Improved stability in N-alkylated organic semiconductors for thin film transistors: Synthesis and characterization of N,N′-dialkylated dihydrodiazapentacene derivatives

We have successfully synthesized and characterized newly designed oxidation-resistant N,N′-dialkylated dihydrodiazapentacene (1a: alkyl = hexyl) and (1b: alkyl = stearyl) as stable semiconductor materials under ambient conditions for organic field-effect transistors (OFETs). The crystal structure analysis has allowed us to know that 1a has a face-to-face slipped π–π stacking motif, with the intermolecular distance being about 3.49 Å, which forms a one-dimensional column. XRD and AFM measurements reveal that the vacuum deposited films of 1a and 1b are similar crystalline phases with molecules being tilted from the substrate plane. The OFETs fabricated using 1a and 1b exhibit typical p-type FET performances with mobilities of 3.2 × 10−3 and 3.0 × 10−5 cm2 V−1 s−1, respectively. The storage tests of OFETs using 1a in the presence of air for 3 months have proven high device stability with no significant changes in mobilities and on/off ratios. The relatively low mobilities can be attributed to the undesirable overlap of HOMOs and the strongly anisotropic one-dimensional π–π stacking.