Charge transport properties of stacking bisindenoanthrazolines: DFT studies

Organic semiconductors to date having cofacial stacking motif are scarce compared to those having herringbone motif. Recently, Ahmed and co-workers have reported a series of novel n-type bisindenoanthrazolines (BIDAs) [Chem. Mater. 2010, 22, 5786], among which DADF and DADK adopt different slipped cofacial arrangements exhibiting distinct electron transport abilities. Here, we performed computational studies to understand the relationship between charge transport and molecular packing for these BIDAs molecules. This work focuses on the intrinsic molecular factors required for efficient and long-range charge transfer. Unlike the previous studies only focusing the charge injection barriers or the carrier mobilities, herein, we present the notion that lower electron injection barrier and higher intrinsic electron mobility should be both satisfied to achieve better n-type OFETs. We also note that the actual mobility can be significantly underestimated due to the limitation of the space-charge limited current method. Through computational modeling, we rationalized the superior electron conductivity of DADK and also shed light on the favorable or undesirable properties for efficient charge transport of BIDAs. Another key finding is that the intrinsic electron and hole mobilities are quite deviated from each other rather than comparable in current mobility calculations.