Electron Propagator Theory Approach to the Electron Binding Energies of a Prototypical Photo-Switch Molecular System: Azobenzene

Low-Energy Electron Scattering from Pyrrole and Its Isomers

Low-energy electron scattering from pyrrole and its isomers, such as 2-H pyrrole, cyclopropanecarbonitrile, and Z-2 butenenitrile, is explored in detail in this article. The electron interaction with the target molecules was studied through R-matrix theory. We have used minimal STO-3G and advanced DZP basis sets on a fine energy grid from 0.1 to 12 eV electron energy in the calculation. The properties of the STO-3G and DZP-based targets, such as their ionization energy, polarizability, dipole moment, rotational constant, principal moment of inertia, ground-state energy, and orbital energies, were investigated and compared to previously reported data. The elastic and inelastic channels showed the appearance of shape and Feshbach resonances for pyrrole and its isomers. The ultralow-energy region resonance was observed for Z-2 butenenitrile at 0.47 eV. With STO-3G and DZP basis sets, we estimated elastic, excitation, and momentum-transfer cross sections. The differential cross section for the present polar molecules was studied at 5 eV. The dissociative electron attachment channel for pyrrole and its isomers was studied for the pyrrolide anion. The data presented here will be helpful in astrophysical, astrochemical, atmospheric, and low-energy plasma modeling due to the presence of pyrrole and its isomers and the pyrrolide anion in the celestial bodies. The estimated data are also helpful in the biomedical field, radiation therapy, and pharmaceuticals.

Dissociative electron attachment to gold(I)-based compounds: 4,5-dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I)

With the use of proton-NMR and powder XRD (XRPD) studies, the suitability of specific Au-focused electron beam induced deposition (FEBID) precursors has been investigated with low electron energy, structure, excited states and resonances, structural crystal modifications, flexibility, and vaporization level. 4,5-Dichloro-1,3-diethyl-imidazolylidene trifluoromethyl gold(I) is a compound that is a uniquely designed precursor to meet the needs of focused electron beam-induced deposition at the nanostructure level, which proves its capability in creating high purity structures, and its growing importance in other AuIm_x and AuCl_nB (where x and n are the number of radicals, B = CH, CH₃, or Br) compounds in the radiation cancer therapy increases the efforts to design more suitable bonds in processes of SEM (scanning electron microscopy) deposition and in gas-phase studies. The investigation performed of its powder shape using the XRPD XPERT³ panalytical diffractometer based on CoK_α lines shows changes to its structure with change in temperature, level of vacuum, and light; the sensitivity of this compound makes it highly interesting in particular to the radiation research. Used in FEBID, though its smaller number of C, H, and O atoms has lower levels of C contamination in the structures and on the surface, it replaces these bonds with C-Cl and C-N bonds that have lower bond-breaking energy. However, it still needs an extra purification step in the deposition process, either H₂O, O₂, or H jets.

Photoswitching/back-switching assessment of biobased cellulose acetate/azobenzene handleable films under visible-light LED irradiation

The light-induced processes performed by photofunctional polymer films are crucial aspects of developing integrated energy storage devices properly. Herein, we report the preparation, characterization, and study of the optical properties of a series of biobased cellulose acetate/azobenzene (CA/Az1) handleable films at different compositions. The photoswitching/back-switching behavior of the samples was investigated using varied LED irradiation sources. Additionally, poly(ethylene glycol) (PEG) was deposited onto cellulose acetate/azobenzene films to study the back-switching process's effect and nature in the fabricated films. Interestingly, the melting enthalpies of PEG before and after being irradiated with blue LED light were 2.5 mJ and 0.8 mJ, respectively. Conveniently, FTIR and UV-visible spectroscopy, thermogravimetry (TGA), contact angle, differential scanning calorimetry (DSC), polarized light microscopy (PLM), and atomic force microscopy (AFM) were used for the characterization of the sample films. Complementarily, theoretical electronic calculations provided a consistent approach to the energetic change in the dihedral angles and non-covalent interaction for the trans and cis isomer in the presence of cellulose acetate monomer. The results of this study revealed that CA/Az1 films are viable photoactive materials displaying handleability attributes with potential uses in harvesting, converting, and storing light energy.

Oriented External Electric Field Tuning of Unsubstituted Azoheteroarene Thermal Isomerization Half-Lives

Azoheteroarenes are relatively new photoswitchable compounds, where one of the phenyl rings of an azobenzene molecule is replaced by a heteroaromatic five-membered ring. Recent findings on methylated azoheteroarenes show that these photoswitches have potential in various optically addressable applications. The thermal stability of molecular switches is one of the primary factors considered in the design process. For molecular memory or energy storage devices, long thermal relaxation times are required. However, inducing a short thermal isomerization lifetime is required to release stored energy or as an alternative to photoswitching to avoid overlapping absorption spectra that reduce switching fidelity. In this study, we investigate how oriented external electric fields can be used to tune the thermal isomerization properties of three unsubstituted heteroaryl azo compounds-azoimidazole, azopyrazole, and azopyrrole. We show that favorable electric field orientations can increase the thermal half-life of studied molecules by as much as 60 times or reduce it from tens of days to seconds, compared to their half-life values in the field-free environment. A deeper understanding of the relationship between structure and kinetic properties provides insight as to how molecular switches can be designed for their electric field response in switching applications.

Ultrafast Nonadiabatic Photoisomerization Dynamics Mechanism for the UV Photoprotection of Stilbenoids in Grape Skin

Natural UV photoprotection plays a vital role in physiological protection. It has been reported that UVC radiation can make resveratrol (RSV) and piceatannol (PIC) accumulate in grape skin. In this work, we demonstrated that RSV and PIC could significantly absorb UVA and UVB, and confirmed their satisfactory photostability. Furthermore, we clarified the UV photoprotection mechanism of typical stilbenoids of RSV and PIC for the first time by using combined femtosecond transient absorption (FTA) spectroscopy and time-dependent density functional theory (TD-DFT) calculations. RSV and PIC can be photoexcited to the excited state after UVA and UVB absorption. Subsequently, the photoisomerized RSV and PIC quickly relax to the ground state via nonadiabatic transition from the S₁ state at a conical intersection (CI) position between potential energy surfaces (PESs) of S₁ and S₀ states. This ultrafast trans-cis photoisomerization will take place within a few tens of picoseconds. As a result, the UV energy absorbed by RSV and PIC could be dissipated by an ultrafast nonadiabatic photoisomerization process.

Asymmetric Density Fitting with Modified Cholesky Decomposition Applied to Second-Order Electron Propagator

Computation of molecular orbital electron repulsion integrals (MO-ERIs) as a transformation from atomic orbital ERIs (AO-ERIs) is the bottleneck of second-order electron propagator calculations when a single orbital is studied. In this contribution, asymmetric density fitting is combined with modified Cholesky decomposition to generate efficiently the required MO-ERIs. The key point of the presented algorithms is to keep track of integrals through partial contractions performed on three-center AO-ERIs; these contractions are stored in RAM instead of the AO-ERIs. Two implementations are provided, an in-core, which reduces the arithmetic and memory scaling factors as compared to the four-center AO-ERIs contraction method, and a semidirect, which overcomes memory limitations by evaluating antisymmetrized MO-ERIs in batches. On the numerical side, the proposed approach is fast and stable. The bad effects due to ill conditioning, namely, several negative and close to zero eigenvalues due to machine round off errors of the matrix associated with the density fitting process, are effectively controlled by means of a modified Cholesky factorization that avoids the matrix inversion needed to perform the asymmetrical density fitting implementation. The numerical experience presented shows that the in-core implementation is highly competitive to perform calculations on medium and large basis sets, while the semidirect implementation has small variations in time by changes in the available memory. The general applicability is illustrated on a set of selected relatively large-size molecules.