Two series of dicyanovinyl-substituted compounds namely 2-aryl-5dicyanovinyl-thiophenes 4 and 5-aryl-5´-dicyanovinyl-2,2´-bithiophenes 6 were synthesized through Knoevenagel condensation of the corresponding 2-aryl-5-formylthiophenes 3 and 5-aryl-5´-formyl-2,2´-bithiophene 5 precursors. On the other hand, precursors 3 were prepared through the Vilsmeier-Haack-Arnold reaction (VHA) starting from inexpensive and easily available precursors such as acetophenones. This method produced the title compounds in higher yields than the recently reported synthesis via Suzuki coupling of functionalized aryl boronic acids with 5-bromo-2formyl-thiophene. Electrochemical studies and characterization of the optical (linear and nonlinear), and thermal properties for compounds 5-6 indicate that, good nonlinearity is complemented by exceptional thermal stability for chromophores 6, making them potential candidates for several optoelectronic applications such as solvatochromic probes and nonlinear optical materials.
Photophysical and TPA properties of series of push-pull aryl(bi)thiophene chromophores bearing electron-donating (D) and electron-withdrawing (A) end-groups of increasing strength are presented. All compounds show an intense intramolecular charge transfer (ICT) absorption band in the visible region. Increasing the D and/or A strength as well as the length of the conjugated path induces bathochromic and hyperchromic shifts of the absorption band as reported for analogous push-pull polyenes. Yet, in contrast with corresponding push-pull polyenes, a significant increase in fluorescence is observed. In particular, chromophores built from a phenyl-bithienyl conjugated path and bearing strong D and A end-groups were found to combine very large one and two-photon brightness as well as strong emission in the red/NIR region. These molecules hold promise as biphotonic fluorescent probes for bioimaging.
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