  An optimized direct arylation polycondensation (DAP) protocol for the
synthesis of a novel naphthalene diimide (NDI) 2,2'-bithiazole (2-BTz)
copolymer (PNDI-2-BTz) is presented. The regioselective C-H activation of 2-BTz
at the 5-positions allows for the synthesis of fully regioregular and
homocoupling-free PNDI-2-BTz of high molecular weight in less than 1 h in
quantitative yield. Complete end group assignment shows functionalities
according to monomer structures or to nucleophilic substitution, and allows for
the reliable determination of absolute molecular weight. Compared to the
well-known bithiophene analog PNDIT2, an exceptionally high thermal stability,
a hypsochromically shifted charge transfer absorption band and a lower-lying
LUMO energy level is found, making PNDI-2-BTz an interesting candidate for
applications in organic electronic devices. In contrast to the selective and
high yielding C-H activation of 2-BTz at the 5-position, the regioisomer
5,5'-bithiazole is inactive under a variety of conditions.
