This
paper investigates the electric properties of the photochromic
dihydroazulene/vinylheptafulvene system as it is physisorbed onto
silver and copper nanoparticles. Our focus is on how the polarizability
and hyperpolarizability of the dihydroazulene, s-cis-vinylheptafulvene, and s-trans-vinylheptafulvene
molecules depend on molecular orientation with respect to the nanoparticles,
the molecule–cluster separation, and the type of nanoparticle.
The computational approach utilizes a combined quantum mechanical/molecular
mechanical method in which the molecules are treated quantum mechanically
while the nanoparticles are treated with a simpler classical method.
The molecules are described with density functional theory. The electric
properties are calculated using response theory utilizing the long-range-corrected
functional CAM-B3LYP and the correlation consistent basis set aug-cc-pVDZ.
The atoms of the nanoparticles are represented using atomic polarizabilities.
The interactions between the nanoparticles and the molecular systems
are calculated using a polarizable embedding scheme after which the
molecular properties are calculated with time-dependent density functional
theory. The results show that the electric properties are indeed affected
by the presence of the nanoparticles. It is also clear that it is
the hyperpolarizabilities that change the most while the polarizabilities
are less affected. Furthermore, the influence of the nanoparticles
on the molecules depends heavily on the relative molecular orientation
with respect to the nanoparticles and molecular conformation. Finally,
it is observed that a copper nanoparticle has a larger influence on
the molecular systems than a silver nanoparticle.