  Structure-function relationships constitute an important tool to investigate
the fundamental principles of molecular electronics. Most commonly, this
involves identifying a potentially important molecular structural element,
followed by designing and synthesizing a set of related organic molecules, and
finally interpretation of their experimental and/or computational quantum
transport properties in the light of this structural element. Though this has
been extremely powerful in many instances, we demonstrate here the common need
for more nuanced relationships even for relatively simple structures, using
both experimental and computational results for a series of stilbene
derivatives as a case study. In particular, we show that the presence of
multiple competing and subtle structural factors can combine in unexpected ways
to control quantum transport in these molecules. Our results clarify the
reasons for previous widely varying and often contradictory reports on
charge-transport in stilbene derivatives, and highlight the need for refined
multidimensional structure-property relationships in single molecule
electronics.
