New pi-electron donor systems based on acenaphtho[1,2-b][1,4]-dithiine

Syntheses of the acenaphtho[1,2-b] [1,4] dithiine derivatives 12, 25 and 29 are reported. Cyclic voltammetric studies reveal that these compounds undergo reversible single-electron oxidations at < 1.0 V, vs. Ag/AgCl. Lithiation of compound 12 with BuLi (2 equiv.) followed by addition of either methyl iodide or ethyl chloroformate yielded the unstable ring-opened acetylene derivatives 22a and 22b, respectively. A new synthesis of 1,2-diselenine derivative 33 is reported. Compound 25 formed 1:1 charge-transfer complexes with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) and with 2,5-dibromo-TCNQ, both of which were electrical insulators. The X-ray crystal structures of compound 25, a charge-transfer complex 25:Br,TCNQ (1:1 stoichiometry) and compound 33 are reported. In the structure of 25:Br,TCNQ, molecules of 25 and Br,TCNQ form mixed stacks. The folding of the donor along the S ... S vector in the complex is 17 degrees (ef. 48 degrees in pure 25) and the conformation of 25 is discussed in the light of previous studies on 1,4-dithiine derivatives. An interesting feature of the crystal structure of 33 is the formation of pseudo-dimers with two short intermolecular Se Se contacts.