We investigate the electronic structure of aromatic radical anions in the
solution phase employing a combination of liquid-jet (LJ) photoelectron (PE)
spectroscopy measurements and electronic structure calculations. By using recently
developed protocols, we accurately determine the vertical ionization energies of valence
electrons of both the solvent and the solute molecules. In particular, we first characterize
the pure solvent of tetrahydrofuran (THF) by LJ-PE measurements in conjunction with
ab initio molecular dynamics simulations and G0W0 calculations. Next, we determine
the electronic structure of neutral naphthalene (Np) and benzophenone (Bp) as well as
their radical anion counterparts Np− and Bp− in THF. Wherever feasible, we performed
orbital assignments of the measured PE features of the aromatic radical anions, with
comparisons to UV−vis absorption spectra of the corresponding neutral molecules
being instrumental in rationalizing the assignments. Analysis of the electronic structure
differences between the neutral species and their anionic counterparts provides
understanding of the primarily electrostatic stabilization of the radical anions in solution. Finally, we obtain a very good agreement of
the reduction potentials extracted from the present LJ-PES measurements of Np− and Bp− in THF with previous electrochemical
data from cyclic voltammetry measurements. In this context, we discuss how the choice of solvent holds significant implications for
optimizing conditions for the Birch reduction process, wherein aromatic radical anions play crucial roles as reactive intermediates.