A study of TDDFT performance in modeling of spectral changes induced by interactions of ketocyanine dyes with inorganic ions

Origin of Substituent Effect on Tautomeric Behavior of 1,2,4-Triazole Derivatives: Combined Spectroscopic and Theoretical Study

The reaction of 2-aryl-[1,2,4]triazolo[1,5-c]quinazolines with nucleophilic reagents (hydrazine hydrate, sodium hydroxide, sodium methoxide, hydrochloric acid) under acidic conditions leads to formation of compounds that tend to tautomerize. The products of the transformation are distinguished by the position (ortho-, meta-, para-) of the OCH₃ group in the aryl moiety. To assign their structures we used the combined approach: experiment and theoretical modeling. The procedure included calculation of the relative stability for possible tautomers, simulation of UV/vis spectra for the most stable forms, and comparison of the resulting curves with the experimental spectral data taking into account the Boltzmann weighting. Through computations, we showed that the orientation of OCH₃ substituent remarkably impacts on the tautomeric behavior of triazoles. In the case of ortho-OCH₃ it is controlled by formation of the intramolecular hydrogen bond while for meta- and para- derivatives the degree of conjugation plays the decisive role. In order to balance the accuracy and cost of calculations we evaluated the performance of selected DFT methods and 6-31G*, 6-311++G**, and STO^##-3G_el basis sets. The last one is a physically justified basis set previously constructed in our group, and its combination with PBE1PBE approach is shown to be the best choice for UV/vis simulations in the frame of the current research.

Dye chemistry with time-dependent density functional theory

In this perspective, we present an overview of the determination of excited-state properties of "real-life" dyes, and notably of their optical absorption and emission spectra, performed during the last decade with time-dependent density functional theory (TD-DFT). We discuss the results obtained with both vertical and adiabatic (vibronic) approximations, choosing relevant examples for several series of dyes. These examples include reproducing absorption wavelengths of numerous families of coloured molecules, understanding the specific band shape of amino-anthraquinones, optimising the properties of dyes used in solar cells, mimicking the fluorescence wavelengths of fluorescent brighteners and BODIPY dyes, studying optically active biomolecules and photo-induced proton transfer, as well as improving the properties of photochromes.

Time-dependent density functional theory calculations of the solvatochromism of some azo sulfonamide fluorochromes

The absorption and emission spectra of three azo sulfonamide compounds in different solvents were investigated theoretically by using response functions combined with density functional theory (DFT), while the solvent effect on the structure and the electronic transitions was determined using the integral equation formalism for the polarizable continuum model (IEF-PCM). The results show that the applied different exchange-correlation functionals can reproduce the experimental values well. DFT calculations of the title compounds showed that the H-bond formed between the solute and solvent molecules is one of the major causes of the reversible solvatochromism observed in measured spectra. This is due to a better stabilization of the neutral form than the zwitterionic form in the polar protic solvents, which is characteristic of the hypsochromic shift. On the other hand, the molecules considered exhibit a monotonic behavior regarding the polarity of the low-lying excited state (Δμg-CT) as a function of the solvent polarity. This dependence occurs in the case of the positive solvatochromism and confirms the thesis regarding the H-bond solute-solvent interactions. Theoretically determined values of the two-photon cross section revealed that the (σOF(2)) shows similar trends with changes in λabs, in contrast to <δ(OF)> values. In conclusion, the results demonstrate that the investigated molecules can be used successfully as fluorochromes in bioimaging.

Fluorescence of tryptophan in aqueous solution

In this work, the absorption and emission spectra of Tryptophan (Trp) in aqueous solution were studied. Moreover, a hydrogen-bonded zwitterionic Trp(H2O)9 model was proposed and its ground-state and excited-state properties were investigated using the density functional theory (DFT) and the time-dependent density functional theory (TD-DFT) methods, respectively. All spectroscopic data in our experiments can be well explained by the hydrogen bond strengthening in the excited state of the model complex. The delocalization of electron density between indole moiety and neighboring H2O molecules in fluorescent state was proposed to be facilitated by the strengthened hydrogen-bond chain, and thus resulting in the large red-shift fluorescence of Trp in aqueous solution.

Interaction of alkali, alkaline earth and transition metal ions with a ketocyanine dye: a comparative electronic spectroscopic study

Interaction of a dye which is structurally similar to a ketocyanine dye with metal ions (alkali, alkaline earth and transition metal) has been studied by monitoring the electronic absorption, steady state and time resolved fluorescence parameters of the dye. The dye (S(0) state) forms a 1:1 complex with cations as indicated by the appearance of a new band at a longer wavelength. Equilibrium constant and other thermodynamic parameters for complexation have been determined. The interaction between the dye and the cation is mostly electrostatic in nature. Spectroscopic results have been supplemented by DFT calculation. For very low concentration of cations, where complexation is insignificant, the absorption band of the dye undergoes a slight blue shift. Enhancement of fluorescence intensity has been observed in the same concentration range. Both phenomena have been explained in terms of formation of a weak association complex where one/more cation replace equivalent solvent molecules in the cybotatic region around the dye. The binding constant of the weak association complex involving cation and the dye (S(1) state) has been determined and has been found to depend on the charge-to-size ratio of the cations. Measurement of fluorescence lifetime of the dye indicates that the association complex is slowly decaying relative to solvated dye. At higher concentration of metal ions, however, fluorescence of the dye is quenched by the metal ions. A red shift of fluorescence maximum has also been observed in this concentration range.

A DFT/TDDFT study on spectral effects of metal ion interactions with benzofurazan-based fluorescent probes

CAM-B3LYP DFT/TDDFT calculations have been performed on two fluorescent benzofurazan derivatives and their complexes with metal ions (Zn(2+), Na(+), K(+), Mg(2+) and Ca(2+)). Optimized structures of complexes and binding energies have been determined. Calculated vertical transition energies have been compared to available experimental data. Only one ligand binds effectively Zn(2+) ion allowing metal orbitals to participate in frontier molecular orbitals which results in significant shifts in absorption and emission spectra. Modified structure of the other ligand makes ion binding less effective. It has been shown that proper reproduction of transition energies requires accounting for state-specific solvation.

The effect of zinc ion on the absorption and emission spectra of glutathione derivative: predication by ab initio and DFT methods

Relying on the reaction of o-phthalaldehyde (OPA) with glutathione (GSH) to form a highly fluorescence derivative GSH-OPA has been widely used to measure reduced glutathione. In order to better understand spectra property of the GSH-OPA and the effect of zinc ion on it, the ground and the lowest singlet excited state properties, the electronic absorption and emission spectra are predicted by ab initio and DFT methods. The absorption spectra are simulated using time dependent DFT method (TD-DFT) whereas the emission spectra are approximated by optimizing the lowest singlet excited state by HF/CI-Singles and then subsequently using this geometry for the TD-DFT calculations. The solvent effects on transition energies have been described within the conductor-like polarizable continuum model (CPCM). The calculated transition energies (absorption and emission) are in agreement with available experimental information.