Substitution effect on molecular packing and transistor performance of indolo [3,2-b]carbazole derivatives

In this manuscript, two chloro-substituted derivatives of indolo[3,2-b]carbazole (ICZ), 2,8-dichloro-indolo[3,2-b]carbazole (CICZ) and 2,8-dichloro-5,11-dihexyl-indolo[3,2-b]carbazole (CHICZ) were designed and synthesized. The only difference between CICZ and CHICZ is at the N-5 and N-11 positions with or without long alkyl side chains. Interestingly, CICZ and CHICZ exhibited similar thermal, optical, and electrochemical properties, while their molecular packing motifs in solid state and corresponding charge transport properties were significantly different. The alkyl chains at N-5 and N-11 positions were proved not only enhancing the solubility and self-organization of the compounds but also shifting the molecular packing from herringbone (CICZ) to one-dimensional pi-pi stacking (CHICZ). Moreover, nearly no field-effect performance was observed for CICZ, while the mobility of CHICZ was as high as 0.14 cm(2) V-1 s(-1) for its thin films and 0.5 cm(2) V-1 s(-1) for its single crystals. These results confirmed that the chemical substitutions are a powerful molecular design tool to tune the molecular packing motifs of organic semiconductors and their corresponding electronic properties.