Synthesis and optical properties of conjugated N, N-dimethyl and thienyl end-capped 2,5-(arylethynyl)thiophene oligomer structures

Abstract

End-capped ( N, N-dimethylaminophenyl) and 2′-thienylethynyl 2,5-thiophene oligomer structures were synthesized by heterocoupling between the terminal acetylenes such as: p-( N, N-dimethylaminophenyl)ethyne (3) [or 1-( p-( N, N-dimethylaminophenyl)-2- p-(ethynylphenyl)ethyne, 4]; p-(β-ethenyl-2′-thienyl)phenylethyne ( E-9) [or p-(β-ethynyl-2′-thienyl)phenylethyne, 11], and 2,5-diiodothiophene, catalyzed by the Cl 2Pd(PPh 3) 2/CuI system, in good to excellent yields. The 2,5-di[(3′,5′-di(trimethylsilylethynyl)phenyl] x -1-ethynyl]thiophene oligomers were prepared by heterocoupling between 3′,5′-di[(trimethylsilylethynyl)phenyl] x -1-ethyne ( n = 0–2) terminal acetylenes and 2,5-diiodothiophene, in excellent yields. The terminal acetylenes were efficiently prepared by a specific protection-deprotection methodology. All the ethynylphenyl compounds obtained show fluorescence radiation emission, with a bathochromic shift of the wavelength that increases with the chain conjugation.