Heteroheptacenes with fused thiophene and pyrrole rings.

The preparation of conjugated heteroheptacenes using an electrophilic coupling reaction induced by a super acid is reported. The new molecules containing thiophene and/or pyrrole rings are bisbenzo[b,b']thienodithieno[3,2-b:2',3'-d]pyrrole, bisbenzo[b,b']thienocyclopenta[2,1-b:3,4-b']dithiophene, and bisthieno[3,2-b]thieno[2,3-f:5,4-f']carbazole. Dithieno[3,2-b:2',3'-d]pyrrole, cyclopenta[2,1-b:3,4-b']dithiophene, and carbazole are used as the aromatic cores. This versatility provides access to molecules with systematically controllable physicochemical properties. Single-crystal X-ray analyses demonstrate that the type and position of the alkyl substituents significantly changes the packing properties of the new molecules. The optical and optoelectronic properties of the heteroheptacenes vary considerably depending on the number and position of the sulfur or nitrogen linkages and reveal the improved environmental stability over their hydrocarbon counterparts. The analysis of the experimental results from UV/Vis absorption/photoluminescence (PL) spectroscopy and cyclic voltammetry were combined with DFT quantum-chemical calculations and compared with other model heteroheptacenes. The results suggest that among the acenes with the same number of fused rings, the thiophene ring fusion inside the skeleton stabilizes both HOMO and LUMO levels more effectively than pyrrole and benzene rings. The present study also shows that the new heteroheptacenes are promising candidates for the construction of electronic materials.