Metal salen coordination compounds: A new type of ambipolar charge transport materials

A series of metal (Ni or Cu) salen coordination compounds were designed, synthesized and characterized. Their photophysical properties, electrochemical properties and thin film morphologies were studied. Their charge transport properties were measured by time of flight (TOF) technique. Compounds 1a and 1b showed hole transport properties, while compounds 2 and 3 exhibited balanced ambipolar mobilities. DFT calculation results were in good agreement with the experimental results and provided an explanation for the unexpected TOF results. Compound 3 showed the highest mobilities (10−5 cm2/Vs) for both holes and electrons at ambient temperature, suggesting a promising candidate of ambipolar charge transport materials.