Synthesis and characterization of <i>S,N</i>-heterotetracenes

Abstract

The synthesis and optoelectronic properties of novel <i>S,N</i>-heterotetracenes consisting of fused heterocyclic thiophene and pyrrole rings are presented. Tetracyclic and benzannulated derivatives with a varying number and sequence of sulfur and nitrogen heteroatoms were synthesized in multistep synthetic routes. A Buchwald-Hartwig amination of brominated precursors, thermolysis of azide precursors, and a Cadogan reaction of nitro-substituted precursors were successfully applied to eventually build-up pyrrole rings to stable and soluble fused systems. The various obtained heteroatom sequences 'SSNS<i>'</i> (SN4), 'SNNS<i>'</i> (SN4''), and 'NSSN<i>'</i> (SN4') allowed for evaluation of structure-property relationships relative to the sulfur analogue tetrathienoacene ('SSSS<i>'</i>). In line with the results for the whole series of <i>S,N</i>-heteroacenes, we find that replacement of sulfur by nitrogen atoms in the tetra- and hexacyclic systems leads to a red-shift in absorption, a decrease in oxidation potential and energy gap. On the other hand, the replacement of a thiophene ring by benzene leads to the opposite effects.