Synthesis and basic properties of tetrathieno[2,3-a:3′,2′-c:2″,3″-f:3‴,2‴-h]naphthalene: a new π-conjugated system obtained by photoinduced electrocyclization–dehydrogenation reactions of tetra(3-thienyl)ethene

A method for the synthesis of tetrathieno[2,3-a:3′,2′-c:2″,3″-f:3‴,2‴-h]naphthalene (3), utilizing photoinduced electrocyclization–dehydrogenation reactions of tetra(3-thienyl)ethene (1), was developed. Photoirradiation of a toluene or CHCl3 solution of 1, containing a small amount of I2, leads to modestly efficient production of 3. In contrast to the UV–vis absorption property of the typical p-type organic transistor material pentacene, that of 3 does not experience a time-dependent change under aerated conditions, indicating that 3 has high stability against molecular oxygen. The results of X-ray crystallographic analysis demonstrate that 3 possesses a columnar crystalline structure in which molecules are aligned in a face-to-face manner with a high degree of the π–π overlap between adjacent molecules. This phenomenon should result in efficient charge-carrier transport properties of the crystalline form of this substance.