Novel Extended Tetrathiafulvalenes Based on Acetylenic Spacers: Synthesis and Electronic Properties

A selection of mono‐ and diacetylenic dithiafulvalenes was synthesized and employed for the construction of extended tetrathiafulvalenes (TTFs) with hexa‐2,4‐diyne‐1,6‐diylidene or deca‐2,4,6,8‐tetrayne‐1,10‐diylidene spacers between the two 1,3‐dithiole rings. By stepwise acetylenic scaffolding using (E)‐1,2‐diethynylethene (DEE) building blocks, an extended TTF containing a total of 18 C(sp) and C(sp2) atoms in the spacer was prepared. The versatility of the acetylenic dithiafulvene modules was also established by the efficient synthesis of a thiophene‐spaced TTF, employing a palladium‐catalyzed cross‐coupling reaction. The developed synthetic protocols allow functionalization of the extended TTFs in three general ways: with 1) peripheral substituents on the fulvalene cores, 2) alkynyl moieties laterally appended to the spacer, and 3) cobalt clusters involving acetylenic moieties. Strong chromophoric properties of the extended TTFs were revealed by linear and nonlinear optical spectroscopies. Extensive electrochemical studies and calculations on these compounds are also reported, as well as X‐ray crystallographic analyses. Extended tetrathiafulvalenes containing varying numbers of acetylene units in the spacer are readily synthesized from mono‐ and diacetylenic dithiafulvene building blocks. These large π‐systems are strong chromophores and exhibit good third‐order nonlinear optical properties. The electrochemical behavior was influenced by both structural changes in the spacer and by lateral functionalization (R′).