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Advanced radiation therapy requires advanced instrumentation for dose delivery and beam monitoring. On the other side, research and development of state-of-the-art radiation detectors require research and the development of advanced techniques and instrumentation for characterizing these detectors. The newly developed timing sensors with good spatial and timing resolution, such as low gain avalanche diodes, become very attractive devices to be exploited and integrated in an innovative way into pCT, PET systems, or some other hybrid technologies for microdosimetry. For this purpose, a high fill factor (the ratio of the active area and the total sensor area) and excellent isolation of pixels must be achieved. In the scope of study of the region between the two pixels, the two characterization techniques are presented in this paper: ion beam induced charge (IBIC) and two-photon absorption-transient current technique (TPA-TCT). The accuracy of methods and the precision of the measurements of the interpad distance (IP) are investigated by comparing the experimental data to the nominal values provided by vendors of the prototypes. [ABSTRACT FROM AUTHOR]

We present an in-depth investigation of the interpad (IP) gap region in the ultra-fast silicon detector (UFSD) Type 10, utilizing a femtosecond laser beam and the transient current technique (TCT) as probing instruments. The sensor, fabricated in the trench-isolated TI-LGAD RD50 production batch at the FBK Foundry, enables a direct comparison between TI-LGAD and standard UFSD structures. This research aims to elucidate the isolation structure in the IP region and measure the IP distance between pads, comparing it to the nominal value provided by the vendor. Our findings reveal an unexpectedly strong signal induced near p-stops. This effect is amplified with increasing laser power, suggesting significant avalanche multiplication, and is also observed at moderate laser intensity and high HV bias. This investigation contributes valuable insights into the IP region's isolation structure and electric field effects on charge collection, providing critical data for the development of advanced sensor technology for the Compact Muon Selenoid (CMS) experiment and other high-precision applications. [ABSTRACT FROM AUTHOR]

We present a setup for time-resolved spectroscopic ellipsometry in a pump–probe scheme using femtosecond laser pulses. As a probe, the system deploys supercontinuum white light pulses that are delayed with respect to single-wavelength pump pulses. A polarizer–sample–compensator–analyzer configuration allows ellipsometric measurements by scanning the compensator azimuthal angle. The transient ellipsometric parameters are obtained from a series of reflectance-difference spectra that are measured for various pump–probe delays and polarization (compensator) settings. The setup is capable of performing time-resolved spectroscopic ellipsometry from the near-infrared through the visible to the near-ultraviolet spectral range at 1.3 eV–3.6 eV. The temporal resolution is on the order of 100 fs within a delay range of more than 5 ns. We analyze and discuss critical aspects such as fluctuations of the probe pulses and imperfections of the polarization optics and present strategies deployed for circumventing related issues. [ABSTRACT FROM AUTHOR]

Gain suppression effects and destructive events caused by highly energetic single particles should be considered for the operation of LGADs in experiments. The performance of the LGADs depends on the particle's ionization density (energy loss) as well as incident angle, while large deposits of energy in the active zone of LGADs operated at high bias voltages can lead to the destructive break down of the sensor. Herein, we summarize the main findings from a study at the ELI Beamlines laser facility and from an ionized dense charge induced gain suppression (GS) study using a nuclear microbeam probe station and MeV ions at Ruder Boskovic Institute (RBI). The transient currents technique (TCT) with a fs-laser has been used for the SEB study, while the Ion Beam Induced Charge (IBIC) technique has been employed for the GS study. [ABSTRACT FROM AUTHOR]

A feasibility study conducted at the laser facility ELI Beamlines confirms that fs-laser pulses can produce Single Event Effect (SEE), Single Event Upset (SEU) and Single Event Burnout (SEB) conditions in irradiated Low Gain Avalanche Detectors (LGADs) and the corresponding PIN diodes. A comprehensive and systematic study on PIN and LGAD mortality has been conducted to experimentally determine the stability, instability, and irreversible damage thresholds for LGADs and PINs exploiting a fs-laser system. Thresholds are given as sets of two parameters: bias voltage and laser pulse energy (energy deposition threshold). Using the Two-Photon Absorption (TPA) - Transient Current Technique (TCT) to study the mechanism that triggers SEU/SEB conditions in LGADs, as a function of illumination position establishes this technique as a promising tool for more advanced explorations of SEE, not only in LGADs but also in other Si-based sensors. To achieve these results, a highly flexible and versatile fs-laser-based TCT experimental setup has been developed at ELI Beamlines, allowing two TCT modalities with the same setup: Single Photon Absorption (SPA) at 800 nm laser wavelength and TPA at 1550 nm. [ABSTRACT FROM AUTHOR]

The covalent photoadduct (PA) between [Ru(TAP)3]2+ (TAP = 1,4,5,8-tetraazaphenanthrene) and guanosine monophosphate (GMP) opened the way to interesting photobiological applications. In this context, the PA's capability upon illumination to give rise to the addition of a second guanine base is especially interesting. The origins of these intriguing properties are for the first time thoroughly investigated by an experimental and theoretical approach. The PA's spectroscopic and redox data combined with TDDFT results corroborated with resonance Raman data show that the properties of this PA (pK a around 7) depend on the solution pH. Theoretical results indicate that the acid form PA.H + when excited should relax to MLCT (metal-to-ligand charge transfer) excited states, in contrast to the basic form PA whose excited state should have LLCT/ILCT (ligand-to-ligand charge transfer/intra ligand charge transfer) characteristics. Ultrafast excitation of PA.H + at pH 5.9 produces continuous dynamic processes in a few hundred picoseconds involving coupled proton-electron transfers responsible for luminescence quenching. Long-lived species of a few microseconds capable of reacting with GMP are produced at that pH, in agreement with the formation of covalent addition of a second GMP to PA, as shown by mass spectrometry results. In contrast, at pH 8 (mainly nonprotonated PA), other ultrafast transient species are detected and no GMP biadduct is formed in the presence of GMP. This pH dependence of photoreaction can be rationalized with the different nature of the excited states, thus at pH 8, unreactive LLCT/ILCT states and at pH 5.9 reactive MLCT states. [ABSTRACT FROM AUTHOR]

Thefirst systematic steady-state and time-resolved emission studyof firefly oxyluciferin (emitter in firefly bioluminescence) and itsanalogues in aqueous buffers provided the individual emission spectraof all chemical forms of the emitter and the excited-state equilibriumconstants in strongly polar environment with strong hydrogen bondingpotential. The results confirmed the earlier hypothesis that excited-stateproton transfer from the enol group is favored over proton transferfrom the phenol group. In water, the phenol-keto form is the strongestphotoacid among the isomers and its conjugate base (phenolate-keto)has the lowest emission energy (634 nm). Furthermore, for the firsttime we observed green emission (525 nm) from a neutral phenol-ketoisomer constrained to the keto form by cyclopropyl substitution. Theorder of emission energies indicates that in aqueous solution a seconddeprotonation at the phenol group after the enol group had dissociated(that is, deprotonation of the phenol-enolate) does not occur in thefirst excited state. The pH-dependent emission spectra and the time-resolvedfluorescence parameters revealed that the keto-enol tautomerism reaction,which can occur in a nonpolar environment (toluene) in the presenceof a base, is not favored in water. [ABSTRACT FROM AUTHOR]

The effects of the nonprotonated and protonated calix[6]crypturea 1/1•H+ on the PF6- and Cl- salts of a luminescent Ru-TAP complex (TAP = 1,4,5,8-tetraazaphenanthrene) were investigated. Thus, the phototriggered basic properties of this complex were examined with 1•H+ in acetonitrile (MeCN) and butyronitrile (BuCN). The Ru excited complex was shown to be able to extract a proton from the protonated calixarene, accompanied by a luminescence quenching in both solvents. However, in BuCN, the Cl- salt of the complex exhibited a surprising behavior in the presence of 1/1•H+. Although an emission decrease was observed with the protonated calixarene, an emission increase was evidenced in the presence of nonprotonated 1. As the Cl- ions were shown to inhibit the luminescence of the complex in BuCN, this luminescence increase by nonprotonated 1 was attributed to the protection effect of 1 by encapsulation of the Cl- anions into the tris-urea binding site. The study of the luminescence lifetimes of the Ru-TAP complex in BuCN as a function of temperature for the PF6- and Cl- salts in the absence and presence of 1 led to the following conclusions. In BuCN, in contrast to MeCN, in addition to ion pairing, because of the poor solvation of the ions, the luminescent metal-to-ligand charge transfer (³MLCT) state could reach two metal-centered (³MC) states, one of which is in equilibrium with the ³MLCT state during the emission lifetime. The reaction of Cl- with this latter ³MC state would be responsible for the luminescence quenching, in agreement with the formation of photosubstitution products. [ABSTRACT FROM AUTHOR]

We recently published a study concerning femtosecond pump–probe absorption edge spectroscopy of cubic GaN (fundamental bandgap: 3.23 eV), resulting in the transient dielectric function. In the present study, we continue our investigations of those pump–probe measurements by determining the time-dependent transition energy at the Fermi-vector between the conduction and valence bands. The generation of electron–hole pairs by the 266 nm pump-beam (4.66 eV) shifts the absorption edge by ≈ 500 meV within 1 ps due to many-body effects like band-filling and bandgap renormalization. Modeling this ultra-fast change is achieved by converting the transition energies into free-carrier concentrations, assuming the electron contributions to be dominant. We consider the relaxation, recombination, and diffusion of those free-carriers as well as either an additional gain-recombination or temperature effects. This allows for describing the transition energies on short time scales. Both models yield similar values for the characteristic relaxation time (≈ 0.21 ps), recombination time (≈ 25 ps), and diffusion coefficient (≈ 1 cm 2 /s). [ABSTRACT FROM AUTHOR]

An ultra-fast change of the absorption onset for zincblende gallium-nitride (zb-GaN) (fundamental bandgap: 3.23 eV) is observed by investigating the imaginary part of the dielectric function using time-dependent femtosecond pump–probe spectroscopic ellipsometry between 2.9 and 3.7 eV. The 266 nm (4.66 eV) pump pulses induce a large electron–hole pair concentration up to 4 × 10 20 cm − 3 , which shift the transition energy between conduction and valence bands due to many-body effects up to ≈ 500 meV. Here, the absorption onset increases due to band filling while the bandgap renormalization at the same time decreases the bandgap. Additionally, the absorption of the pump-beam creates a free-carrier profile within the 605 nm zb-GaN layer with high free-carrier concentrations at the surface, and low concentrations at the interface to the substrate. This leads to varying optical properties from the sample surface (high transition energy) to substrate (low transition energy), which are taken into account by grading analysis for an accurate description of the experimental data. For this, a model describing the time- and position-dependent free-carrier concentration is formulated by considering the relaxation, recombination, and diffusion of those carriers. We provide a quantitative analysis of optical experimental data (ellipsometric angles Ψ and Δ) as well as a plot for the time-dependent change of the imaginary part of the dielectric function. [ABSTRACT FROM AUTHOR]

Rh and Ir complexes that contain meso-( p-methoxyphenyl)dipyrromethene (dipy) and phenylpyridine (ppy) ligands {i.e., [Rh(dipy)3], [Rh(ppy)2(dipy)] and [Ir(ppy)2(dipy)]} have been prepared and their electrochemical and luminescence behaviour are discussed and compared to results of theoretical calculations. The oxidation and reduction potentials, in agreement with the time-dependent (TD)-DFT calculations, indicate clearly that the HOMO-LUMO transitions are governed by the dipy ligand, which controls also the triplet excited-state emission. However, in luminescence, the two Rh complexes exhibit, in addition to a dipy-centred triplet emission, luminescence from the singlet excited state, which predominates at room temperature, due to a less important influence of the heavy-metal effect in Rh than in Ir complexes. Although the TD-DFT results are in very good agreement with the experimental emission spectra from the dipy-centred triplet excited state, this is not the case for the absorption spectra of the complexes and free dipy ligand. [ABSTRACT FROM AUTHOR]

The photoreaction mechanism of [Ru(TAP)2(phen)]2+ and [Ru(TAP)3]2+ (TAP = 1,4,5,8-tetraazaphenanthrene) with tryptophan (Trp), N-acetyl-Trp, and Lys-Trp-Lys is examined. The existence of a photoelectron-transfer process from the amino acid unit is demonstrated by laser flash photolysis experiments. The back electron transfer (BET) from the reduced complex to the oxidized amino acid, occurring at the microsecond time scale, corresponds approximately to an equimolecular-bimolecular process; however, it is disturbed by another reaction, originating from the oxidized Trp. Moreover, in competition with the BET, the reduced and oxidized intermediates give rise to an adduct. The latter is clearly detected by gel electrophoresis experiments in denaturing conditions, with a system composed of an oligonucleotide derivatized at the 3′ end by the RuIITAP complex and hybridized with the complementary sequence functionalized at the 5′ end by the tripeptide Lys-Trp-Lys. Thus, upon illumination, a cross-linking between the two strands is observed, which originates from the presence of a Trp residue. [ABSTRACT FROM AUTHOR]

Transient dielectric functions with a 120 fs time resolution of Ge, Si, and InP were acquired from 1.7 to 3.5 eV with a femtosecond pump-probe rotating-compensator ellipsometer. The intensity of the pump laser (with 1.55, 3.10, or 4.65 eV photon energy) was adjusted to create an initial near-surface carrier density of 1020 cm−3. In Ge, there is a significant (∼15%) decrease in the E1 and E1 + Δ1 critical point absorption and a Kramers–Kronig consistent change in the refractive index because photoexcited electrons at L block these transitions and reduce their amplitudes. Only a small redshift of the E1 critical point is observed, which we attribute to lattice heating and exchange-correlation effects. Minimal changes were found for Si and InP, where electrons near Δ and Γ do not participate in interband transitions between 1.7 and 3.5 eV. [ABSTRACT FROM AUTHOR]

Time-resolved femtosecond-stimulated Raman spectroscopy (FSRS) provides valuable information on the structural dynamics of biomolecules. However, FSRS has been applied mainly up to the nanoseconds regime and above 700 cm−1, which covers only part of the spectrum of biologically relevant time scales and Raman shifts. Here we report on a broadband (~200–2200 cm−1) dual transient visible absorption (visTA)/FSRS set-up that can accommodate time delays from a few femtoseconds to several hundreds of microseconds after illumination with an actinic pump. The extended time scale and wavenumber range allowed us to monitor the complete excited-state dynamics of the biological chromophore flavin mononucleotide (FMN), both free in solution and embedded in two variants of the bacterial light-oxygen-voltage (LOV) photoreceptor EL222. The observed lifetimes and intermediate states (singlet, triplet, and adduct) are in agreement with previous time-resolved infrared spectroscopy experiments. Importantly, we found evidence for additional dynamical events, particularly upon analysis of the low-frequency Raman region below 1000 cm−1. We show that fs-to-sub-ms visTA/FSRS with a broad wavenumber range is a useful tool to characterize short-lived conformationally excited states in flavoproteins and potentially other light-responsive proteins. [ABSTRACT FROM AUTHOR]

We recently reported a very efficient homogeneous system for visible-light driven hydrogen production in water based on the cobalt(III) tetraaza-macrocyclic complex [Co(CR)Cl 2 ] + ( 1 ) (CR = 2,12-dimethyl-3,7,11,17-tetra-azabicyclo(11.3.1)-heptadeca-1(17),2,11,13,15-pentaene) as a noble metal-free catalyst, with [Ru II (bpy) 3 ] 2+ ( Ru ) as photosensitizer and ascorbate/ascorbic acid (HA − /H 2 A) as a sacrificial electron donor and buffer ( PhysChemChemPhys 2013, 15, 17544). This catalyst presents the particularity to achieve very high turnover numbers (TONs) (up to 1000) at pH 4.0 at a relative high concentration (0.1 mM) generating a large amount of hydrogen and having a long term stability. A similar activity was observed for the aquo derivative [Co III (CR)(H 2 O) 2 ] 3+ ( 2 ) due to substitution of chloro ligands by water molecule in water. In this work, the geometry and electronic structures of 2 and its analog [Zn II (CR)Cl] + ( 3 ) derivative containing the redox innocent Zn(II) metal ion have been investigated by DFT calculations under various oxidation states. We also further studied the photocatalytic activity of this system and evaluated the influence of varying the relative concentration of the different components on the H 2 -evolving activity. Turnover numbers versus catalyst (TON Cat ) were found to be dependent on the catalyst concentration with the highest value of 1130 obtained at 0.05 mM. Interestingly, the analogous nickel derivative, [Ni II (CR)Cl 2 ] ( 4 ), when tested under the same experimental conditions was found to be fully inactive for H 2 production. Nanosecond transient absorption spectroscopy measurements have revealed that the first electron-transfer steps of the photocatalytic H 2 -evolution mechanism with the Ru /cobalt tetraaza/HA − /H 2 A system involve a reductive quenching of the excited state of the photosensitizer by ascorbate ( k q = 2.5 × 10 7 M − 1 s − 1 ) followed by an electron transfer from the reduced photosensitizer to the catalyst ( k et = 1.4 × 10 9 M − 1 s − 1 ). The reduced catalyst can then enter into the cycle of hydrogen evolution. [ABSTRACT FROM AUTHOR]

We present an investigation of the interpad region (IP) in the Ultra-Fast Silicon Detector (UFSD) Type 10, utilizing a femtosecond laser and the transient current technique (TCT). We elucidate the isolation structure and measure the IP distance between pads, comparing it to the nominal value provided by the vendor. A comparison of sensors with identical layouts but different nominal IP distances (49 μm vs. 61 μm) and different processing parameters revealed their significant different charge collection properties in the IP. • fs-laser TCT can characterize the isolation structures of the segmented LGADs. • Charge multiplication is observed in the interpad region of the segmented LGADs. • The strongest interpad charge multiplication is observed close to p-stop implants. • Interpad length and doping are critical for charge multiplication between the pads. • Drop in interpad gap and increase of doping boost interpad charge multiplication. [ABSTRACT FROM AUTHOR]

Herein, the complex pseudodielectric function of Ge and Si from femtosecond pump–probe spectroscopic ellipsometry with 267, 400, and 800 nm pump–pulse wavelengths is analyzed by fitting analytical lineshapes to the second derivatives of the pseudodielectric function with respect to energy. This yields the critical point parameters (threshold energy, lifetime broadening, amplitude, and excitonic phase angle) of E1 and E1+Δ1 in Ge and E1 in Si as functions of delay time. Coherent longitudinal acoustic phonon oscillations with a period of about 11 ps are observed in the transient critical point parameters of Ge. From the amplitude of these oscillations, the laser‐induced strain is found to be on the order of 0.03% for Ge measured with the 800 nm pump pulse, which is in reasonable agreement with the strain calculated from theory. [ABSTRACT FROM AUTHOR]

The chemical complexity of oxyluciferin (OxyLH2), the light-emitting molecule in the bioluminescence of fireflies, originates from the possibility of keto/enol tautomerism and single or double deprotonation. Herein, we present detailed infrared spectroscopic analysis of OxyLH2 and several of its chemical isomers and isotopomers. To facilitate the future characterization of its biogenic forms, we provide accurate assignments of the solid-state and solution FTIR spectra of OxyLH2 based on comparison to six isotopically labeled variants ([2-13C]-OxyLH2, [3-15N]-OxyLH2, [4-13C]-OxyLH2, [5-13C]-OxyLH2, [2′-13C]-OxyLH2, [3′-15N]-OxyLH2), five closely related structural analogues, and theoretically computed spectra. The computed DFT harmonic vibrational force fields (B3LYP and M06 functionals with basis sets of varying flexibility up to 6-311++G**) reproduce well the observed shifts in the IR spectra of both isotopically labeled and structurally related analogues. [ABSTRACT FROM AUTHOR]

Using the HETPHEN approach, five new heteroleptic copper(i) complexes composed of a push–pull 4,4′-styryl-6,6′-dimethyl-2,2′-bipyridine ligand and a bulky bis[(2-diphenylphosphino)phenyl]-ether (DPEphos) or a bis2,9-mesityl phenanthroline (Mes2Phen) were prepared and characterized by electronic absorption spectroscopy, electrochemistry, and TD-DFT calculations. These complexes exhibit very intense absorption bands in the visible region with extinction coefficient in the range of 5–7 × 104 M−1 cm−1. The analysis of the position, intensity and band shape indicates a strong contribution from an intra-ligand charge-transfer transition centered on the styrylbipyridine ligand along with MLCT transitions. These new complexes experimentally demonstrate that good light harvesting properties with bis-diimine copper(i) complexes are a reality if one chooses suitable ligands in the coordination sphere. This constitutes a milestone towards using bis-diimine copper(i) complexes for solar energy conversion (artificial photosynthesis and solar cells). [ABSTRACT FROM AUTHOR]

We report on the status of a users' end-station, MAC: a Multipurpose station for Atomic, molecular and optical sciences and Coherent diffractive imaging, designed for studies of structure and dynamics of matter in the femtosecond time-domain. MAC is located in the E1 experimental hall on the high harmonic generation (HHG) beamline of the ELI Beamlines facility. The extreme ultraviolet beam from the HHG beamline can be used at the MAC end-station together with a synchronized pump beam (which will cover the NIR/Vis/UV or THz range) for time-resolved experiments on different samples. Sample delivery systems at the MAC end-station include a molecular beam, a source for pure or doped clusters, ultrathin cylindrical or flat liquid jets, and focused beams of substrate-free nanoparticles produced by an electrospray or a gas dynamic virtual nozzle combined with an aerodynamic lens stack. We further present the available detectors: electron/ion time-of-flight and velocity map imaging spectrometers and an X-ray camera, and discuss future upgrades: a magnetic bottle electron spectrometer, production of doped nanodroplets and the planned developments of beam capabilities at the MAC end-station. [ABSTRACT FROM AUTHOR]

A new modification of a table‐top laser‐driven water‐jet plasma X‐ray source has been successfully implemented and commissioned at the Extreme Light Infrastructure (ELI) Beamlines user facility. In order to preserve the broadband nature of the source for spectroscopic experiments, a polycapillary lens was initially chosen as the focusing element. Generally, polycapillary X‐ray optics have a narrow photon acceptance angle and small field of view, making alignment complicated and time‐consuming. This contribution demonstrates a straightforward, reliable and reproducible procedure for aligning polycapillary focusing optics with broadband X‐rays. The method involves a pre‐alignment step where two X‐ray slits are mounted orthogonally on opposite sides of a 3D‐printed cylindrical polycapillary holder. This helps to precisely determine the optical axis of the X‐ray beam. Subsequent mounting of the polycapillary in the pre‐aligned holder with the slits removed allowed for immediate transmission of the X‐ray photons through the optics and has provided a good starting point for fine alignment. [ABSTRACT FROM AUTHOR]

Many linked processes occur concurrently in strongly excited semiconductors, such as interband and intraband absorption, scattering of electrons and holes by the heated lattice, Pauli blocking, bandgap renormalization and the formation of Mahan excitons. In this work, we disentangle their dynamics and contributions to the optical response of a ZnO thin film. Using broadband pump-probe ellipsometry, we can directly and unambiguously obtain the real and imaginary part of the transient dielectric function which we compare with first-principles simulations. We find interband and excitonic absorption partially blocked and screened by the photo-excited electron occupation of the conduction band and hole occupation of the valence band (absorption bleaching). Exciton absorption turns spectrally narrower upon pumping and sustains the Mott transition, indicating Mahan excitons. Simultaneously, intra-valence-band transitions occur at sub-picosecond time scales after holes scatter to the edge of the Brillouin zone. Our results pave new ways for the understanding of non-equilibrium charge-carrier dynamics in materials by reliably distinguishing between changes in absorption coefficient and refractive index, thereby separating competing processes. This information will help to overcome the limitations of materials for high-power optical devices that owe their properties from dynamics in the ultrafast regime. [ABSTRACT FROM AUTHOR]

A series of [CoIII(N4Py)(X)](ClO4)n (X = Cl-, Br-, OH-, N3-, NCS--κN, n = 2: X = OH2, NCMe, DMSO-κO, n = 3) complexes containing the tetrapyridyl N5 ligand N4Py (N4Py = 1,1-di(pyridin-2-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine) has been prepared and fully characterized by infrared (IR), UV-visible, and NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HRESI-MS), elemental analysis, X-ray crystallography, and electrochemistry. The reduced Co(II) and Co(I) species of these complexes have been also generated by bulk electrolyses in MeCN and characterized by UV-visible and EPR spectroscopies. All tested complexes are catalysts for the photocatalytic production of H2 from water at pH 4.0 in the presence of ascorbic acid/ascorbate, using [Ru(bpy)3]2+ as a photosensitizer, and all display similar H2-evolving activities. Detailed mechanistic studies show that while the complexes retain the monodentate X ligand upon electrochemical reduction to Co(II) species in MeCN solution, in aqueous solution, upon reduction by ascorbate (photocatalytic conditions), [CoII(N4Py)(HA)]+ is formed in all cases and is the precursor to the Co(I) species which presumably reacts with a proton. These results are in accordance with the fact that the H2-evolving activity does not depend on the chemical nature of the monodentate ligand and differ from those previously reported for similar complexes. The catalytic activity of this series of complexes in terms of turnover number versus catalyst (TONCat) was also found to be dependent on the catalyst concentration, with the highest value of 230 TONCat at 5 × 10-6 M. As revealed by nanosecond transient absorption spectroscopy measurements, the first electron-transfer steps of the photocatalytic mechanism involve a reductive quenching of the excited state of [Ru(bpy)3]2+ by ascorbate followed by an electron transfer from [RuII(bpy)2(bpy•-)]+ to the [CoII(N4Py)(HA)]+ catalyst. The reduced catalyst then enters into the H2-evolution cycle. [ABSTRACT FROM AUTHOR]

The development of multicomponent molecular systems for the photocatalytic reduction of water to hydrogen has experienced considerable growth since the end of the 1970s. Recently, with the aim of improving the efficiency of the catalysis, single-component photocatalysts have been developed in which the photosensitizer is chemically coupled to the hydrogen-evolving catalyst in the same molecule through a bridging ligand. Until now, none of these photocatalysts has operated efficiently in pure aqueous solution: a highly desirable medium for energy-conversion applications. Herein, we introduce a new ruthenium-rhodium polypyridyl complex as the first efficient homogeneous photocatalyst for H2 production in water with turnover numbers of several hundred. This study also demonstrates unambiguously that the catalytic performance of such systems linked through a nonconjugated bridge is significantly improved as compared to that of a mixture of the separate components. [ABSTRACT FROM AUTHOR]

The development of multicomponent molecular systems for the photocatalytic reduction of water to hydrogen has experienced considerable growth since the end of the 1970s. Recently, with the aim of improving the efficiency of the catalysis, single-component photocatalysts have been developed in which the photosensitizer is chemically coupled to the hydrogen-evolving catalyst in the same molecule through a bridging ligand. Until now, none of these photocatalysts has operated efficiently in pure aqueous solution: a highly desirable medium for energy-conversion applications. Herein, we introduce a new ruthenium-rhodium polypyridyl complex as the first efficient homogeneous photocatalyst for H2 production in water with turnover numbers of several hundred. This study also demonstrates unambiguously that the catalytic performance of such systems linked through a nonconjugated bridge is significantly improved as compared to that of a mixture of the separate components. [ABSTRACT FROM AUTHOR]

We report a very efficient homogeneous system for the visible-light-driven hydrogen production in pure aqueous solution at room temperature. This comprises [RhIII(dmbpy)2Cl2]Cl ( 1) as catalyst, [Ru(bpy)3]Cl2 ( PS1) as photosensitizer, and ascorbate as sacrificial electron donor. Comparative studies in aqueous solutions also performed with other known rhodium catalysts, or with an iridium photosensitizer, show that 1) the PS1/ 1/ascorbate/ascorbic acid system is by far the most active rhodium-based homogeneous photocatalytic system for hydrogen production in a purely aqueous medium when compared to the previously reported rhodium catalysts, Na3[RhI(dpm)3Cl] and [RhIII(bpy)Cp*(H2O)]SO4 and 2) the system is less efficient when [IrIII(ppy)2(bpy)]Cl ( PS2) is used as photosensitizer. Because catalyst 1 is the most efficient rhodium-based H2-evolving catalyst in water, the performance limits of this complex were further investigated by varying the PS1/ 1 ratio at pH 4.0. Under optimal conditions, the system gives up to 1010 turnovers versus the catalyst with an initial turnover frequency as high as 857 TON h−1. Nanosecond transient absorption spectroscopy measurements show that the initial step of the photocatalytic H2-evolution mechanism is a reductive quenching of the PS1 excited state by ascorbate, leading to the reduced form of PS1, which is then able to reduce [RhIII(dmbpy)2Cl2]+ to [RhI(dmbpy)2]+. This reduced species can react with protons to yield the hydride [RhIII(H)(dmbpy)2(H2O)]2+, which is the key intermediate for the H2 production. [ABSTRACT FROM AUTHOR]

Two new sterically challenged diimine ligands L1 (2,9-dimesityl-2-(4′-bromophenyl)imidazo[4,5-f][1,10]phenanthroline) and L2 (3,6-di-n-butyl-11-bromodipyrido[3,2-a:2′,3′-c]phenazine) have been synthesized with the aim to build original heteroleptic copper(I) complexes, following the HETPHEN concept developed by Schmittel and co-workers. The structure of L1 is based on a phen-imidazole molecular core, derivatized by two highly bulky mesityl groups in positions 2 and 9 of the phenanthroline cavity, preventing the formation of a homoleptic species, while L2 is a dppz derivative, bearing n-butyl chains in α positions of the chelating nitrogen atoms. The unambiguous formation of six novel heteroleptic copper(I) complexes based on L1, L2, and complementary matching ligands (2,9-R2-1,10-phenanthroline, with R = H, methyl, n-butyl or mesityl) has been evidenced, and the resulting compounds were fully characterized. The electronic absorption spectra of all complexes fits well with DFT calculations allowing the assignment of the main transitions. The characteristics of the emissive excited state were investigated in different solvents using time-resolved single photon counting and transient absorption spectroscopy. The complexes with ligand L2, bearing a characteristic dppz moiety, exhibit a very low energy excited-state which mainly leads to fast nonradiative relaxation, whereas the emission lifetime is higher for those containing the bulky ligand L1. For example, a luminescence quantum yield of about 3 × 10-4 is obtained with a decay time of about 50 ns for C2 ([CuI(nBu-phen)(L1)]+) with a weak influence of strong coordinating solvent on the luminescence properties. Overall, the spectral features are those expected for a highly constrained coordination cage. Yet, the complexes are stable in solution, partly due to the beneficial π stacking between mesityl groups and vicinal phenanthroline aromatic rings, as evidenced by the X-ray structure of complex C3 ([CuI(Mes-phen)(L2)]+). Electrochemistry of the copper(I) complexes revealed reversible anodic behavior, corresponding to a copper(I) to copper(II) transition. The half wave potentials increase with the steric bulk at the level of the copper(I) ion, reaching a value as high as 1 V vs SCE, with the assistance of ligand induced electronic effects. L1 and L2 are further end-capped by a bromo functionality. A Suzuki cross-coupling reaction was directly performed on the complexes, in spite of the handicapping lability of copper(I)-phenanthroline complexes. [ABSTRACT FROM AUTHOR]

The orange carotenoid protein (OCP) is a structurally and functionally modular photoactive protein involved in cyanobacterial photoprotection. Recently, based on bioinformatic analysis and phylogenetic relationships, new families of OCP have been described, OCP2 and OCPx. The first characterization of the OCP2 showed both faster photoconversion and back-conversion, and lower fluorescence quenching of phycobilisomes relative to the well-characterized OCP1. Moreover, OCP2 is not regulated by the fluorescence recovery protein (FRP). In this work, we present a comprehensive study combining ultrafast spectroscopy and structural analysis to compare the photoactivation mechanisms of OCP1 and OCP2 from Tolypothrix PCC 7601. We show that despite significant differences in their functional characteristics, the spectroscopic properties of OCP1 and OCP2 are comparable. This indicates that the OCP functionality is not directly related to the spectroscopic properties of the bound carotenoid. In addition, the structural analysis by X-ray footprinting reveals that, overall, OCP1 and OCP2 have grossly the same photoactivation mechanism. However, the OCP2 is less reactive to radiolytic labeling, suggesting that the protein is less flexible than OCP1. This observation could explain fast photoconversion of OCP2. Unlabelled Image • Excited-state dynamics of CAN is comparable in OCP1 and OCP2. • Photoactivation does not alter properties of ICT state of CAN. • CAN S* state identified exclusively in OCP2. • More constrained structure of CAN in OCP2 than in OCP1 • OCP2 is less flexible than OCP1. [ABSTRACT FROM AUTHOR]

The synthesis, reactivity and properties of a series of four polypyridyl ruthenium complexes have been studied. These complexes were used to post-functionalize preformed 3 nm silver and gold nanoparticles (NPs) in water and in dichloromethane (DCM). We studied the influence of the grafted complexes on the formation process and stability of the colloidal solutions and we investigated the optical and electrochemical properties of the final nanocomposites. Among the series of four ruthenium complexes, three novel heteroleptic complexes (1 – 3) bearing one pyridine, one amine or two carboxydithioic acid pendant groups were synthesized and reacted with preformed Au-NPs and Ag-NPs. Results were compared to those obtained with the model [Ru(bpy) 3 2+ complex (4). The strength of the interaction between the anchoring group and the surface of NPs influenced the size, shape and stability of the final nanocomposites. Polar solvent such as water induced aggregation and lead to unstable nanocomposites. Stationary and time resolved luminescence of grafted nanocomposites (1–3) showed that the luminescence of complexes were completely quenched (lifetime and emission quantum yield) in water by electron transfer processes, moreover electrical measurements rationalize that Ag nanocomposites exhibit the stronger quenching due to a lower oxidation potential. It also showed a current enhancement associated with double layer charging of the metal nanoparticle cores. Unlabelled Image • The synthesis of four polypyridyl ruthenium complexes was done. • The reactivity and properties of complexes have been studied. • Postfunctionalization of silver and gold nanoparticles was carried out. • Mutual influence between nanoparticles and the grafted complexes was investigated. [ABSTRACT FROM AUTHOR]