Synthesis and characterization of novel, thermally stable 2-aryl-5-dicyanovinylthiophenes and 5-aryl-5′-dicyanovinyl-2,2′-bithiophenes as potentially promising non-linear optical materials

Two series of dicyanovinyl-substituted compounds namely 2-aryl-5-dicyanovinylthiophenes and 5-aryl-5′-dicyanovinyl-2,2′-bithiophenes were synthesized through Knoevenagel condensation of the corresponding 2-aryl-5-formyl-thiophenes and 5-aryl-5′-formyl-2,2′-bithiophene precursors. In contrast, the 2-aryl-5-formyl-thiophenes precursor were prepared through the Vilsmeier–Haack–Arnold reaction starting from inexpensive and easily available precursors such as acetophenones; this method produced the title compounds in higher yield than that recently reported which involved the Suzuki coupling of functionalized aryl boronic acids with 5-bromo-2-formyl-thiophene. Electrochemical studies and characterization of both the linear and non-linear optical properties and thermal properties indicated that good non-linearity was complemented by exceptional thermal stability for some chromophores, making them potential candidates for several optoelectronic applications such as solvatochromic probes and non-linear optical materials.