Charge Transfer and Delocalization in Ladder-Type Fused Bithiophene Imide Oligomers - zeng's paper

On the basis of experimentally reported series of novel imidefunctionalized ladder-type heteroarenes (fused bithiophene imide oligomers BTIn, n = 1−5), expanded BTIn up to 24 rings with 8 imide groups (n = 6− 8) as well as some heteroarenes derived from BTI are designed. Charge transfer and delocalization properties of BTIn (n = 1−8) are studied theoretically by non-empirically optimal tuned range-separated density functional theory (DFT) (LC-BLYP*), LC-BLYP* combining polarizable continuum model (PCM) [LC-BLYP* (PCM, solid)], and traditional B3LYP functional. LC-BLYP* provides a good balance between localized and delocalized effects and reduces the electron self-interaction error of the traditional DFT method, whereas combining PCM model with tuned rangeseparated DFT could accurately describe the properties of single crystals. The relationships between geometries, electronic properties, and semiconductor performances are explored. Because of the good planarity induced by the fused thienothiophene rings with the imide, BTI oligomers show better performance than their derivatives with a similar number of thiophene rings. It was found that the BTI oligomers have very good planarity, large conjugation extent, fully delocalized polaron (over 16T units), and good semiconductor properties for both p- and n-types. BTI8 is good potential ambipolar semiconductor with a very small chargeinjection barrier and large hole and electron mobilities of 16.60 and 3.02 cm2 V−1 s−1, respectively. Different roles of thiophene and imide rings in making BTI series a good semiconductor are also revealed by comparing BTI2 and BTI3 with thiophenecontaining derivatives.