Wavelength dependent mechanism of phenolate photooxidation in aqueous solution

Phenolate photooxidation is integral to a range of biological processes, yet the mechanism of electron ejection has been disputed. Here, we combine femtosecond transient absorption spectroscopy, liquid-microjet photoelectron spectroscopy and high-level quantum chemistry calculations to investigate the photooxidation dynamics of aqueous phenolate following excitation at a range of wavelengths, from the onset of the S-0-S-1 absorption band to the peak of the S-0-S-2 band. We find that for lambda >= 266 nm, electron ejection occurs from the S-1 state into the continuum associated with the contact pair in which the PhO radical is in its ground electronic state. In contrast, we find that for lambda <= 257 nm, electron ejection also occurs into continua associated with contact pairs containing electronically excited PhO radicals and that these contact pairs have faster recombination times than those containing PhO radicals in their ground electronic state.

Automated summary

We used various spectroscopy techniques and calculations to investigate the photooxidation of aqueous phenolate at different wavelengths. We found that when the wavelength is equal to or larger than 266 nm, electron ejection occurs from the excited state into the continuum associated with the ground state PhO radical. However, when the wavelength is equal to or smaller than 257 nm, electron ejection also occurs into continua associated with electronically excited PhO radicals, which have faster recombination times than the ground state PhO radicals.