Browsing by Author "Berber, Halil"

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Effects of Enol-Imine/Keto-Amine Tautomerism and Conformational Changes on the Electronic Spectra of a Novel 1,2,4-Triazole Ortho-Hydroxyaryl Schiff Base in Different Solvents
(Elsevier, 2023) Sıdır, İsa; Sıdır, Yadigar Gülseven; Berber, Halil; FAUSTO, RUI
In this study, a novel o-hydroxyaryl Schiff base bearing the 1,2,4-triazole heterocyclic core, (E)-2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-6-methoxyphenol, was synthesized and structurally characterized by NMR (1H-and 13C-) and IR spectroscopies as well as by Density Functional Theory (DFT) electronic structure calculations. The compound was then investigated by UV-Vis absorbance and fluorescence emission spectroscopies in different solvents. The wavelength shifts observed in the band corresponding to the lowest energy transition in the absorbance spectra upon changing the solvent, as well as in the emission bands observed in the fluorescence spectra (upon excitation at 310 nm) were explained considering the effects of solvent-induced conformational changes and photoinduced enol-imine/keto-amine tautomerism. The interpretation of the experimental results was supported by structural data calculated for the different isomeric forms of the compound and of their electronic spectra in the gas phase and in solvents of different polarity. Solvent effects were also evaluated at the light of the Kamlet-Taft and Catal & PRIME;an solvatochromic models.
Open Access
Reversal in Solvatochromism, Photochromism and Thermochromism in a New Bis-azo Dye Based on Naphthalen-1-amine
(Elsevier B.V., 2024) Sıdır, İsa; Kara, Yunus Emre; Sıdır, Yadigar Gülseven; Berber, Halil; FAUSTO, RUI
A novel bis-azo dye, 4,4′-((1E,1′E)-(oxybis(4,1-phenylene))bis(diazene-2,1-diyl))bis(naphthalen-1-amine) (abbreviated as 4odna) was synthesized and characterized by IR and 1H, 13C and 2D COSY-NMR spectroscopies, and mass spectrometry. Optical properties were evaluated using UV–vis absorption spectroscopy. The observed solvatochromism was ascribed to the presence of different azo or/and hydrazone forms in solution. The azo forms show both positive and negative solvatochromism, with the reversal occurring for solvents with ET(30) ∼45 kcal mol−1, while the hydrazone tautomer shows negative solvatochromism. Application of the multiparametric Catalán and Kamlet-Taft linear solvation energy models allowed to evaluate the dependence of the solvatochromism exhibited by 4odna on the hydrogen bond donating (HBD) and accepting (HBA) abilities of the solvent, as well as on their dipolarity (SdP) and polarizability (SP). Upon UV (λ = 311 nm) irradiation at room temperature, the compound was found to exhibit similar photochromic behavior in the polar-protic solvents methanol and ethanol, which is distinct from that observed in the polar-aprotic solvents dichloromethane, chloroform and chlorobenzene, with the hydrazone tautomer being photoconverted into the azo tautomer in the first group of solvents and vice-versa in the second group. In acetone, UV irradiation extensively transforms the compound into species with no absorption in the visible range, leading to fast discoloration of the solution. Temperature dependence of the color of the solutions of 4odna in ethanol and chlorobenzene was also evaluated, and reversible thermochromic behavior was observed in the first solvent. In chlorobenzene, no thermochromism was observed, but a change of color of the solution was promptly induced by the UV–vis broadband source beam of the spectrometer when the absorbance spectrum of the solution was being recorded at T = 115 °C, which demonstrates that the azo forms of 4odna undergo easy phototransformation into the hydrazone forms in this solvent at high temperature. © 2023 Elsevier B.V.
Open Access
UV-induced-OCH3 Rotamerization in a Matrix-Isolated Methoxy-Substituted Ortho-Hydroxyaryl Schiff Base
(Springernature, 2022) Sıdır, İsa; Sıdır, Yadigar Gülseven; Gobi, Sandor; Berber, Halil; ILDIZ, GÜLCE ÖĞRÜÇ; Fausto, Rui
A new methoxy-substituted ortho-hydroxyaryl Schiff base, 4-(3-methoxy-2-hydroxybenzylidene-amino) phenol was synthesized from 4-aminophenol and 2-hydroxy-3-methoxybenzaldehyde in methanol solution and characterized by H-1-NMR, C-13-NMR and infrared spectroscopies and elemental analysis. The compound was isolated in a cryogenic (10 K) argon matrix, and the analysis of the infrared spectrum of the matrix-isolated compound revealed that it corresponds to the E-enol-imine isomeric form, with 3 different conformers being present in the matrix. These conformers share as common structural features the conformation of the free hydroxyl group (trans relatively to the para-substituent of the ring) and the presence of an OH center dot center dot center dot N intramolecular H-bond involving the methoxy-substituted phenol ring and the azomethine bridge, while they differ in the orientation of the methoxy-substituent group. The structures and relative energies of the conformers of the molecule, and relevant barriers for their interconversion were obtained through quantum chemical calculations, which were also used to calculate the infrared spectra of the different forms. Calculations were also carried out for the higher-energy Z-enol-imine and keto-amine forms of the compound. Upon UV (230 nm) irradiation, -OCH3 rotamerization was observed, leading to conversion of the lowest energy conformer, where the methoxy group is aligned with the plane of the ring, into the other two conformers initially present in the matrix, in which the OCH3 group is out-of-the-plane of the ring. As for other phenolic compounds previously studied, spontaneous quantum mechanical tunneling conversion of the cis-OH conformers present in the gas-phase into the three observed conformers was found to take place during matrix deposition.