Water assisted photo-oxidation from hydroquinone to p-benzoquinone in a solid Ne matrix

Photochemistry of molecular complexes of hydroquinone (HQ) with water, HQ–(water)n, were investigated by matrix-isolation FTIR spectroscopy with aids of density functional theory (DFT) calculations. The HQ monomer did not show any photo-reactivity at 350 nm but was photolyzed at 300 nm. The HQ–(water)n complex was found to be chemically transformed into p-benzoquinone (BQ)–(water)n with the 350 nm irradiation. The experimental threshold wavelength is almost comparable to the S1–S0 transition energy of HQ–(water)2 estimated by a time-dependent DFT calculation. The observation indicates that two water molecules make electron-donated hydrogen-bonds with HQ and assist the photooxidation of HQ to BQ.

► The UV photoreaction product from HQ–(water)n (n ≥ 2) isolated in a Ne matrix was identified as BQ–(water)n by IR spectroscopy with aids of DFT calculations.
► The S1–S0 transition wavelength, 358 nm, calculated for HQ–(water)2 complex is consistent with the experimental threshold wavelength, 350 nm, measured for the photoreaction from HQ–(water)n to BQ.
► This is the first report on the photochemistry of HQ–(water)n.