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4 páginas, 3 figuras.-- PACS numbers: 78.67.Wj, 71.35.Cc, 71.35.Lk, 73.22.Pr ; Using first principles many-body theory methods (GW+Bethe-Salpeter equation) we demonstrate that the optical properties of graphane are dominated by localized charge-transfer excitations governed by enhanced electron correlations in a two-dimensional dielectric medium. Strong electron-hole interaction leads to the appearance of small radius bound excitons with spatially separated electron and hole, which are localized out of plane and in plane, respectively. The presence of such bound excitons opens the path towards an excitonic Bose-Einstein condensate in graphane that can be observed experimentally. ; This work was supported by the Spanish MEC (FIS2007-65702-C02-01), ACI-Promociona (ACI2009- 1036) Grupos Consolidados UPV/EHU del Gobierno Vasco (IT-319-07), and the European Union through e-I3 ETSF project (Contract No. 211956). ; Peer reviewed

This is the peer-reviewed version of the following article: The Journal of Physical Chemistry B 2013, 117, 884–896, DOI:10.1021/jp311709c, which has been published in final form at https://pubs.acs.org/doi/abs/10.1021/jp311709c. This article may be used for non-commercial purposes only ; This paper deals with the interplay between solvent properties and isomerism of 2-(2′-hydroxyphenyl)imidazo[4,5-b]pyridine (1), and the proton and charge-transfer processes that the different isomers undergo in the first-excited singlet state. We demonstrate the strong influence of these processes on the fluorescence properties of 1. We studied the behavior of 1 in several neutral and acidified solvents, by UV–vis absorption spectroscopy and by steady-state and time-resolved fluorescence spectroscopy. The fluorescence of 1 showed a strong sensitivity to the environment. This behavior is the result of conformational and isomeric equilibria and the completely different excited-state behavior of the isomers. For both neutral and cationic 1, isomers with intramolecular hydrogen bond between the hydroxyl group and the benzimidazole N undergo an ultrafast excited-state intramolecular proton transfer (ESIPT), yielding tautomeric species with very large Stokes shift. For both neutral and cationic 1, isomers with the OH group hydrogen-bonded to the solvent behave as strong photoacids, dissociating in the excited state in solvents with basic character. The pyridine nitrogen exhibits photobase character, protonating in the excited state even in some neutral solvents. An efficient radiationless deactivation channel of several species was detected, which we attributed to a twisted intramolecular charge-transfer (TICT) process, facilitated by deprotonation of the hydroxyl group and protonation of the pyridine nitrogen ; This work has been supported by the Spanish Government and the European Regional Development Fund (Grant CTQ2010-17835) and the Xunta de Galicia (Grant CN 2012/314). A.B., M.V., and J.L.P.L. are thankful for a "Fundación ...

6 Figuras.- 1 Suplemento.- Título del pre-print: "Metallic and semiconducting carbon nanotube features observed in a hybrid titanium dioxide electrode".- This is the pre-peer reviewed version of the following article: ChemPhysChem 20: 838-847 (2019), which has been published in final form at DOI:10.1002/cphc.201900066. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. ; The transfer of nanoscale properties from single‐walled carbon nanotubes (SWCNTs) to macroscopic systems is a topic of intense research. In particular, inorganic composites of SWCNTs and metal oxide semiconductors are being investigated for applications in electronics, energy devices, photocatalysis, and electroanalysis. In this work, a commercial SWCNT material is separated into fractions containing different conformations. The liquid fractions show clear variations in their optical absorbance spectra, indicating differences in the metallic/semiconducting character and the diameter of the SWCNTs. Also, changes in the surface chemistry and the electrical resistance are evidenced in SWCNT solid films. The starting SWCNT sample and the fractions as well are used to prepare hybrid electrodes with titanium dioxide (SWCNT/TiO2). Raman spectroscopy reflects the optoelectronic properties of SWCNTs in the SWCNT/TiO2 electrodes, while the electrochemical behavior is studied by cyclic voltammetry. A selective development of charge transfer characteristics and double‐layer behavior is achieved through the suitable choice of SWCNT fractions. ; This work has been funded by the Spanish Ministry of Science and the European Regional Development Fund (ENE 2016‐79282‐C5‐1‐R), the Government of Aragon (T03‐17R), and the European Commission (H2020‐MSCA‐ITN‐2014‐ETN 642742 "Enabling Excellence"). ; Peer reviewed

A study on C9-imide acridinium photocatalysts with enhanced photoredox catalytic activity with respect to the well-established C9-mesityl acridinium salt is presented. The differences observed rely on the diverse accessibility of singlet chargetransfer excited states, which have been proven by CASPT2/CASSCF calculations, fluorescence and quenching studies ; The Boehringer Ingelheim Stiftung (Exploration Grant), the Deutsche Forschungsgemeinschaft (DFG), Spanish Government (CTQ2015-64561-R, CTQ2015-63997-C2, ENE2016-79608-C2-1-R) and Community of Madrid (2016-T1/AMB-1275) are acknowledged. The authors wish to thank ''Comunidad de Madrid'' for its support to the FotoArt-CM Project (S2018/NMT-4367) through the Program of R&D activities between research groups in Technologies 2013, co-financed by European Structural Fund

This work is supported by European Research Council (ERC) European Union Horizon 2020 (639846). The authors sincerely thank Koc University Boron and Advanced Materials Application and Research Center (KABAM) and Koc University Surface Science and Technology Center (KUYTAM) for the use of the facilities. We gratefully acknowledge the Center Research Laboratory at the University of Bayburt for TEM analysis. ; Capacitive charge transfer at the electrode/electrolyte interface is a biocompatible mechanism for the stimulation of neurons. Although quantum dots showed their potential for photostimulation device architectures, dominant photoelectrochemical charge transfer combined with heavy-metal content in such architectures hinders their safe use. In this study, we demonstrate heavy-metal-free quantum dot-based nano-heterojunction devices that generate capacitive photoresponse. For that, we formed a novel form of nano-heterojunctions using type-II InP/ZnO/ZnS core/shell/shell quantum dot as the donor and a fullerene derivative of PCBM as the electron acceptor. The reduced electron-hole wavefunction overlap of 0.52 due to type-II band alignment of the quantum dot and the passivation of the trap states indicated by the high photoluminescence quantum yield of 70% led to the domination of photoinduced capacitive charge transfer at an optimum donor-acceptor ratio. This study paves the way toward safe and efficient nanoengineered quantum dot-based next-generation photostimulation devices. ; European Research Council (ERC) 639846

Altres ajuts: we also acknowledge financial support from the Czech science foundation (20-08633X), MEYS project (LTC18039). The authors also acknowledge the assistance provided by the Research Infrastructures Nano-EnviCz (Project No. LM2015073) supported by the Ministry of Education, Youth and Sports of the Czech Republic and the project Pro-NanoEnviCz (Reg. No. CZ.02.1.01/0.0/0.0/ 16_013/0001821) supported by the Ministry of Education, Youth and Sports of the Czech Republic and the European Union - European Structural and Investments Funds in the frame of Operational Programme Research Development and Education. ; In the present work, the effect of doping on electronic properties in bulk purified and filled arc-discharge single-walled carbon nanotubes samples is studied for the first time by in situ Raman spectroelectrochemical method. A major challenge to turn the potential of SWCNTs into customer applications is to reduce or eliminate their contaminants by means of purification techniques. Besides, the endohedral functionalization of SWCNTs with organic and inorganic materials (i.e. metal halides) allows the development of tailored functional hybrids. Here, we report the purification and endohedral functionalization of SWCNTs with doping affecting the SWCNTs. Steam-purified SWCNTs have been filled with selected lutetium(iii) halides, LuCl, LuBr, LuI, and sealed using high-temperature treatment, yielding closed-ended SWCNTs with the filling material confined in the inner cavity. The purified SWCNTs were studied using TGA, EDX, STEM and Raman spectroscopy. The lutetium(iii) halide-filled SWCNTs (LuX@SWCNTs) were characterized using STEM, EDX, Raman spectroscopy and in situ Raman spectroelectrochemistry. It was found that there is a charge transfer between the SWCNTs and the encapsulated LuX (X = Cl, Br, I). The obtained data testify to the acceptor doping effect of lutetium(iii) halides incorporated into the SWCNT channels, which is accompanied by the charge transfer from nanotube walls to the introduced substances.

The shift towards renewable energy is one of the main challenges of this generation. Dye-sensitized solar cells (DSSC), based on donor-acceptor architectures, can help on this transition as they present excellent photovoltaic efficiencies yet cheap and simple manufacturing. For molecular heterojunctions DSSCs, donor-acceptor pairs are linked in a covalent manner, which facilitates their tailoring and rational design. Nevertheless, reliable computational characterization of charge transfer rate constants (kCT) is needed to speed this development process up. In this context, the performance of time-dependent density functional theory for the calculation of kCT's in donor-acceptor fullerene-based dyads has not been benchmarked yet. Herein, we present a detailed analysis on the performance of seven well-known density functional approximations (DFAs) for this type of systems, focusing on several parameters as the reorganization energies (λ), electronic couplings (VDA), and Gibbs energies (ΔG^0_CT), as well as in the final rate constants. The amount of exact exchange at short range (SR) and long range (LR) electron-electron distances (and the transition from SR to LR) turned out to be key for the success of the prediction. The tuning of these parameters improves significantly the performance of current DFAs ; This work was supported with funds from the Ministerio de Economía y Competitividad (MINECO) of Spain (project CTQ2017- 85341-P to M.S. and A.A.V.), the Spanish government MICINN (project PGC2018-098212-B-C22 to J.M.L), and the Generalitat de Catalunya (project 2017SGR39 to M.S. and J.M.L.). We thank the Spanish government for the predoctoral grant to P.B.-S. (FPU17/02058)

Near infrared photodetectors are a widespread and fundamental technology in many disciplines, from astronomy and telecommunications to medical sciences. Current technologies are now striving to include new aspects in this technology such as wearability, flexibility and tunability. Organic photodetectors easily offer many of those advantages but their relatively high bandgaps hinder NIR operation. In this work, we demonstrate solution processed organic photodetectors with improved NIR response thanks to a nanostructured active layer in the shape of a photonic crystal. The latter strongly increases the charge transfer state absorption, which is normally weak but broadband, increasing the optical path of light and resulting in remarkable photoresponse significantly below the band gap of the blend. We show responsivities up to 50 mA W−1 at 900 nm for PBTTT:PC71BM based photodetectors. On top of that, by varying the lattice parameter of the photonic crystal structure, the spectral response of the photodetectors can be tuned beyond 1000 nm. Furthermore, our photonic structure can be easily implemented in the device in a single nanoimprinting step, with minimal disruption on the fabrication process, which makes this approach very promising for upscaling. ; We greatly acknowledge financial support from the Ministerio de Ciencia, Innovación y Universidades MICINN with projects PGC2018-095411-B-I00, MAT2016-79053-P and MAT2015-70850-P and the "Severo Ochoa" excellence program SEV-2015-0496; Generalitat de Catalunya program AGAUR 2017-SGR-00488; and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grants no. CoG648901 and StG637116). P. M. acknowledges financial support from an FPI contract (2017) of the MICINN (Spain) cofounded by the ESF. M. G. R. acknowledges financial support from an FPU grant (no. 16/02631) (2017) of the MICINN (Spain). M. G. R. and P. M. B. acknowledge the departments of Physics, Chemistry and Geology of the Autonomous University of Barcelona (UAB) as coordinators of the PhD programme in Materials Science. We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

Fe-doped Bi12MnO20–BiMn2O5 ceramics was sintered at 1130 K for 6 h in ambient air. Two centro-symmetric phases formed thermodynamically stable self-composite material that was deduced from X-ray pattern analysis. The lattice parameters were a = 10.147(8) Å—for the cubic I23 Bi12MnO20 phase; and a = 7.545(4) Å, b = 8.538(1) Å, c = 5.758(3) Å—for the orthorhombic Pbam BiMn2O5 phase. The 57Fe Mössbauer spectrum, recorded at room temperature, has shown pure electronic quadrupolar split. The major doublets reflected the occurrence of Fe3+ ions distributed in two sites, i.e., octahedral Fe4+O6 and square pyramidal Fe3+O5, with preferential occupation of the pyramidal sites, that was consistent with the Pbam phase symmetry. The third doublet resulted from the presence of iron Fe3+ in tetrahedral Fe3+O4 coordination and corresponded to a small admixture of the I23 phase. The DC resistivity ρDC(T) dependence on temperature has shown thermally activated features, and the value of Ea,DC varied in the range of 0.22–0.37 eV. The electric impedance was measured in the f = 20 Hz–1 MHz and 100–690 K range. Two electrical relaxations were determined using the electric modulus formalism M″(T). Low-temperature relaxation has shown the temperature-dependent activation energy EA,1 = 0.14–0.20 eV and characteristic time values of τ01 = 10−10–10−12 s in 100–200 K range. It was attributed to the charge transfer between Mn4+/Mn3+ sites. The other relaxation occurred in the 170–220 K range, and it exhibited the following values: τ02 = 10−11 s, and EA,2 = 0.27 eV. A disorder-related VRH polaron model was proposed for ρDC(T) and for electric relaxation processes. ; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

We present the non-adiabatic, conical-intersection quantum dynamics of the title collision where reactants and products are in the ground electronic states. Initial-state-resolved reaction probabilities, total integral cross sections, and rate constants of two H 2 vibrational states, v 0 = 0 and 1, in the ground rotational state (j 0 = 0) are obtained at collision energies E coll ≤ 3 eV. We employ the lowest two excited diabatic electronic states of HeH2+ and their electronic coupling, a coupled-channel time-dependent real wavepacket method, and a flux analysis. Both probabilities and cross sections present a few groups of resonances at low E coll , whose amplitudes decrease with the energy, due to an ion-induced dipole interaction in the entrance channel. At higher E coll , reaction probabilities and cross sections increase monotonically up to 3 eV, remaining however quite small. When H 2 is in the v 0 = 1 state, the reactivity increases by ~2 orders of magnitude at the lowest energies and by ~1 order at the highest ones. Initial-state resolved rate constants at room temperature are equal to 1.74 × 10 -14 and to 1.98 × 10 -12 cm 3 s -1 at v 0 = 0 and 1, respectively. Test calculations for H 2 at j 0 = 1 show that the probabilities can be enhanced by a factor of ~1/3, that is ortho-H 2 seems ~4 times more reactive than para-H 2 ; The research leading to these result has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement n. 610256 (NANOCOSMOS), the HPC Europa3 Project (INFRAIA-2013- 1-730897) with the support of the EC Research Innovation Action under H2020 Programme and the COST Action CM1401 (Our Astrochemical History). Also, we acknowledge support by the Ministerio de Economía y Competitividad under grants No. FIS2014-52172-C2-2-P and FIS2017-83473-C2-2-P. CINECA is also acknowledged for computer time awarded via the ISCRA programme

Tuning the Fermi level (EF) in two-dimensional transition metal dichalcogenide (TMDC) semiconductors is crucial for optimizing their application in (opto-)electronic devices. Doping by molecular electron acceptors and donors has been suggested as a promising method to achieve EF-adjustment. Here, we demonstrate that the charge transfer (CT) mechanism between TMDC and molecular dopant depends critically on the electrical nature of the substrate as well as its electronic coupling with the TMDC. Using angle-resolved ultraviolet and X-ray photoelectron spectroscopy, we reveal three fundamentally different, substrate-dependent CT mechanisms between the molecular electron acceptor 1,3,4,5,7,8-hexafluoro-tetracyano-naphthoquinodimethane (F6TCNNQ) and a MoS2 monolayer. Our results demonstrate that any substrate that acts as charge reservoir for dopant molecules can prohibit factual doping of a TMDC monolayer. On the other hand, the three different CT mechanisms can be exploited for the design of advanced heterostructures, exhibiting tailored electronic properties in (opto-)electronic devices based on two-dimensional semiconductors. ; This work was funded by the Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 182087777 - SFB 951. S.P. acknowledges support by the Alexander von Humboldt-Stiftung. V.T. acknowledges the support from KAUST Solar Center Seed fund and under User Proposals (#4420 and #5067) at the Molecular Foundry, Lawrence Berkeley National Lab, supported by the Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. This work was supported by the KIST Institutional Program (Project No. 2E29850) and the National Research Foundation (NRF) of Korea under Grant 2018M3D1A1058793, funded by the Korean Government. Part of Fig. 4 was created with the software VESTA (Momma, K. and Izumi, F. VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 44, 1272–1276 (2011)).