Browsing by Author "Costa, Rene"

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Betanidin isomerisation and decarboxylation, thermodynamic and charge transfer dye properties towards dye sensitised solar cells application
(John Wiley & Sons, Inc., 2021-01-25) Costa, Rene; Pogrebnoi, Alexander M.; Pogrebnaya, Tatiana P.
Along with attractiveness of natural dyes for solar technologies, the instability is a well‐known drawback of the dyes, which impedes their usage for dye sensitised solar cells (DSSCs) application. The planar isomer appeared to be predominant in equilibrium vapour despite its less energetic stability. Both betanidins belong to red–purple pigments betacyanins, which experimentally demonstrated good adsorption in a visible range. In this study, the structural, thermodynamic, and optoelectronic properties of betanidins have been determined from density functional theory (DFT) and time‐dependent DFT (TD–DFT) computations. On the basis of the thermodynamic approach, isomerisation reaction between two structural conformers of betanidin, bent and planar, and also decarboxylation reactions have been analysed. The planar isomer appeared to be predominant in equilibrium vapour despite its less energetic stability; both betanidin molecules exhibit an inclination to decay into decarboxylated betanidin and CO2. As for worthy optoelectronic properties and applicability in DSSCs, the dyes considered satisfy most requirements to sensitise the semiconductor TiO2 and be regenerated by electrolytes. Adsorption of the dyes at the TiO2 surface has been simulated; for the dye@TiO2 complexes, the binding energies, electronic spectra, and relevant molecular orbital (MO) isosurfaces have been computed and discussed.
Combination of natural betanidin dye with synthetic organic sensitiser towards dye-sensitised solar cell application
(NM-AIST, 2023-05) Costa, Rene
Betanidins belong to natural red-purple pigments betacyanins, which experimentally demonstrated good light adsorption in a visible range and might be suitable for the dye sensitised solar cell (DSSCs). Instability is a well-known drawback of natural dyes, which impedes their use for DSSCs. A thermodynamic approach helps to understand the betanidin (Bd) instability which occurs due to spontaneous decarboxylation reaction with decarboxylated betanidin (dBd) formation. The study considers the improvement of the sensitiser’s functionality via combination of natural Bd/dBd dyes and synthetic 4- (Diphenylamino)phenylcyanoacrylic acid (L0) dye. Novel complex D–π–A organic dyes, L0–Bd and L0–dBd with structural isomers, have been designed via esterification reactions. The DFT/B3LYP5/6‒31G(d,p) approach has been used to compute geometry, vibrational spectra and thermodynamic characteristics of the individual isomers and their complexes with L0. Implementation of TD–DFT method aids in obtaining optoelectronic properties. The broader coverage of the solar spectrum with greater light-harvesting efficiency was achieved for the complexes compared to individual dyes. The dyes attachment to the semiconductor TiO2 was simulated in terms of different adsorption modes to hydrogenated (TiO2)6 cluster. Binding energies and electronic spectra of the dye@TiO2 systems were computed, and electron density distributions over frontier molecular orbitals analysed. Binding energy magnitudes varied within 15‒21 eV for the dye@TiO2 systems.
Effect of Electron Donor Groups on Optoelectronic Properties of Betalain Dyes: A DFT Study
(wiley, 2025-05) Tsere, Melkizedeck; Costa, Rene; Deogratias, Geradius; Pogrebnaya, Tatiana; Pogrebnoi, Alexander; Machunda, Revocatus; Al-Qurashi, Ohoud; Wazzan, Nuha; Babu, Nambury
A sensitizer is a vital component of dye-sensitized solar cells(DSSCs); it absorbs incident photons, excites electrons, and facil-itates charge transfer to the semiconductor. In the present work,modification of betalain dyes through grafting of electron donorgroups has been performed. The reported optoelectronic properties of the investigated dyes are determined using densityfunctional theory (DFT) and time-dependent DFT methods. The investigated sensitizers exhibit maximum absorption between400 and 442 nm with light-harvesting efficiencies exceeding 93%.Favorable interactions are observed between the dyes and the hydrogenated TiO2 cluster, (TiO2)6H3. The obtained binding energies range from 1.39 to 0.97 eV in the gas phase and 0.31 to 0.03 eV in water. The electronic spectra of the dye@TiO2 complexes show broader and intensive bands with bathochromicshifts when compared to the individual dyes. The charge density distribution in the complexes indicates appropriate ability of thedyes for charge injection to the semiconductor. Among the considered dyes, the most promising candidates for use in DSSCs have been selected.
Enhancing the optoelectronic properties of blended triphenylamine-betalain based dyes through tailoring the anchoring unit: a theoretical investigation
(Taylor & Francis, 2024-11-25) Tsere, Melkizedeck; Costa, Rene; Deogratias, Geradius; Al-Qurashi, Ohoud; Wazzan, Nuha; Pogrebnaya, Tatiana; Pogrebnoi, Alexander; Machunda, Revocatus
A series triphenyl-betalain organic dyes featuring carboxylic acid and nitro anchoring groups CH = C(X)COOH for the A1-X dyes and -CH = C(X)NO2 for the A2-X dyes, respectively, where X = CN, CH3, CCl3 and CF3 was evaluated for dye sensitised solar cells application. The geometrical structures, molecular orbitals and energies, light absorption patterns, free energies of electron injection and dye regeneration and binding to the semiconductor have been explored using DFT/TD-DFT methods. The nitro-based anchoring group resulted in pronounced red-shift in absorption spectra between 111 and 317 nm compared to carboxylic acid-based dyes. Attachment of the dyes to the semiconductor was modelled via binding to (TiO2)6H3 cluster; A2-X dyes exhibited more stable Dye@TiO2 complexes with binding energies (BEs) ranging between −4.08 and −2.88 eV compared to A1-X dyes with BEs range of −1.11 to −0.05 eV. The results evince that the dyes with CH = C(X)NO2 anchoring groups could be promising materials for light harvesting application.
Structure and vibrational spectra of cluster ions over rubidium iodide by computational chemistry
(IEEE, 2015-03-05) Costa, Rene; Pogrebnaya, Tatiana P.; Pogrebnoi, Alexander M.
The properties of Rb 2 I + , RbI 2 - , Rb 3 I 2 + and Rb 2 I 3 - ions were studied using two quantum chemical methods, DFT and Møller-Plesset perturbation theory of the 2 nd order. The effective core potential with Def2-QZVP basis set for rubidium atom and SDB-aug-cc-pVTZ basis set for iodine atom were used. According to the results, the equilibrium geometric structure of the triatomic ions was found to be linear of D ∞h symmetry. For the pentaatomic ions, the three isomeric forms were found: the linear (D ∞h ), the kite-shaped (C 2v ), and the bipyramidal (D 3h ), both for the positive and negative ions. For all species, the equilibrium geometric parameters and vibrational spectra have been determined.