Absorption spectra of Nitrazine Yellow indicator. Experimental data and quantum chemical evaluations
This article presents an experimental investigation and theoretical analysis of the electronic absorption spectra of the indicator nitrazine yellow (NY) in aqueous solutions. Quantum chemical modeling of electronically excited states is performed within the framework of time-dependent density functi...
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| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
V. N. Karazin Kharkiv National University
2024-06-01
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| Series: | Вісник Харківського національного університету: Серія xімія |
| Subjects: | |
| Online Access: | https://periodicals.karazin.ua/chemistry/article/view/24536 |
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| Summary: | This article presents an experimental investigation and theoretical analysis of the electronic absorption spectra of the indicator nitrazine yellow (NY) in aqueous solutions. Quantum chemical modeling of electronically excited states is performed within the framework of time-dependent density functional theory (TD-DFT). A variety of approaches and basis sets are explored, particularly focusing on the B3LYP and CAM-B3LYP functionals. The standard 6-31+G(d,p) basis set is employed, along with combinations using pseudopotential basis sets for Na and S atoms.
In the first variant of calculations, the LanL2DZ basis set (and corresponding pseudopotential) is used for all atoms within the molecules. In the second variant, the LanL2DZ basis set is applied exclusively to Na and S atoms, while the standard valence double-zeta split basis set 6-31+G(d,p) is utilized for the remaining elements (H, C, N, O). Solvent effects on the absorption spectra are incorporated using the polarizable continuum model, employing the linear response method.
Calculations are performed on three forms of NY. Two of these forms (A and B) correspond to azo-hydrazone tautomerism, while the third form (C) represents the deprotonated state. Ground state geometry calculations indicate that the π-conjugated part of form A is largely planar and stabilized by an intramolecular hydrogen bond O-H...N. The tautomeric form B is also characterized by a high degree of planarity in its conjugation system. In contrast, the deprotonated form C shows significant rotation of the 2,4-dinitrophenyl group and the nitro group in the ortho position of the benzene ring.
Analysis of excited-state calculations for the three forms of NY reveals that both variants (B3LYP/LanL2DZ and B3LYP/LanL2DZ/6-31+G(d,p)) require minimal computational resources while producing results that correspond well with the experimentally observed absorption bands. |
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| ISSN: | 2220-637X 2220-6396 |