Inter- and Intramolecular Interactions in Some Bromo- and Tricyanovinyl-Substituted Thiophenes and Ethylenedioxythiophenes

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···Br Interactions of less than 3.5 Å appear to be dominant in the crystal structures of the dibromo EDOT molecules and yet are almost nonexistent in 5,5″-dibromoterthiophene (shortest Br···Br distances are >4.2 Å), indicating a cooperative role involving the Br and the ethylenedioxy moiety. Short Br···Br distances of 3.5 Å 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···N (3.03 Å) intermolecular interactions in TCV-EDOT are replaced by competing N···Br (2.99 Å) interactions. Short intramolecular N···S distances ranging from 3.2 to 3.3 Å 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 Å) and C–C (1.37–1.44 Å) within the thiophene rings. These findings suggest that N···S, N···Br, and Br···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 π-stack formation patterns.