Effects of TIPS-Functionalization and Perhalogenation on the Electronic, Optical, and Transport Properties of Angular and Compact Dibenzochrysene

Entropy-ruled nonequilibrium charge transport in thiazolothiazole-based molecular crystals: a quantum chemical study

The charge and energy fluctuations in molecular solids are crucial factors for a better understanding of charge transport (CT) in organic semiconductors. The energetic disorder-coupled molecular charge transport is still not well-established. Moreover, the conventional Einstein's diffusion (D)-mobility (μ) relation fails to explain the quantum features of organic semiconductors, including nonequilibrium and degenerate transport systems, where kB is the Boltzmann constant, T is the temperature and q is the electric charge. To overcome this issue, a unified version of the entropy-ruled D/μ relation was proposed by Navamani (J. Phys. Chem. Lett., 2024, 15, 2519-2528) for hopping and band transport systems as where d, η and heff are the dimension (d = 1, 2, 3), chemical potential and effective entropy, respectively. Within this context, we investigate the CT properties of 2,5-bis(4-methoxyphenyl)thiazolo[5,4-d]thiazole (MOP-TZTZ) and 2,5-bis(2,4,5 trifluorophenyl)-thiazolo[5,4-d]thiazole (TFP-TZTZ) molecular solids using electronic structure calculations and the entropy-ruled method. The CT key parameters such as charge transfer integral and site energy are computed by matrix elements of the Kohn-Sham Hamiltonian. Using Marcus theory, the charge transfer rate is numerically calculated for MOP-TZTZ and TFP-TZTZ molecular crystals under different site energy disorder (ΔEij(E⃑)) situations. Using our entropy-ruled method, the exact diffusion-mobility (D/μ) and other transport quantities such as thermodynamic density of states, conductivity, and current density are calculated for these derivatives at different applied electric field values via the site energy disorder. The theoretical results show that the molecule TFP-TZTZ has good hole mobility (∼0.012 cm2 V-1 s-1) at a site energy disorder value of 90 meV. The obtained ideality factor from the Navamani-Shockley diode current density equation categorizes the typical transport as either the Langevin-type or Shockley-Read-Hall mechanism in the studied molecular solids. Our analysis clearly shows that both the electron and hole transport in these MOP-TZTZ and TFP-TZTZ molecules follow the trap-free Langevin mechanism, which is indeed ideal for designing charge-transporting molecular devices.

First-Principles Investigation of the Optical Properties of Eumelanin Protomolecules

Using first-principles calculations, we investigate the absorption spectra (in the near-infrared, visible, and first UV range) of the two most probable eumelanin tetrameric molecules exhibiting either a linear open-chain or a cyclic porphyrine-like configuration. In order to simulate a realistic molecular system, an implicit solvent model is used in our calculations to mimic the effect of the solvated environment around the eumelanin molecule. Although the presence of solvent is found not to significantly affect the absorption pattern of both molecules, the onset of the spectra are shifted toward higher energies, especially for the linear tetramer. Interestingly, the absorption spectra and optical onsets of the two molecules differ significantly both in a vacuum and in ethanol. However, the two predicted spectra do not allow us to definitely discriminate between the two configurations when comparing the theoretical predictions with the available experimental spectrum. In addition, a mix of the two eumelanin configurations (close to fifty-fifty) leads to a maximum overlap between theoretical and experimental spectra. Consequently, this theoretical research shows that deeper insight can be gained using beyond DFT techniques on the real form of eumelanin protomolecules present in living systems as well as on their possible use in hybrid solar cells.

Discrimination of leucine and isoleucine via fragmentation by electromagnetic field

CONTEXT

We conduct comparative numerical studies of the effects of electric dipole field and electromagnetic radiation field on the amino acids leucine and isoleucine. Since they are structural isomers, distinguishing them by mass is a non-trivial task, while determination of protein structure can be crucial on many occasions. We emphasize the influence of the magnetic field of radiation by utilizing a modified basis sets with correction coefficients to the [Formula: see text] and [Formula: see text] orbitals following the Anisotropic Gaussian Type Orbitals method. Studying the electric potential of the isomers in dipole electric or electromagnetic fields proves that the different layout of leucine vs isoleucine is the main reason why some fragments could not be formed during chemical bond cleavage. Comparison of the chemical structure of the fragments created due to the decomposition of the isomers in the dipole electric or electromagnetic fields shows that their decomposition products are different. These findings can be used also for discrimination between the two isoleucine conformers, for which the cleavage starts at different values of the dipole electric field strength, as well as the products of the decomposition reaction are not identical. Our numerical calculations of the fragmentation outcomes, taking into account the magnetic field effects, can serve as a guidance for discrimination between the isomers/conformers.

METHODS

We applied the Becke's three-parameter hybrid functional approach with non-local correlation by Lee, Yang, and Parr ([Formula: see text]), together with the [Formula: see text] basis set as it is implemented in the GAUSSIAN09 quantum chemistry package in order to obtain the most stable conformers of leucine and isoleucine. We used the options provided by GAUSSIAN09 to add finite external field in order to perform the calculations of leucine and isoleucine in the electric dipole and electromagnetic fields. The Anisotropic Gaussian Type Orbitals method was used to obtain the correction coefficients which modify the original [Formula: see text] basis set in order to account for the effects of magnetic field of radiation. Results were visualized and the electrical potentials analyzed by the Molden visualization program.

Ab-initio and density functional theory (DFT) computational study of the effect of fluorine on the electronic, optical, thermodynamic, hole and electron transport properties of the circumanthracene molecule

In this paper, a systematic study of the electronic, optical, thermodynamic, optoelectronic, and nonlinear optical properties with RHF, B3LYP, wB97XD and BPBE methods using the cc-pVDZ basis set have been described to investigate the influence of fluorine (F) atom, which is an electron donor, on the circumanthracene (C40H16). Global reactivity descriptors, hole and electron transport properties were also calculated and compared with other studies on the same molecule. DFT/B3LYP results show that the undoped C40H16 molecule (Egap = 2.135 eV) and its fluorine-doped derivatives (C40F16 and C40H10F6) are semiconducting materials. However, doping the C40H16 molecule with the fluorine atom, partially or totally, favors the creation of a strong donor-acceptor system by considerably reducing its energy gap (Egap). The energy gap values of molecules doped using DFT/B3LYP method are 2.020 eV and 2.081 eV for the C40F16 and C40H10F6 molecules, respectively. These gap energies are below 3 eV, which favours the electronic properties of these molecules. They can be used to design organic solar cells. The nonlinear optical parameters were calculated and compared with those of urea. The values of βmol and μ calculated for C40F16 and C40H10F6 are higher than those of urea; this shows that these two materials have good nonlinear optical properties and therefore, are very good candidates for the design of optoelectronics and photonics devices. Futhermore, our results show that the perfluorination effect on the circumanthracene molecule increases the hole and electron reorganization energies, the vertical and adiabatic electron affinities and ionization energies, the optoelectronic and nonlinear optical properties, the transition excitation energy and the reactivity indices. The reorganization energies values suggest that these materials have promising transport properties. The natural bond orbital (NBO) analysis was also performed to determine the stability energy and charge delocalization in molecules. The theoretical results of the compounds studied in our work are in agreement with the experimental results. This confirms their molecular structures.

Optical properties of nanostructured antiviral and anticancer drugs

We present a computational study on the optical absorption properties of some systems of interest in the field of drug delivery. In particular we considered as drug molecules favipiravir (T705, an antiviral molecule) and 5-fluorouracil (5FU, an anticancer molecule) and, on the other hand, pure fullerenes (C24, B12N12, Ga12N12) and doped fullerenes (C23B, CB11N12) are considered as nanocarriers. Some combined configurations between the drug molecules and the carrier nanostructures have been then studied. The optical absorption properties of the above mentioned drug molecules and their carrier nanostructures in the free and bound states are obtained by a TD-DFT method, in gas phase and in aqueous solution. We perform a detailed analysis of the modifications arising in the absorption spectra that take place in some linked configurations between the drug molecules and the carrier nanostructures. These changes could be of importance as an optical fingerprint of the realized drug/carrier link.

A combined molecular dynamics simulation and DFT study on mercapto-benzamide inhibitors for the HIV NCp7 protein

Molecular dynamics and quantum simulations are performed to elucidate some aspects of the action mechanism of mercapto-benzamides, a proposed class of antivirals against HIV-1. These molecules act as prodrugs that, after modifications in the biological environment, are able to denature the HIV nucleocapsid protein 7, a metal binder protein, with two zinc finger motifs, vital for RNA maturation and viral replication. Despite their attractive features, these molecules and their biological target are not well understood. Simulations were performed to support a proposed action mechanism, based on the activation of mercapto-benzamides by acetylation, targeting a relatively rare protein hydrolyzed state, followed by trans-molecular acetylation from the molecule to the protein and finally the direct interaction of the molecular sulphur atom of mercapto-benzamides with the zinc atom coordinated by the protein. Our simulation results are in agreement with the NMR data about the zinc finger binding protein equilibrium configurations.

Feasibility of p-Doped Molecular Crystals as Transparent Conductive Electrodes via Virtual Screening

Transparent conducting materials are an essential component of optoelectronic devices. It is proven difficult, however, to develop high-performance materials that combine the often-incompatible properties of transparency and conductivity, especially for p-type-doped materials. In this work, we have employed a large set of molecular semiconductors extracted from the Cambridge Structural Database to evaluate the likelihood of transparent conducting material technology based on p-type-doped molecular crystals. Candidates are identified imposing the condition of high highest occupied molecular orbital (HOMO) energy level (for the material to be easily dopable), high charge carrier mobility (for the material to display large conductivity when doped), and a high threshold for energy absorption (for the material to absorb radiation only in the ultraviolet). The latest condition is found to be the most stringent criterion in a virtual screening protocol on a database composed of structures with sufficiently wide two-dimensional (2D) electronic bands. Calculation of excited-state energy is shown to be essential as the HOMO-lowest unoccupied molecular orbital (LUMO) gap cannot be reliably used to predict the transparency of this material class. Molecular semiconductors with desirable mobility are transparent because they display either forbidden electronic transition(s) to the lower excited states or small exchange energy between the frontier orbitals. Both features are difficult to design but can be found in a good number of compounds through virtual screening.

Investigation of oxygen influence to the optical properties of tirapazamine

New data on 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine) fluorescence has been obtained using the Perkin-Elmer Lambda 950 UV-Vis-NIR spectrophotometer experimental technique in combination with the extensive DFT-theory approach. Based on the results obtained, we revealed that the optical properties of the molecule under study remain significantly unchanged when the number of oxygen substitutions decreases from 2 to 0. Here we also present the results of the study of the influence of acetonitrile and ethyl acetate on the fluorescence of tirapazamine with the different number of oxygen atoms. Results of our investigation indicate the formation of anion in the case of 3-amino-1,2,4-benzotriazine 1,4-dioxide with two oxygen atoms and their transformation to tirapazamine with one oxygen atom.

Time-Dependent Density Functional Theory Investigation on the Electronic and Optical Properties of Poly-C,Si,Ge-acenes

We report a comparative computational investigation on the first six members of linear poly-C,Si,Ge-acenes (X4n+2H2n+4, X = C,Si,Ge; n = 1, 2, 3, 4, 5, 6). We performed density functional theory (DFT) and time-dependent DFT calculations to compare morphological, electronic, and optical properties. While C-acenes are planar, Si- and Ge-acenes assume a buckled configuration. Electronic properties show similar trends as a function of size for all families. In particular, differently from C-based compounds, in the case of both Si- and Ge-acenes, the excitation energies of the strongest low-lying electronic transition (β peaks) span the visible region of the spectrum, demonstrating their size tunability. For all families, we assessed the plasmonic character of this transition and found a linear relationship for the wavelength-dependence of the β peaks as a function of the number of rings. A similar slope of about 56 nm is observed for Si- and Ge-acenes, although the peak positions of the former are located at lower wavelengths. Outcomes of this study are compared with existing theoretical results for 2D lattices and nanoribbons, and experiments where available.

Nature (Hole or Electron) of Charge-Transfer Ability of Substituted Cyclopyrenylene Hoop-Shaped Compounds

We theoretically investigate here by means of DFT methods how the selective substitution in cyclic organic nanorings composed of pyrene units may promote semiconducting properties, analyzing the energy needed for a hole- or electron-transfer accommodation as a function of the substitution pattern and the system size (i.e., number of pyrene units). We choose to study both [3]Cyclo-2,7-pyrenylene ([3]CPY) and [4]Cyclo-2,7-pyrenylene ([4]CPY) compounds, the latter already synthesized, with substituents other than hydrogen acting in ipso and ortho positions, as well as the effect of the per-substitution. As substituents, we selected a set of electroactive halogen atoms (F, Cl, and Br) and groups (CN) to disclose structure-property relationships allowing thus to anticipate the use of these systems as organic molecular semiconductors.

Substitution Effects on the Optoelectronic Properties of Coumarin Derivatives

Coumarin derivatives have gathered major attention largely due to their versatile utility in a wide range of applications. In this framework, we report a comparative computational investigation on the optoelectronic properties of 3-phenylcoumarin and 3-heteroarylcoumarin derivatives established as enzyme inhibitors. Specifically, we concentrate on the variation in the optoelectronic characteristics for the hydroxyl group substitutions within the coumarin moiety. In order to realize our aims, all-electron density functional theory and time dependent density functional theory calculations were performed with a localized Gaussian basis-set matched with a hybrid exchange–correlation functionals. Molecular properties such as highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies, vertical ionization (IEV) and electron affinity energies, absorption spectra, quasi-particle gap, and exciton binding energy values are examined. Furthermore, the influence of solvent on the optical properties of the molecules is considered. We found a good agreement between the experimental (8.72 eV) and calculated (8.71 eV) IEV energy values for coumarin. The computed exciton binding energy of the investigated molecules indicated their potential optoelectronics application.

A computational study on the electronic and optical properties of boron-nitride circumacenes

We report a comparative and systematic computational analysis on the electronic and optical properties of the boron-nitride-made (BN) counterparts of the carbon-made circumacenes. Recently, these planar molecules have attracted interest for applications in the condensed matter physics domain. In particular, we focus on the five first members of this BN-family (from BN-coronene to BN-circumpentacene) presenting a comparison with their carbon analogues. For all the systems investigated, we calculate different electronic properties and the optical absorption spectra, performing all electron Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) calculations. In the context of ab initio calculations we select a localized Gaussian basis-set matched with a hybrid exchange-correlation functional. We discuss possible implications of the observed BN cluster properties, which could be an alternative material or complementar as compared to their carbon analogues. In particular, concerning the optical properties, we have found that the main difference between the two families is that the BN molecules absorb in the UV, rather than in the visible as happens for the C-made parents. Moreover, we demonstrate that the electronic and optical observables of the BN clusters are nearly independent of the cluster size in contrast to what happens for their carbonaceous counterparts.

Vibrational and optical characterization of s-triazine derivatives

The optical and electron properties of three different s-triazine derivatives are investigated to ascertain the role of the donor acceptor character in amine-triazine systems depending on the bridging radical of the ammine group. The three derivatives were obtained starting from three different ammine compounds allowing to achieve a structure with a triazine core, surrounded by three ammine group and terminated with cyano or methyl or oxy-methyl functional group. Experimental optical data were interpreted in view of the electronic insights gathered by means of density functional theory simulations on base compounds. As compared to the reference electron donating triazine core, the resulting compounds show different donor acceptor character, from electron accepting to electron donating feature. Among the analyzed derivatives, the cyano terminated ammino-triazine compound shows the most promising optical features for photonics and lighting applications.

Deciphering Molecular Mechanisms of Interface Buildup and Stability in Porous Si/Eumelanin Hybrids

Porous Si/eumelanin hybrids are a novel class of organic-inorganic hybrid materials that hold considerable promise for photovoltaic applications. Current progress toward device setup is, however, hindered by photocurrent stability issues, which require a detailed understanding of the mechanisms underlying the buildup and consolidation of the eumelanin-silicon interface. Herein we report an integrated experimental and computational study aimed at probing interface stability via surface modification and eumelanin manipulation, and at modeling the organic-inorganic interface via formation of a 5,6-dihydroxyindole (DHI) tetramer and its adhesion to silicon. The results indicated that mild silicon oxidation increases photocurrent stability via enhancement of the DHI-surface interaction, and that higher oxidation states in DHI oligomers create more favorable conditions for the efficient adhesion of growing eumelanin.

Anthanthrene dye-sensitized solar cells: influence of the number of anchoring groups and substitution motif

Four anthanthrene-based molecules were synthesized as sensitizers in dye-sensitized solar cells, leading to the best overall efficiency up to 5.3%.