Isomeric diazapyrene-thiophene conjugated systems: synthesis, characterization, and transport properties

Dihalogenated 4,9-diazapyrenes have been shown to be promising reactive intermediates that could be used to develop various diazapyrene-based pi-conjugated systems and have great research prospects. Since pyrene chemistry is strongly position-dependent, two synthesis methods, i.e. post-functionalization (electrophilic substitution) and pre-functionalization (pre-introduction of halogen atoms), were developed to synthesize three dihalogenated diazapyrene molecules substituted at different sites. Then, three isomeric co-oligomers of diazapyrene and bithiophene (1,6-, 2,7- and 3,8-PyNN-T2) were obtained through Suzuki cross-coupling reactions. Their crystal structures, and optoelectronic and charge transport properties were investigated, which demonstrated distinct position-dependence. Among the three isomers, 3,8-PyNN-T2 exhibited hole mobility up to 1.14 cm2 V-1 s-1, as observed in single crystal organic field-effect transistors. Our work fills the gap in the study of halogenated diazapyrenes and provides powerful tools for further derivatization of diazapyrenes.