| Abstract
| - Monodisperse and polydisperse oligomers of benzo[1,2-b:4,3-b‘]dithiophene (BDT) (1−14), includingthree types of oligomers with different spacers combining BDT units (direct linkage, vinylene spacers,and ethynylene spacers), were synthesized, and their thermal, optical, and electrochemical propertieswere investigated. The oligomers were synthesized using Suzuki, Stille, Wittig, and Sonogashira couplingreactions. All of the monodisperse oligomers showed high melting points and 5% weight loss temperatures(Td> 400 °C). The fluorescence maxima of all oligomers were red-shifted, and the emission colorsvaried from blue to yellow as the chain lengthsand thus the conjugation lengthsincreased. The vinylene-bridged oligomers emitted at longer wavelengths than the direct-linked and ethynylene-bridged oligomers.UV−vis absorption spectra in toluene solution indicated an effective conjugation length of about sixBDT units for polydisperse oligomer 5. Cyclic voltammetry measurement indicated that tetramer 3 hadhigh electrochemical stability. Although tetramer 3 and vinylene-bridged tetramer 8 exhibited reversibleoxidation waves, ethynylene-bridged tetramer 13 showed an irreversible oxidation process. Each type ofmonodisperse oligomer exhibited higher HOMO levels with increasing chain length.
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