Photolytic Preparation of Tetrabromothianthrene and Its Transformation to Dinuclear Phthalocyanines

Photolysis of dibromobenzotrithiole (1) and tetrabromodibenzotetrathiocin (4) in CH 2 Cl 2 produced tetrabromothianthrene (2).Compound (2) was treated with CuCN in DMF at 150 °C to give tetracyanothianthrene (5).Dinuclear phthalocyanine (9) was constructed by treatment of a mixture of 5 and dioctoxyphthalonitrile (6) with lithium in n-pentanol.New types of phthalocyanines (Pcs) have been desired to develop advanced functional materials for use with electrochromic displays, field-effect transistors, dye-sensitized solar cells, and so on, which has stimulated the study of the compounds and related functional dyes. 1,2Dinuclear phthalocyanine (DNPc), consisting of two Pcs connected by one or several benzene rings in a peripheral direction, has an enlarged -electronic system. 3The molecules are expected to show redshifts of Q-band absorption and lowering of the oxidation potential compared with mononuclear Pcs.However, it is known that DNPc has low solubility without appropriate substituents because of its planarity and highly aggregative properties.It was reported that DNPc in which two Pcs are linked by two sp 3 carbon atoms has a gable structure and can suppress its aggregation. 4If a 1,4-dithiin ring is introduced between two Pcs instead of the 1,4-cyclohexadiene ring, DNPc could have a wedged form as the two sulfur atoms of the dithiin ring have an sp 3 structure.While the angle between two benzene rings of thianthrene [dibenzodithiin] was reported to be 132°, 5 its conformation could change to planar form by oxidation. 6It was reported that thianthrene derivatives were prepared by the photolysis of dibenzotetrathiocins. 7a We also reported the photolysis of ethylenedithiodiethylbenzotrithiole in CH 2 Cl 2 produced bis(ethylenedithio)-