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 extensively characterized anthraquinone-based molecular system, which is known to exhibit large switching ratios due to quantum interference effects. In the case of picene-F₄TCNQ we find switching ratios larger by one order of magnitude. Further, our calculations reveal that the picene-F₄TCNQ system resembles remarkably 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 play the key role in determining 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.