Exploring Autoionization and Photoinduced Proton-Coupled Electron Transfer Pathways of Phenol in Aqueous Solution

Abstract

The excited state dynamics of phenol in water have been investigated using transient absorption spectroscopy. Solvated electrons and vibrationally cold phenoxyl radicals are observed upon 200 nm and 267 nm excitation, but with formation timescales that differ by more than four orders of magnitude. The impact of these findings is assessed in terms of the relative importance of autoionization versus proton-coupled electron transfer mechanisms in this computationally tractable model system. TOC GRAPHIC

Beyond esterase‐like activity of serum albumin. Histidine‐(nitro)phenol radical formation in conversion cascade of p‐nitrophenyl acetate and the role of infrared light

“…In fact, a detailed inspection of the spectral signatures evolving in our experimental system suggests formation of phenoxyl radical (Figure ). Its presence is marked by characteristic pair of the UV–Vis peaks of similar intensity located around 386 and 406 nm. It has been stated previously that 386‐nm peak belongs to the spectral fingerprint of the HNO 2 .…”

Solvent reorganization triggers photo-induced solvated electron generation in phenol

“…In contrast, upon excitation of the bright pp* state at 267 nm the signals of solvated electrons and phenoxyl radicals begin to rise after about 2 ns. 47 In this case, no signal corresponding to the intermediate PhOH + was observed, which the authors attributed to the short lifetime of this species. 47 However, the absence of the signal may also indicate that the intermediate is not formed and that the proton and the electron are transferred to the solvent in a concerted way.…”

“…47 In this case, no signal corresponding to the intermediate PhOH + was observed, which the authors attributed to the short lifetime of this species. 47 However, the absence of the signal may also indicate that the intermediate is not formed and that the proton and the electron are transferred to the solvent in a concerted way. Additional experiments on deuterated phenol (phenol-d 1 ) 47 at 267 nm revealed only a small kinetic isotope effect of 1.0 AE 0.4, thus indicating that proton transfer is not the rate-limiting step of the reaction in solution.…”

“…Experimental studies in the gas phase, [26][27][28][29][30][31][32][33] as well as in the apolar aprotic solvent cyclohexane, 46 support the mechanism of photodissociation by an O-H elongation, without electron transfer to the solvent (as the latter do not exist or no polar protic solvent is available). In aqueous solution, evidence for a photodissociation mechanism different from gas-phase phenol was recently found by Oliver et al 47 using transient absorption spectroscopy. After excitation with 200 nm light, solvated electrons and phenoxyl radicals PhO were observed within 200 fs.…”

“…47 However, the absence of the signal may also indicate that the intermediate is not formed and that the proton and the electron are transferred to the solvent in a concerted way. Additional experiments on deuterated phenol (phenol-d 1 ) 47 at 267 nm revealed only a small kinetic isotope effect of 1.0 AE 0.4, thus indicating that proton transfer is not the rate-limiting step of the reaction in solution. However, this conclusion stands only if proton transfer is dominated by tunneling effects.…”