ABSTRACT
Electrochemical SERS of pyridine adsorbed on a silver electrode has been analyzed by comparing the spectra to the calculated normal Raman and resonance Raman intensities of model systems of pyridine bonded to linear silver clusters with different densities of charge through the nitrogen (Ag-NPy) or flipped through the hydrogen in the para-position (Ag-HPy). The changes observed in the ν(CH) region of the SERS have been investigated for the first time and related to a molecular reorientation at negative surface excess of charge of the metal in such a way that the ν(CH) bands with the highest (mode 2) and lowest (mode 13) wavenumber dominate this spectral region at positive or negative electrode potentials, respectively. The calculations support that the ν(CH) region is dominated by a specific vibration depending on pyridine orientation and suggest that both species coexist in the SERS recorded at negative potentials. This conclusion is supported by the SERS of centrosymmetric pyrazine which do not show this behavior and remembers the predictions from the old propensity rules of the so-called electromagnetic mechanism of SERS.
ABSTRACT
A comprehensive investigation of two new molecular triads incorporating the diketopyrrolopyrrole unit into a quinoidized thienothiophene skeleton, which is further end-capped with dicyanomethylene (DPP-TT-CN) or phenoxyl groups (DPP-TT-PhO), has been carried out. A combination of UV-Vis-NIR and infrared spectroelectrochemical techniques and cryogenic UV-Vis-NIR absorption spectroscopy supported by theoretical calculations has been used. The main result is the formation of similar H-aggregates in the dimerization process of the neutral molecules and of the charged anionic species. The experimental absorption spectra of the aggregated species are accurately reproduced by quantum chemical calculations using the Spano's model, including excitonic coupling for the dimeric forms and full vibronic resolution of the absorption bands. The strong excitonic coupling taking place is key to understand the electronic structure of the dimeric aggregates and has been instrumental to disentangle the type of H-aggregation. This study is of relevance to get a better understanding of the molecular aggregation of organic p-conjugated chromophores and is useful as a guideline for the refinement of the engineering of molecular materials for which supramolecular design is required.
ABSTRACT
We show an unexpected aggregation phenomenon of a long oligoyne (Py[16]) with 16 contiguous triple bonds and endcapped with bulky 3,5-bi(3,5-bis-tert-butylphenyl)pyridine groups. Aggregation of 1D π-conjugated oligoyne chains is rare given the minimal π-π intermolecular interactions as well as its flexibility that works against self-assembly. In dilute solutions, the reversible aggregation of Py[16] initiates at low temperature in the range of 140-180â K, and is not observed for shorter oligoynes in this series. Cryogenic UV/Vis electronic absorption spectra and vibrational Raman spectra with different laser wavelength lines tuning from in-resonance to off-resonance conditions have been used to extract the vibrational features characterizing the monomer and aggregate species. Theoretical calculations complement the spectroscopic findings.
ABSTRACT
The outstanding amplification observed in surface-enhanced Raman scattering (SERS) is due to several enhancement mechanisms, and standing out among them are the plasmonic (PL) and charge-transfer (CT) mechanisms. The theoretical estimation of the enhancement factors of the CT mechanism is challenging because the excited-state coupling between bright plasmons and dark CT states must be properly introduced into the model to obtain reliable intensities. In this work, we aim at simulating electrochemical SERS spectra, considering models of pyridine on silver clusters subjected to an external electric field Eâ that represents the effect of an electrode potential Vel. The method adopts quantum dynamical propagations of nuclear wavepackets on the coupled PL and CT states described with linear vibronic coupling models parametrized for each Eâ through a fragment-based maximum-overlap diabatization. By presenting results at different values of Eâ, we show that indeed there is a relation between the population transferred to the CT states and the total scattered intensity. The tuning and detuning processes of the CT states with the bright PLs as a function of the electric field are in good agreement with those observed in experiments. Finally, our estimations for the CT enhancement factors predict values in the order of 105 to 106, meaning that when the CT and PL states are both in resonance with the excitation wavelength, the CT and PL enhancements are comparable, and vibrational bands whose intensity is amplified by different mechanisms can be observed together, in agreement with what was measured by typical experiments on silver electrodes.
ABSTRACT
Expressions for linear and nonlinear spectroscopy simulation in the X-ray window in which the time evolution of a photoexcited molecular system is treated via quantum dynamics are derived. By leveraging on the peculiar properties of core-excited/ionized states, first- and third-order response functions are recast in the limit of time-scale separation between the extremely short core-state lifetime and the (comparably longer) electronic-state transfer and nuclear vibrational motion. This work is a natural extension of Segatta et al. (J. Chem. Theory Comput. 2023, 19, 2075-2091), in which some of the present authors coupled MCTDH quantum dynamics to spectroscopy simulation at different levels of sophistication. Full quantum dynamics and approximate expressions are compared by simulating X-ray transient absorption spectroscopy at the carbon K-edge in the pyrene molecule.
ABSTRACT
Background: The datafication scenario of the current communicative ecosystem poses a challenge to media and digital literacy, especially in terms of participation and civic and democratic engagement of youth. Methods: For this purpose, through a survey with a representative sample of 600 young people in Spain, between 16 and 18 years old, we observed their level of digital literacy through three variables: technical competencies, informational competencies, and critical knowledge. This dataset also collects information on the reasons why young people use digital technology such as video games, consoles, computers or mobile phones. On the other hand, we also offer information on the types of social networks or applications and the time and types of uses by youngsters of different digital technologies and social media platforms. The survey includes socio-demographic factors such as gender including (male, female, and others). Conclusions: This survey offers researchers relevant data on the digital skills of Spanish youth and on the perceptions of the use of different digital technologies. This paper also reports the main descriptive data that can be expanded by researchers accessing the database.
Subject(s)
Communication , Digital Technology , Adolescent , Female , Humans , Male , Cell Phone , SpainABSTRACT
La hiperhidrosis o sudoración excesiva de las palmas de las manos, las axilas, la cara y las plantas de los pieses una afección que condiciona al paciente en su relaciónpsico-bio-social, dificultando sus relaciones sociales y sentimentales, así como en su aspecto laboral, por lo que surge la necesidad de un tratamiento efectivo con el fin de conseguir la disminución del sudor a niveles aceptables ola supresión del mismo.El objetivo de este trabajo es presentar nuestra experiencia en el tratamiento de la hiperhidrosis por videotoracoscopia.En este estudio fueron incluidos todos aquellos pacientes sometidos cirugía por hiperhidrosis desde enero del año 1999 hasta enero del 2009 por este equipo. Fueron realizadas 80 simpatectomías en 40 pacientes, resecandola cadena simpática desde T2 a T4, con un tiempo operatorio entre 15 y 50 minutos, siendo dadas de alta en promedio a las 24 hs, con mínima morbilidad.Los resultados para el paciente fueron óptimos, constatándose la desaparición de la sudoración ya en sala de operaciones.Considerando los resultados obtenidos en nuestros pacientes con el abordaje videotoracoscópico de la cadena simpática, esta es una técnica mínimamente invasiva,eficaz, segura, estéticamente aceptable y que lleva a una cura definitiva en casi el 100% de los casos.