A post-HF approach to the sunscreen octyl methoxycinnamate

Area of Science:

• Photochemistry
• Computational Chemistry
• Materials Science

Background:

• Octyl methoxycinnamate (OMC), also known as octinoxate, is a widely used UVB filter in sunscreens.
• OMC is prone to photodegradation, where its efficacy as a UVB filter diminishes.
• The trans (E) isomer of OMC converts to the cis (Z) isomer upon light exposure, impacting its stability.

Purpose of the Study:

• To investigate the relative stability of the cis (Z) and trans (E) isomers of octyl methoxycinnamate (OMC) in the gas phase.
• To evaluate the accuracy of different computational methods in predicting the stability of OMC isomers.
• To elucidate the stabilizing factors for the cis isomer of OMC.

Main Methods:

• Utilized post-Hartree-Fock methods, including coupled cluster approaches (CCSD, CCSD(t), and CCSD + T(CCSD)).
• Optimized ground-state geometries of OMC using the MP2 level of theory.
• Employed dispersion-corrected density functional theory (DFT) methods, specifically the B2PLYP double hybrid functional, for comparative analysis.

Main Results:

• Post-Hartree-Fock calculations indicate comparable stability between the cis and trans isomers of gas-phase OMC.
• Dispersion-corrected DFT methods, including B2PLYP, incorrectly predict the trans isomer to be more stable.
• The study reveals that intramolecular dispersion interactions stabilize the cis-OMC isomer, leading to a more compact structure.

Conclusions:

• The cis isomer of OMC possesses comparable stability to the trans isomer, contrary to previous assumptions.
• Advanced computational methods like coupled cluster are necessary to accurately capture the subtle stabilization of the cis isomer.
• Intramolecular dispersion forces play a crucial role in the stabilization of the cis-OMC isomer, impacting its photochemical behavior.