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

摘要

Oligomers containing the new fused-ring heterocyclic conjugatednbuilding block thieno[3,2-b]furan were synthesized, and the effects associated withnfuran ring substitution into fused-ring oligothiophenes on the electronic propertiesnand solid-state structure were assessed. A series of four-ring oligomers which vary innthe degree of furan ring substitution and the regiochemistry of placement werensynthesized via Stille cross-coupling and oxidative homocoupling strategies. Thenelectronic properties of these oligomers were studied by UV−vis absorption andnfluorescence spectroscopies. Substitution of furan rings at the terminal positionsnyields oligomers with a narrower HOMO−LUMO gap relative to the all-thiophenenanalogue 2,2′-bithieno[3,2-b]thiophene, and incorporation of furan rings at theninterior positions results in oligomers with an increase in rigidity and a highernfluorescence quantum yield. Packing motifs of the oligomers were determined usingnsingle crystal X-ray diffraction. In contrast to the herringbone crystal packingnobserved for nonfused oligothiophenes, oligofurans, thiophene−furan hybrid oligomers, and the all-thiophene analogue 2,2′-nbithieno[3,2-b]thiophene, all three regioisomers derived from the dimerization of thieno[3,2-b]furan arrange in a π-stackednpacking motif in the solid state.