newly developed rapid discharge sintering (RDS) method. The latter procedure is employed for the first time for the preparation of p-DSCs. In particular, RDS represents a scalable procedure that is based on microwave-assisted plasma formation that allows the production in series of mesoporous NiO electrodes with large surface areas for p-type cell photocathodes. RDS possesses the unique feature of transmitting heat from the bulk of the system towards its outer interfaces with controlled confinement of the heating zone. The use of RDS results in a drastic reduction of processing times with respect to other deposition methods that involve heating/calcination steps with associated reduced costs in terms of energy. P1-dye sensitized NiO electrodes obtained via the RDS procedure have been tested in DSC devices and their performances have been analysed and compared with those of cathodic DSCs derived from CS-deposited samples. The largest conversion efficiencies (0.12%) and incident photon-to-current conversion efficiencies, IPCEs (50%), were obtained with sintered NiO electrodes having thicknesses of B1.5–2.0 mm. In all the devices, the photogenerated holes in NiO live significantly longer (th B 1 s) than have previously been reported for P1-sensitized NiO photocathodes. In addition, P1-sensitised sintered electrodes give rise to relatively high photovoltages (up to 135 mV) when the triiodide–iodide redox couple is used.Science Foundation IrelandKnut and Alice Wallenberg FoundationSwedish Energy AgencyRoyal Society for ChemistryAM

Synthesis, Photo-, and Electrochemistry of Ruthenium Bis(bipyridine) Complexes Comprising a N-heterocyclic Carbene Ligand

Analogues of [Ru(bpy)3]2+ were prepared in which one pyridine ligand site is substituted by a N-heterocyclic carbene (NHC) ligand, that is, either by an imidazolylidene with a variable wingtip group R (R = Me, 3a; R = Et, 3b; R = iPr, 3c), or by a benzimidazolylidene (Me wingtip group, 3d), or by a 1,2,3-triazolylidene (Me wingtip group, 3e). All complexes were characterized spectroscopically, photophysically, and electrochemically. An increase of the size of the wingtip groups from Me to Et or iPr groups distorts the octahedral geometry (NMR spectroscopy) and curtails the reversibility of the ruthenium oxidation. NHC ligands with methyl wingtip groups display reversible ruthenium oxidation at a potential that reflects the donor properties of the NHC ligand (triazolylidene > imidazolylidene > benzimidazolylidene). The most attractive properties were measured for the triazolylidene ruthenium complex 3e, featuring the smallest gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the series (2.41 eV), a slightly red-shifted absorption profile, and reasonable excited-state lifetime (188 ns) when compared to [Ru(bpy)3]2+. These features demonstrate the potential utility of triazolylidene ruthenium complexes as photosensitizers for solar energy conversion.European Research CouncilScience Foundation Irelan