fig8
Figure 8. Molecular models of BED, BED-T and BED-TT fragments (calculated with DFT/B3LYP/6-31G method). BED-T showed more planar backbone than BED and BED-TT due to the nonbonding. BED: interactions.2,2',3,3'-tetrahydro-5,5'-bithieno[3,4-b][1,4]dioxine; BED-T: 2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)thiophene; BED-TT: 2,5-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)thieno[3,2-b]thiophene.