Regiochemical Effects of Furan Substitution on the Electronic Properties and Solid-State Structure of Partial Fused-Ring Oligothiophenes

• Published in: Journal of organic chemistry 2012-10, Vol.77 (20), p.9298-9303
• Main Authors: Henssler, John T, Matzger, Adam J
• Format: Article
• Language: English
• Subjects: Chemistry; Electrons; Exact sciences and technology; Furans - chemistry; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Models, Molecular; Molecular Structure; Organic chemistry; Preparations and properties; Stereoisomerism; Thiophenes - chemical synthesis; Thiophenes - chemistry
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo301744s

Oligomers containing the new fused-ring heterocyclic conjugated building block thieno[3,2-b]furan were synthesized, and the effects associated with furan ring substitution into fused-ring oligothiophenes on the electronic properties and solid-state structure were assessed. A series of four-ring oligomers which vary in the degree of furan ring substitution and the regiochemistry of placement were synthesized via Stille cross-coupling and oxidative homocoupling strategies. The electronic properties of these oligomers were studied by UV–vis absorption and fluorescence spectroscopies. Substitution of furan rings at the terminal positions yields oligomers with a narrower HOMO–LUMO gap relative to the all-thiophene analogue 2,2′-bithieno[3,2-b]thiophene, and incorporation of furan rings at the interior positions results in oligomers with an increase in rigidity and a higher fluorescence quantum yield. Packing motifs of the oligomers were determined using single crystal X-ray diffraction. In contrast to the herringbone crystal packing observed for nonfused oligothiophenes, oligofurans, thiophene–furan hybrid oligomers, and the all-thiophene analogue 2,2′-bithieno[3,2-b]thiophene, all three regioisomers derived from the dimerization of thieno[3,2-b]furan arrange in a π-stacked packing motif in the solid state.