Abstract
We report herein on the competing inter- and intramolecular interactions in seven structurally related thiophene and ethyelenedioxythiophene (EDOT) molecules, substituted with bromine and/or tricyanovinyl (TCV) groups in various combinations, using single crystal structural analyses. Br center dot center dot center dot Br Interactions of less than 3.5 angstrom appear to be dominant in the crystal structures of the dibromo EDOT molecules and yet are almost nonexistent in 5,5 ''-dibromoterthiophene (shortest Br center dot center dot center dot Br distances are >4.2 angstrom), indicating a cooperative role involving the Br and the ethylenedioxy moiety. Short Br center dot center dot center dot Br distances of 3.5 angstrom within stacks and between adjacent stacks of molecules in crystalline dibromo EDOT dimer (6) could be utilized for the preparation of highly ordered polymers with the perfectly planar EDOT dimer as repeating unit, similar to the work reported by Wudl.(18) On the other hand, new dimeric motifs are formed in Br-EDOT-TCV as strong S center dot center dot center dot N (3.03 angstrom) intermolecular interactions in TCV-EDOT are replaced by competing N center dot center dot center dot Br (2.99 angstrom) interactions. Short intramolecular N center dot center dot center dot S distances ranging from 3.2 to 3.3 angstrom are associated with small dihedral angles between the TCV and thiophene planes ranging from 0.80 to 4.3 deg. A slight enhancement of molecular planarity apparently has a profound impact on the extent of conjugation as evident from the C=C bond lengths (1.34-1.40 angstrom) and C-C (1.37-1.44 angstrom) within the thiophene rings. These findings suggest that N center dot center dot center dot S, N center dot center dot center dot Br, and Br center dot center dot center dot Br inter- and intramolecular interactions could be utilized as additional crystal engineering tools to promote molecular planarity and arrangement of higher oligomers in the solid state prior to polymerization of thiophene-based molecular materials. On the basis of the current study, these interactions appear to also enhance the stability of the structure and influence intramolecular charge transfer and pi-stack formation patterns.