Substituent Effects on the Photochemistry of Aqueous Phenolate-Based Anions Revealed by Extreme Ultraviolet Time-Resolved Photoelectron Spectroscopy
Year: 2026
Type: preprint
Abstract: Phenolate (PhO-) is a prototypical chromophore and a recurring motif in photoactive biomolecular systems. Here, we use extreme-ultraviolet time-resolved photoelectron spectroscopy (XUV-TRPES) to probe how para-substitution redirects the photophysics of aqueous 4-nitrophenolate (4NP-) and 4-chlorophenolate (4CP-) anions. In 4NP-, following 400 nm excitation, internal charge reorganization accompanied by nitrogroup torsion forms a stabilized twisted intramolecular charge-transfer (TICT) configuration in 74 fs, efficiently funneling the population through a conical intersection to the ground state within 200 fs. Similar dynamics are seen upon excitation at 240 nm, although the initially excited state is even shorter-lived (40 fs). No hydrated electron production is seen at either wavelength. In 4CP-, following 240 nm excitation of the S2 state, internal conversion to S1 occurs within 120 fs. Chlorine substitution introduces a competing 1πσ* dissociative channel whose potential energy surface intersects S1, but the higher S1/1πσ* crossing barrier relative to 4BP- allows the S1 population to survive long enough (25 ps) for solvent-assisted electron ejection and internal conversion. The dynamics thus resemble those of PhO- rather than the sub-picosecond dissociative relaxation of 4BP-. Taken together with our previous PhO- and 4-bromophenolate (4BP-) measurements, these results reveal how para-substitution across this prototypical series drives the accessibility of competing excited-state dynamical processes, leading to very different photostability and photochemistry.
Source: ChemRxiv
Language: English
Subfield: Physical and Theoretical Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221697970