UV filter 2-ethylhexyl 4-methoxycinnamate: a structure, energetic and UV-vis spectral analysis based on density functional theory

摘要

2-Ethylhexyl 4-methoxycinnamate (EHMC) is a very commonly used UVB filter that is known to isomerize from the (E) to the (Z) isomer in the presence of light. In this study, we have performed high level quantum chemical calculations using density functional theory (DFT) with the B3LYP density functional and extended basis sets to study the gas-phase molecular structure of EHMC and its energetic stability. Calculations were also performed for related smaller molecules cinnamic acid and 4-methoxycinnamic acid. Charge delocalization has been analyzed using natural charges and Wiberg bond indexes within the natural bond orbital analysis and using nucleus independent chemical shifts. Density functional theory calculations reveal that the (E) isomer of EHMC is more stable than the (Z) by about 20kJmol~(-1) in both the gas and aqueous phases. The enthalpy of formation in the gas phase of (E)-EHMC was derived from an isodesmic bond separation reaction. Long-range corrected DFT calculations in implicit water were made in order to understand the excited state properties of the (E) and (Z) isomers of EHMC.