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Publication abstract: Gallic acid (GA) has been characterized in terms of its optical properties in aqueous solutions at varying pH in experiments and in theoretical calculations by analyzing protonated and deprotonated forms of GA. This work is a part of a series of studies of the optical properties of different carboxylic acids in aqueous media. The experimental electronic spectra of GA exhibits two strong well-separated absorption peaks (B- and C-bands), which agrees with previous studies. However, in the current study, an additional well-defined low-energy shoulder band (A-band) in the optical spectra of GA was identified. It is likely that the A-band occurs for other carboxylic acids in solution, but because it can overlap with B-band, it is difficult to discern. The theoretical calculations based on density functional theory were used to simulate optical absorption spectra of GA in water at different pH to prove the existence of this newly founded shoulder band and to describe and characterize full experimental optical spectra of GA. Different cluster models were tested: (i) all water molecules are coordinated near the carboxy-group, and (ii) additional water molecules near the hydroxy-groups of the phenyl ring were included. In this study, we found that both the polarizable continuum model (dielectric property of medium) and neighboring water molecules (hydrogen-bonding) play significant roles in the optical spectrum. Results showed, that only extended cluster-model with water molecules near carboxy- and hydroxy-groups together with polarizable continuum model allowed to fully reproduce the experimental data and captured all three absorption bands (A, B and C). Oscillator strengths of absorption bands were obtained from the experimental data and compared with theoretical results. Additionally, our work provides a detailed interpretation of pH effects observed in the experimental absorption spectra. Research Data Curation Program, UC San Diego, La Jolla, 92093-0175 (https://lib.ucsd.edu/rdcp) Karimova, Natalia, V.; Luo, Man; Sit, Izaac; Grassian, Vicki, H.; Gerber, R., Benny (2022). Data from: Absorption Spectra and Electronic Structure of Gallic Acid in Water at Different pH: Experimental Data and Theoretical Cluster Models. In Center for Aerosol Impacts on Chemistry of the Environment (CAICE). UC San Diego Library Digital Collections. https://doi.org/10.6075/J04J0F85
Optical properties Organic acids Photochemistry chemistry Water clusters Organic chromophores