  We have designed and synthesized five azulene derivatives containing gold-
binding groups at different points of connectivity within the azulene core to
probe the effects of quantum interference through single-molecule conductance
measurements. We compare conducting paths through the 5-membered ring,
7-membered ring, and across the long axis of azulene. We find that changing the
points of connectivity in the azulene impacts the optical properties (as
determined from UV-Vis absorption spectra) and the conductivity. Importantly,
we show here that simple models cannot be used to predict quantum interference
characteristics of non-alternant hydrocarbons. As an exemplary case, we show
that azulene derivatives that are predicted to exhibit destructive interference
based on widely accepted atom-counting models show a significant conductance at
low biases. Although simple models to predict the low-bias conductance do not
hold with all azulene derivatives, we show that the measured conductance trend
for all molecules studied actually agrees with predictions based on the more
complete GW calculations for model systems.
