Synthesis and Properties of a Series of Well-Defined and Polydisperse Benzo[1,2-b:4,3-b‘]dithiophene Oligomers

Monodisperse and polydisperse oligomers of benzo[1,2-b:4,3-b‘]dithiophene (BDT) (1−14), including three types of oligomers with different spacers combining BDT units (direct linkage, vinylene spacers, and ethynylene spacers), were synthesized, and their thermal, optical, and electrochemical properties were investigated. The oligomers were synthesized using Suzuki, Stille, Wittig, and Sonogashira coupling reactions. 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 colors varied 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 six BDT units for polydisperse oligomer 5. Cyclic voltammetry measurement indicated that tetramer 3 had h...