Spectral-luminescent properties and photolysis of charged forms (cation and anion) of bisphenol A are studied experimentally and by methods of quantum chemistry. The calculations and the experiment ...demonstrate that no new absorption bands appear in the absorption spectra of charged forms in the region of 200–600 nm as compared to a neutral molecule. The polar solvent (water) shifts the absorption spectrum bands of the ionic forms to the region of low energies. In this case, the shift of cation absorption spectrum is insignificant, while the shift of anion absorption spectrum is significant as the intensity of absorption bands increases. The low quantum yield of fluorescence of ionic forms is explained by the predominance of singlet-triplet conversion efficiency over the efficiency of the radiation channel of fluorescent state decay. The low quantum yield of fluorescence of the anion form is due not only to the effective singlet-triplet conversion, but also to the low efficiency of the radiation decay of the fluorescent state of the anion caused by a change in its orbital nature. Calculations demonstrate that the potential curves of the excited states of bisphenol A and its ionic forms have a significant potential barrier for photolysis. An increase in the potential reaction barrier in the cation decreases the efficiency of its photolysis. The increase in the photodissociation efficiency of the bisphenol A anion is caused by a noticeable decrease in the potential barrier and an increase in the overlap between the absorption spectra of the bisphenol A anion and the solar radiation.
V. G. Plotnikov: Life in Science Mayer, G. V.; Artyukhov, V. Ya; Bazyl’, O. K.
Russian physics journal,
12/2020, Letnik:
63, Številka:
8
Journal Article
Recenzirano
The role of Professor V. G. Plotnikov in the development of the theoretical molecular photonics is discussed. A review is given of the principal results and the list of his publications covering the ...creation of the Nurmukhametrov–Plotnikov–Shigorin spectral-luminescent systematics of molecules. The main results of the theory for the radiationless conversion in polyatomic molecules, constructed by V. G. Plotnikov, are presented.
The stages of development of molecular photonics at Tomsk State University are presented. It was A. N. Terenin’s student, N. A. Prilezhaeva, who pioneered the Russian photochemistry and fostered the ...development of a Tomsk school of spectroscopists, at that time the only research team in the Asian part of Russia. In 1950, the research in the field of molecular spectroscopy and quantum chemistry of complex molecules was initiated by a Prilezhaeva’s student, V. I. Danilova, who became a TSU Professor at a later date. Fundamental problems were posed and solved, which related the spectra and the electron shell structure with the physical-chemical properties of several classes of complex organic molecules. The generalizations made by Danilova were quite valuable for the theory of molecular spectra and helped forming her own scientific school in 1970−80s.
The spectral-luminescent properties and photolysis of phenol and some of its derivatives have been considered experimentally and by methods of quantum chemistry. It has been shown that the ...substitution with a methyl group (
p
-cresol) and the introduction of the second benzene ring (bisphenol A) lead to a shift of absorption bands toward longer wavelengths and some changes in their intensity. The non-planar structure of
p
-cresol and bisphenol A promotes an increase in the efficiency of singlet-triplet conversion and a decrease in the fluorescence quantum yield. Results of calculations have established the mechanisms of photolysis of the considered molecular systems. It has been shown that the O–H bond in phenol and
p
-cresol is broken by the pre-dissociation mechanism. Photolysis of bisphenol A upon exposure to solar radiation proceeds by the mechanism of direct dissociation, but with a noticeable potential barrier (~12000 cm
–1
).
The absorption and fluorescence spectra of sulfaguanidine, its complexes with hydrogen bonds, and doubly charged cationic forms have been studied experimentally and theoretically. The orbital nature ...of electronically excited states is established and a theoretical interpretation of the absorption and fluorescence spectra is given. It was shown that the main reason for the anomalously large Stokes shift of fluorescence is the rearrangement of the benzoid structure of the phenyl fragment of sulfaguanidine into a quasi-quinoid one. The influence of the formation of hydrogen bonds and the addition of a proton on the amount of charge transfer between weakly bound fragments of the molecule has been established.
The absorption and fluorescence spectra of charged anionic and cationic forms of bisphenol A (BPA) have been studied. The nature of electronically excited states and the photolysis of the BPA ...molecule have been interpreted based on results of quantum chemical calculations. The BPA spectra in an aqueous solution are compared during transition from the neutral to the ionic form. Results of calculations have shown that the small value of the fluorescence quantum yield in all examined molecular structures is determined by the high efficiency of the singlet-triplet conversion. In the anionic BPA form, a decrease in the efficiency of radiation decay channel by two orders of magnitude has been recorded caused by a change in the orbital nature of the fluorescent state compared to the neutral and cationic forms. It is shown that the probability of photolysis of the molecule under study increases due to the overlap of the absorption spectra of the anionic form in an aqueous solution under exposure to sunlight.
The spectral-luminescent properties of the charged (anionic and cationic) forms of three biologically active substituted benzaldehydes, namely,
o
-anisaldehyde (2-methoxybenzaldehyde), syringaldehyde ...(3,5-dimethoxy-4-hydroxybenzaldehyde), and vanillin (3-methoxy-4-hydroxybenzaldehyde), are studied by quantum-chemical methods. Calculations show that the
S
1
state of the charged forms of the studied molecules, in contrast to the neutral forms, is of the ππ* type, and its localization is similar to the localization of the
S
2
(ππ*) state of the neutral molecules (anisaldehyde and vanillin) or of the
S
3
(ππ*) state of syringaldehyde. According to the calculation results, the spectral range of 240–420 nm contains no new absorption bands corresponding to electronic transitions differing in nature and localization from the electronic transition of the neutral molecules. The calculated fluorescence characteristics of the charged forms of the studied molecules show that the radiative decay rate of the charged forms is considerably higher than that of the neutral forms, which is related to the different orbital nature of the
S
1
state in the neutral and charged forms. Analysis of the calculated and experimental data on the fluorescence of the studied substituted benzaldehydes in alcohol solutions reveals that the fluorescence at 410 nm belongs to the cationic forms. Vanillin and syringaldehyde may also exhibit weak fluorescence of their anionic forms.
Substituted benzaldehydes, which are widespread in nature, exhibit antibacterial, anti-inflammatory, antiviral, and anticarcinogenic activity with low toxicity, which makes them promising in ...medicine. The results of an experimental and theoretical study of the spectral-luminescent properties of four neutral forms of hydroxy- and methoxy-substituted benzaldehydes are presented. The absorption spectra of the studied compounds in hexane and ethanol were obtained. The spectra of fluorescence and fluorescence excitation of the substances in ethanol solutions were measured. Based on quantum chemical calculations, the orbital nature of electronic transitions, the features of the electron density distribution upon excitation, and changes in the structure of the compound are determined and the rate constants of photophysical processes are estimated. According to calculations, in all the compounds studied, the
S
1
state is formed by the
n
π* transition and the intensity of the long-wavelength bands in these compounds is formed by one or two ππ* transitions. The fluorescence quantum yield is estimated from experimental and theoretical data. The results of analysis and comparison of experimental data with the results of quantum chemical calculations allow a conclusion that the neutral forms of the studied substituted benzaldehydes are not responsible for the fluorescence observed in experiments with ethanol solutions.
A quantum chemical study of the spectral and luminescent properties of the BPA + 2
H
2
O
complex was carried out. Calculations were performed by the semi-empirical method of intermediate neglect of ...differential overlap using a program complex and a special parameterization. The spectral behavior of BPA in water was modeled by a complex with water molecules in the ratio 1: 2 forming the hydrogen bond. The calculated data were compared with the results of investigation of the isolated BPA molecule. The nonplanar BPA structure leads to the strong mixing of the π- and σ-type atomic wave functions. The main reason for the low quantum yield of the BPA fluorescence is the efficient process of singlet-triplet conversion in the
S
1
(ππ*) ≳
T
n
(πσ*) channel of the BPA molecule and its complex with water. A study of the photolysis of the isolated BPA molecule upon exposure to solar radiation, the short-wavelength boundary of which on the Earth’s surface is located at ~290 nm (~34480 cm
–1
), showed that the energy of the photodissociative state localized on the O–H bond is much higher than this value for BPA. The binding curve is characteristic of the
S
1
(ππ*) state, while the singlet and triplet states of the πσ* type, localized on the single C–C bonds of the central fragment of the molecule, are repulsion curves with a barrier. From our point of view, the low efficiency of the BPA degradation under the influence of solar radiation is due to the presence of a significant potential barrier to the photolysis in the singlet or triplet state. The mechanisms of bond breaking in the BPA + 2
H
2
O
complex are different for the singlet and triplet states, namely, for the
S
3
(πσ*) state, the break occurs by the predissociation mechanism, and for the
T
n
(πσ*) state, due to its population through the singlet-triplet conversion in the
S
1
(ππ*) →
Т
n
(πσ*) channel.
Possible products of merocyanine 540 decay are studied using quantum-chemical calculations. The results of calculation are compared with experimental investigations of the spectral-luminescent ...properties, and the products of photo- and thermodecay of the merocyanine 540 molecule in water are identified. It is shown that different products are formed by thermolysis (decay in the ground electronic state S0) and photolysis (decay in an excited electronic state).
