EFFECT OF SOLVENT ON PHOTOCHEMICAL PROPERTIES OF POLYCYCLIC AROMATIC HYDROCARBONS: A DFT STUDY

摘要

Excited state properties of polycyclic aromatic hydrocarbons (PAHs) are important for understanding their photodegradation processes. Density functional theory (DFT) was employed to investigate the photochemical properties of representative PAHs, including phenanthrene (PHE), pyrene (PYR) and benzo[a]pyrene (BaP), dissolved in methanol, ethanol, acetone, acetonitrile, dimethylsulfoxide (DMSO), cyclohexane, dichloromethane (DCM) and water. The lowest singlet excitation energy (ES1), lowest triplet excitation energy (ET1), and vertical ionization potential at the lowest excited triplet (VIPT1) of the PAHs in the different solvents were computed. The results showed that there was no significant difference among the ES1 and the ET1 values for the three PAHs. However, VIPT1 values were affected by the different solvents, ranging from 3.10 eV to 3.97 eV for PHE, 3.30 eV to 4.13 eV for PYR, and 3.40 eV to 4.16 eV for BaP. Correlation analysis showed that VIPT1 decreased with increasing the dielectric constants ( ε) of the solvents. The results implied that the solvent with large ε value facilitated the electron transferring of excited state PAHs and hence the photolysis of PAHs.