calculations, nitrobenzene was optimized on the S0 surface
using the CAM-B3LYP70 (link)/Def2-TZVP71 (link) method
employing empirical dispersion with Becke–Johnson damping (GD3BJ).72 (link) The analysis of the vibrational frequencies
confirmed this geometry as a minimum. Molecules of each solvent system
were positioned by hand around the nitrobenzene molecule to maximize
interactions with the NO2 group, and the resulting microsolvated
system was reoptimized at the CAM-B3LYP/Def2-SVP level of theory.
The analysis of the vibrational frequencies again confirmed the resulting
microsolvated systems as minima. These calculations were performed
using the Gaussian 16 program.73 Following our earlier work,29 (link) all excited-state
calculations on the various gas-phase nitrobenzene structures were
performed at the CASPT2 level, with the same CAS(14,11) active space
as before, which includes the π-orbitals on the ring and the
lone pairs on the nitro-oxygen atoms.29 (link) The basis set was the atomic natural orbital (ANO) of S-type double-ζ
with polarization (ANO-S-VDZP).74 (link) The geometries
were taken from our earlier work29 (link) and
calculations were performed using the OpenMolcas program 2023.75 (link) The CASSCF wave functions were state averaged
over 6 singlets and 5 triplets, except for the triplet excitations
from the T1(nAπ*) and T2(πOπ*) minima which included 7 triplet states. Solvation
effects were included using a water PCM, with the equilibrium charges
from the ground state used for nonequilibrium PCM calculations of
the excited states. Structure optimizations were all at the CASSCF
level.