Neutral and Anion Species of Quinoidal Thienothiophene Diketopyrrolopyrroles Display a Common Aggregation Mode.

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.

Aggregation of One-Dimensional Wires: The Case of Long Oligoynes.

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 p-conjugated oligoyne chains is rare, given the minimal p-p intermolecular interactions of the weakly polarizable polyyne chain, 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 140-180 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.

Identification and management of tomato brown rugose fruit virus in greenhouses in Mexico.

Tomato brown rugose fruit virus (ToBRFV) has become a cause of great concern in the global tomato agro-industry since its first report in Israel in 2014. Global tomato production is affected by ToBRFV, and management practices are being evaluated. We tested seed lots from international producers as well as greenhouse substrates and water wells as possible sources of virus contamination. We identified a second introduction of ToBRFV in Mexico by a strain closely resembling isolates from the Netherlands and the Middle East. ToBRFV was detected by RT-PCR in seed coats and epicotyls (from commercial seeds and seedlings obtained from infected tomato plants), indicating a transmission rate of 9%. Virus-like particles (VLPs) were found in wells used for irrigation in greenhouses, but these exhibited low infectivity. These findings suggest that water sources could serve as ToBRFV reservoirs. We evaluated four chemical and six thermal methods for sanitizing substrates, plasticware, and other greenhouse utensils, using detached leaf bioassays in Nicotiana rugosa. The most effective chemical sanitization method was treatment with glutaraldehyde plus quaternary ammonium salts and pentapotassium salts. The most effective heat treatment was at 92°C for 30 minutes, which inactivated the virus. Tomato producers could implement these sanitization methods to control ToBRFV.

Nonadiabatic Vibrational Resonance Raman Spectra from Quantum Dynamics Propagations with LVC Models. Application to Thymine.

We present a viable protocol to compute vibrational resonance Raman (vRR) spectra for systems with several close-lying and potentially coupled electronic states. It is based on the parametrization of linear vibronic coupling (LVC) models from time-dependent density functional theory (TD-DFT) calculations and quantum dynamics propagations of vibronic wavepackets with the multilayer version of the multiconfiguration time-dependent Hartree (ML-MCTDH) method. Our approach is applied to thymine considering seven coupled electronic states, comprising the three lowest bright states, and all vibrational coordinates. Computed vRR at different excitation wavelengths are in good agreement with the available experimental data. Up to 250 nm the signal is dominated by the lowest HOMO → LUMO transition, whereas at 233 nm, in the valley between the two lowest energy absorption bands, the contributions of all the three bright states, and their interferences and couplings, are important. Inclusion of solvent (water) effects improves the agreement with experiment, reproducing the coalescence of vibrational bands due to CC and C═O stretchings. With our approach we disentangle and assess the effect of interferences between the contribution of different quasi-resonant states to the transition polarizability and the effect of interstate couplings. Our findings strongly suggest that in cases of close-lying and potentially coupled states a simple inclusion of interference effects is not sufficient, and a fully nonadiabatic computation should instead be performed. We also document that for systems with strong couplings and quasi-degenerate states, the use of HT perturbative approach, not designed for these cases, may lead to large artifacts.

Chirality Amplified: Long, Discrete Helicene Nanoribbons.

Here we report the synthesis of two polyhelicene frameworks consisting, from end-to-end, of 18 and 24 fused benzene rings. The latter exhibits the largest electronic circular dichroism in the visible spectrum of any molecule. These shape-persistent helical nanoribbons incorporate multiple helicenes, a class of contorted polycyclic aromatic molecules consisting of ortho-annulated rings. These conjugated, chiral molecules have interesting chemical, biological, and chiroptical properties; however, there are very few helicenes with extraordinary chiroptical response over a broad range of the visible spectrum-a key criterion for applications such as chiral optoelectronics. In this report, we show that coupling the polyhelicene framework with multiple perylene-diimide subunits elicits a significant chiroptic response. Notably, the molar circular dichroism increases faster than the absorptivity of these molecules as their helical axis lengthens. Computational analysis reveals that the greatly amplified circular dichroism arises from exciton-like interactions between the perylene-diimide and the helicene moieties. We predict that even greater chiroptic enhancement will result from further axial elongation of these nanoribbons, which can be readily enabled via the iterative synthetic method presented herein.

Duplications and Functional Convergence of Intestinal Carbohydrate-Digesting Enzymes.

Vertebrate diets and digestive physiologies vary tremendously. Although the contribution of ecological and behavioral features to such diversity is well documented, the roles and identities of individual intestinal enzymes shaping digestive traits remain largely unexplored. Here, we show that the sucrase-isomaltase (SI)/maltase-glucoamylase (MGAM) dual enzyme system long assumed to be the conserved disaccharide and starch digestion framework in all vertebrates is absent in many lineages. Our analyses indicate that independent duplications of an ancestral SI gave rise to the mammalian-specific MGAM, as well as to other duplicates in fish and birds. Strikingly, the duplicated avian enzyme exhibits similar activities to MGAM, revealing an unexpected case of functional convergence. Our results highlight digestive enzyme variation as a key uncharacterized component of dietary diversity in vertebrates.

A computational study of the vibronic effects on the electronic spectra and the photophysics of aza[7]helicene.

We report a computational study on vibronic effects in the spectroscopy, photoinduced processes and decay back to the ground state of aza[7]helicene, a helicene with an unusually high fluorescence quantum yield (QY = 0.39). In a first step, we compute and assign the absorption and electronic circular dichroism (ECD) spectra in its full frequency range from 2.7 to 5.0 eV, accounting for nonadiabatic effects. Then we compute the quantum dynamics of the cascade of ultrafast internal conversions of the highly-excited singlet states to the lowest-energy one S1. Finally we adopt Fermi golden rule rates to compute the QY of the dye, taking into account the competition between the radiative decay and the nonradiative decays to the ground state and to the energy-accessible triplet states. We use time-dependent density functional theory (TD-DFT), including solvent (dichloromethane) effects within the polarizable continuum model, to parameterize a linear vibronic coupling (LVC) model involving the first lowest 12 singlet states and all the normal coordinates. Nonadiabatic spectra and internal conversions dynamics are then computed through wavepacket propagations with the Multilayer (ML) extension of the Multiconfigurational Time Dependent Hartree method (ML-MCTDH). We highlight the molecular vibrations playing a major role in determining the shape of the spectra and analyse the effect of inter-state couplings. At the same time we report a breakdown of perturbative Herzberg-Teller approach. The computed QY is in perfect agreement with experiment and allows us to ascertain that intersystem crossings are the processes limiting the fluorescence from S1. They involve the three lowest triplet states and are made effective by spin-orbit coupling and vibronic effects.

Parameterization of a linear vibronic coupling model with multiconfigurational electronic structure methods to study the quantum dynamics of photoexcited pyrene.

With this work, we present a protocol for the parameterization of a Linear Vibronic Coupling (LVC) Hamiltonian for quantum dynamics using highly accurate multiconfigurational electronic structure methods such as RASPT2/RASSCF, combined with a maximum-overlap diabatization technique. Our approach is fully portable and can be applied to many medium-size rigid molecules whose excited state dynamics requires a quantum description. We present our model and discuss the details of the electronic structure calculations needed for the parameterization, analyzing critical situations that could arise in the case of strongly interacting excited states. The protocol was applied to the simulation of the excited state dynamics of the pyrene molecule, starting from either the first or the second bright state (S2 or S5). The LVC model was benchmarked against state-of-the-art quantum mechanical calculations with optimizations and energy scans and turned out to be very accurate. The dynamics simulations, performed including all active normal coordinates with the multilayer multiconfigurational time-dependent Hartree method, show good agreement with the available experimental data, endorsing prediction of the excited state mechanism, especially for S5, whose ultrafast deactivation mechanism was not yet clearly understood.

Nonadiabatic Absorption Spectra and Ultrafast Dynamics of DNA and RNA Photoexcited Nucleobases.

We have recently proposed a protocol for Quantum Dynamics (QD) calculations, which is based on a parameterisation of Linear Vibronic Coupling (LVC) Hamiltonians with Time Dependent (TD) Density Functional Theory (TD-DFT), and exploits the latest developments in multiconfigurational TD-Hartree methods for an effective wave packet propagation. In this contribution we explore the potentialities of this approach to compute nonadiabatic vibronic spectra and ultrafast dynamics, by applying it to the five nucleobases present in DNA and RNA. For all of them we computed the absorption spectra and the dynamics of ultrafast internal conversion (100 fs timescale), fully coupling the first 2-3 bright states and all the close by dark states, for a total of 6-9 states, and including all the normal coordinates. We adopted two different functionals, CAM-B3LYP and PBE0, and tested the effect of the basis set. Computed spectra are in good agreement with the available experimental data, remarkably improving over pure electronic computations, but also with respect to vibronic spectra obtained neglecting inter-state couplings. Our QD simulations indicate an effective population transfer from the lowest energy bright excited states to the close-lying dark excited states for uracil, thymine and adenine. Dynamics from higher-energy states show an ultrafast depopulation toward the more stable ones. The proposed protocol is sufficiently general and automatic to promise to become useful for widespread applications.

Distinct Helical Molecular Orbitals through Conformational Lock*.

Several theoretical studies have proposed strategies to generate helical molecular orbitals (Hel-MOs) in [n]cumulenes and oligoynes. While chiral even-[n] cumulenes feature Hel-MOs, odd-[n] cumulenes may also present them if the terminal groups lie in different planes. However, the proposed systems have been either experimentally unfeasible or resulted in opposite pseudo-degenerated Hel-MOs. We hereby demonstrate the introduction of a remarkable energy difference between helical orbitals of opposite twist by fixing the torsion angle between the terminal groups in butadiyne fragments. To experimentally lock the conformation of the terminal groups, we designed and synthesized cyclic architectures by combining acetylenes with chiral spirobifluorenes. The high stability of these systems with distinct helical orbitals allowed their isolation and full characterization. In our view, these results constitute a step further in the development of real systems presenting helical molecular orbitals.

The role of chlorine position in the electronic circular dichroism of chlorophenyl-ethanol investigated by vibronic calculations.

(R)-1-phenyl-ethanol (PhEtOH) and the different isomers of (R)-1-(chlorophenyl)ethanol (ClPhEtOH) exhibit very interesting electronic circular dichroism (ECD) in methanol. In all cases, the spectrum shows clear vibronic features, but it is monosignated and negative for PhEtOH and meta-ClPhEtOH, positive for the ortho isomer and bisignated for the para isomer. We used computational chemistry to rationalise this behaviour adopting CAM-B3LYP/def2-TZVP, describing the bulk solvent effects with polarizable continuum models and solute-solvent specific interactions with clusters comprising the solute and two solvent molecules. We adopted harmonic vibronic models to compute the ECD spectral shapes of all stable conformers, and we obtained the room-temperature spectra by Boltzmann average. Simulated spectra are in very good agreement with experiment and allow us to rationalise their difference in terms of the relevance of Franck-Condon (FC) and Herzberg-Teller (HT) intensity-borrowing contributions, modulated by the substituent effect. The bisignated shape of the spectrum of para-ClPhEtOH arises from the competition of opposite-sign FC and HT bands, promoted by different vibrational modes. Due to the challenges we document in computing its ECD spectrum, para-ClPhEtOH represents a good test case to help the development of novel methodologies for an improved description of weak vibronic ECD spectra of flexible systems in explicit solvents.

A computational study of the vibrationally-resolved electronic circular dichroism spectra of single-chain transoid and cisoid oligothiophenes in chiral conformations.

We simulate the vibronic profile of the electronic circular dichroism (ECD) spectra of oligothiophenes in cisoid and transoid chiral arrangements. We consider oligomers of different lengths, from two to fifteen units, and investigate extensively how the ECD spectral shapes depend on the inter-ring torsions. In general, the molecular structures we consider are not stationary points of the ground state potential energy surface. Therefore, in order to perform vibronic calculations, we present a new computational protocol able to define reduced-dimensionality models where the effect of the off-equilibrium modes is removed. This is done adopting a description of the vibrational motions in curvilinear internal coordinates, and vertical harmonic models coupled with an iterative application of projectors to define energy Hessians, and therefore effective normal modes, in the space complementary to the one of the off-equilibrium coordinates. Although we consider both Franck-Condon and Herzberg-Teller contributions, the results show that transoid twisted ribbons always give rise to monosignated ECD spectra, while bi-signated and multi-signated spectra are expected for cisoid helices. These findings are explained on the basis of the different transition strengths of the lowest electronic states imparted by the different spatial arrangement, that is almost linear for transoid structures and more globular for cisoid ones. We predicted the chiroptical response of a large number of possible molecular arrangements. These data are employed to critically discuss the experimental ECD of polythiophenes in different experimental conditions, forming either aggregates or host-guest complexes. The method here proposed to perform vibronic calculations in reduced-dimensionality models is of general applicability and its potential interest goes beyond the practical application presented here.

Charge transfer at the nanoscale and the role of the out-of-plane vibrations in the selection rules of surface-enhanced Raman scattering.

Surface-enhanced Raman scattering (SERS) spectroscopy of pyridazine shows the selective enhancement of the bands recorded at about 1570, 1450 and 380 cm-1, which are assigned to two different types of vibrations. The first two correspond to in-plane 8a;νring and 19b;δ(CH) totally symmetric A1 modes, respectively, while the last band is assigned to the out-of-plane 16b;τring,B1 vibration. The selective enhancement has been analyzed on the basis of a resonant Raman process involving photoexcited metal (M)-to-molecule (A) charge transfer (CT: M-A + hν → M+-A-) states of the metal-adsorbate surface complex, which have also been related to the doublet electronic states of the corresponding radical anion of the adsorbate (A-). According to the selection rules of the electromagnetic/plasmonic SERS enhancement mechanism, the simultaneous enhancement of in-plane and out-of-plane modes could be attributed to different orientations of the adsorbate (perpendicular and parallel, respectively, or tilted) with respect to the metallic surface. The calculated resonance Raman-CT spectra (SERS-CT) and the vibrational wavenumbers of isolated pyridazine and of the pyridazine-Ag2 complex obtained from electronic structure calculations suggest a single type of molecule adsorbed with perpendicular orientation. The relative SERS enhancements of both in-plane and out-of-plane modes are due to Franck-Condon factors related to differences between the equilibrium geometries (A1 vibrations, ΔQ ≠ 0) and gradients (B1 vibrations, Δν ≠ 0 and ΔQ ≠ 0), respectively, of the potential energy surfaces of the involved ground and photoinduced CT electronic states. Therefore, the selective enhancement of the SERS bands of pyridazine is controlled by a general metal-to-molecule resonant CT mechanism. This conclusion supports the usefulness of SERS in studying the subtle electronic structure of charged interfaces as well as key processes such as electron transfer at the nanoscale.

An MS-CASPT2 study of the photodecomposition of 4-methoxyphenyl azide: role of internal conversion and intersystem crossing.

The photochemical decomposition of 4-methoxyphenyl azide (CH3O-Ph-N3) is investigated using multiconfigurational second-order perturbation theory (MS-CASPT2). In addition, the multi-state resonance Raman spectra of the reactant, intermediates, and product are computed with a multi-state version of the vibronic theory of Albrecht. The results support that the key step of the photolysis of the parent azide is a 21A'/23A'' intersystem crossing which in a second step decays through a 23A''/13A'' conical intersection to give directly the formation of triplet 4-methoxyphenyl nitrene (CH3O-Ph-N) in its lowest electronic state, 13A''. It is found that the efficiency of the cited intersystem crossing is enhanced by the close presence of a 21A'/21A'' conical intersection. On the other hand, the calculated spectra suggest that the only two species which would be observed in the gas phase experiments are the triplet nitrene plus 4,4'-dimethoxyazobenzene.

Toward a general mixed quantum/classical method for the calculation of the vibronic ECD of a flexible dye molecule with different stable conformers: Revisiting the case of 2,2,2-trifluoro-anthrylethanol.

We extend a recently proposed mixed quantum/classical method for computing the vibronic electronic circular dichroism (ECD) spectrum of molecules with different conformers, to cases where more than one hindered rotation is present. The method generalizes the standard procedure, based on the simple Boltzmann average of the vibronic spectra of the stable conformers, and includes the contribution of structures that sample all the accessible conformational space. It is applied to the simulation of the ECD spectrum of (S)-2,2,2-trifluoroanthrylethanol, a molecule with easily interconvertible conformers, whose spectrum exhibits a pattern of alternating positive and negative vibronic peaks. Results are in very good agreement with experiment and show that spectra averaged over all the sampled conformational space can deviate significantly from the simple average of the contributions of the stable conformers. The present mixed quantum/classical method is able to capture the effect of the nonlinear dependence of the rotatory strength on the molecular structure and of the anharmonic couplings among the modes responsible for molecular flexibility. Despite its computational cost, the procedure is still affordable and promises to be useful in all cases where the ECD shape arises from a subtle balance between vibronic effects and conformational variety.

An approach to the electronic structure of molecular junctions with metal clusters of atomic thickness.

TD-DFT calculations predict a linear dependence of the energies of charge transfer states of Agn-pyrazine-Agn molecular junctions on the inverse of the size (1/n) of the linear metal chains. The density of charge (qeff = q/n) in the metal-to-metal charge transfer excited states (CTMM: Agnq-pyrazine-Agn-q) smoothly tunes the electronic structure of the junction, especially the metal-to-molecule charge transfer states (CT0 and CT1) and the first excited singlet of pyrazine (S1,Pz). In enlarged junctions, pyrazine bonds preferably to one of the Agn clusters and this weak adsorption produces a significant unexpected asymmetry for forward and reverse charge transfer processes.

Linear Vibronic Coupling Approach for Surface-Enhanced Raman Scattering: Quantifying the Charge-Transfer Enhancement Mechanism.

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 E⃗ 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 E⃗ through a fragment-based maximum-overlap diabatization. By presenting results at different values of E⃗, 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.

Time-Resolved X-ray Absorption Spectroscopy: An MCTDH Quantum Dynamics Protocol.

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.

A dataset about Spanish young people's digital skills, use of technology and online platforms.

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.