Electronic spectra and photolysis of bisphenol a in water

A quantum chemical study of the spectral and luminescent properties of bisphenol A (BPA) and a BPA+2H₂O complex was carried out. The calculations were performed by the semi-empirical method of partial neglect of differential overlap using a complex of programs and special parameterization. The spectral behavior of BPA in water was modeled by a complex with 1: 2 water molecules forming a hydrogen bond. The calculated data were compared with the results of the study of the isolated BPA molecule. The nonplanar structure of the BPA leads to a strong “mixing” of the π- and σ-type atomic wave functions. The main reason for the low quantum yield of BPA fluorescence is the efficient process of singlet-triplet conversion in the channel S ₁(ππ*) ~> T_n (πσ*) in the BPA molecule and complex with water. A study of the photolysis of an isolated BPA molecule under the influence of solar radiation, the short-wavelength boundary of which at the earth’s surface is in the region of ~ 290 nm (~ 34480 cm^-1), showed that the energy of the photo-dissociative 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 single C-C bonds of the central fragment of the molecule, are repulsion curves with a barrier. The low efficiency of the degradation of BPA under the influence of solar radiation, from our point of view, is associated with the presence of a significant potential barrier to the occurrence of photolysis in singlet or triplet states. The mechanisms of bond cleavage in the BPA+2H₂O complex in the singlet and triplet states are different, namely, in the S ₃(πσ*) state, the break occurs according to the predissociation mechanism, and in T_n (πσ*) due to its population through the singlet-triplet conversion during the S ₁(ππ*) → Т_n (πσ*) channel.

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