Atmospheric persistence and toxicity evolution for fluorinated biphenylethyne liquid crystal monomers unveiled by in silico methods.

It is essential to understand the atmospheric fate of liquid crystal monomers (LCMs), an important component in liquid crystal displays (LCDs); however, limited information is available at present. In this study, the atmospheric reaction mechanism, kinetics and toxicity evolution of three fluorinated biphenylethyne LCMs (1,2,3-trifluoro-5-(2-(4-methylphenyl)ethynyl)benzene (m-TEB), 1,2,3-trifluoro-5-(2-(4-ethylphenyl)ethynyl)benzene (e-TEB), 1,2,3-trifluoro-5-(2-(4-propylphenyl)ethynyl)benzene (p-TEB)) are investigated by theoretical calculations. Results show that the initial reactions of·OH addition to -C ≡ C- groups and hydrogen abstraction from alkyl groups (-CH3, -C2H5, -C3H7) are dominant pathways. The resulting transformation products (TPs) for m-TEB are mainly highly oxidized multi-functional compounds such as benzil-based compounds, benzoic acid, alcohols, aldehydes, diketone and epoxy compounds. Results also show that some TPs exhibit higher aquatic toxicity than the parent. The calculated rate constants of m-TEB, e-TEB and p-TEB with·OH at 298 K are in the ranges of (1.3 -8.6) × 10-12 cm3 molecule-1 s-1, and the corresponding atmospheric half-lives are 3.8-9.3, 2.2-5.4 and 0.6-1.4 days, respectively. This evidences that m-TEB and e-TEB may have atmospheric persistence and could undergo long-range transport. The results herein could be helpful for clarifying the atmospheric fates, persistence and risks of fluorinated LCMs with ethynyl benzene center.