Absorption and Emission of the Apigenin and Luteolin Flavonoids: A TDDFT Investigation

Abstract

The absorption and emission properties of the two components of the yellow color extracted from weld (Reseda luteola L.), apigenin and luteolin, have been extensively investigated by means of DFT and TDDFT calculations. Our calculations reproduce the absorption spectra of both flavonoids in good agreement with the experimental data and allow us to assign the transitions giving rise to the main spectral features. For apigenin, we have also computed the electronic spectrum of the monodeprotonated species, providing a rationale for the red-shift of the experimental spectrum with increasing pH. The fluorescence emission of both apigenin and luteolin has then been investigated. Excited-state TDDFT geometry optimizations have highlighted an excited-state intramolecular proton transfer (ESIPT) from the 5-hydroxyl to the 4-carbonyl oxygen of the substituted benzopyrone moiety. By computing the potential energy curves at the ground and excited states as a function of an approximate proton transfer coordinate for apigenin, we have been able to trace an ESIPT pathway and thus explain the double emission observed experimentally.

Spatially Resolved Plant Metabolomics: Some Potentials and Limitations of Laser-Ablation Electrospray Ionization Mass Spectrometry Metabolite Imaging

“…These metabolites showed an absorption maximum at 332 nm with a second peak at 260 nm. This, together with the C 15 H 11 O 5 MS/MS fragment, corresponds to apigenin-derived flavonoid structures (Amat et al, 2009). …”

Spectroscopic Properties of Flavonoids in Various Aqueous-Organic Solvent Mixtures

“…20 It is worth noting that ESIPT can also occur at the API from 5-OH to O-11 in the S 1 geometry, the same way as the QCT. 35 However, for both QCT and API, the S 2 state should be much less susceptible to ESIPT than the S 1 state. 20 Similarly, because the π,π* and n,π* states are close together and the nuclear frameworks are significantly different in these electronic states, internal conversion will occur rapidly.…”

“…15,19,20 However, contrary to the case of QCT, the ESIPT of API to produce the enol tautomer at the S 1 state cannot occur quickly because the dihedral angle between the B ring and γ-pyrone ring should decrease to cause ESIPT after excitation. 35 Several theoretical studies for API suggest that upon excitation to the Franck-Condon (FC) point, the first relaxation process occurs through molecular planarization. From the FC region, the excited state energy decreases rapidly to a flat region that corresponds to the ESIPT minimum structure.…”

“…The S 1 → S o fluorescence emission of API may be due to the emission from an excited state structure that has not yet undergone the ESIPT process. 33,35 If these molecules are excited to the S 1 state, QCT does not emit any significant fluorescence, but API exhibits strong fluorescence emission in organic solvents. For QCT and API, ESICT can occur, whereas the ESIPT can not at the S 2 state in organic solvents.…”

An ab initio simulation of the UV/Visible spectra of substituted chalcones

“…On the other hand, using ab initio CIS/HF, Oumi et al [22] studied chalcone and its hydroxyl derivatives, but the differences reported between gas-phase theoretical and solvated experimental λ max are quite large (0.7eV on average). In recent years, time-dependent density functional theory (TD-DFT) has emerged as a reliable standard tool for the theoretical treatment of electronic excitation spectra and recent works demonstrate the good accuracy for a wide range of systems [23][24][25][26][27][28][29][30][31][32][33][34]. Moreover, the computational cost of TD-DFT calculation is comparative to that of a Hartree-Fock based single excitation theory, such as, configuration interaction singles (CIS) or time-dependent Hartree-Fock (TDHF) method.…”