  We show that the recently synthesized charge-transfer material picene/F4TCNQ
can be used as a gate-voltage controlled molecular switch. The picene/F4TCNQ
system is compared with the extensive characterized anthraquinone-based
molecular system, which is known to exhibit large switching ratios due to
quantum interference effects. In case of picene/F4TCNQ we find switching ratios
larger by one order of magnitude. Further, our calculations reveal that the
picene/F4TCNQ system resembles remarkable well the I-V characteristics of a
classical diode. The reverse-bias current of this molecular diode can be
increased two orders of magnitude by an external gate voltage. Based on
density-functional theory calculations we show that the hybrid states formed by
the picene/F4TCNQ system are playing the key role to determine the transport
properties. We further conclude that the tuning of quantum transport properties
through hybrid states is a general concept which opens a new route towards
functional materials for molecular electronics.
