Tuning Thiophene with phosphorus: Synthesis and electronic properties of benzobisthiaphospholes

1,4-Dimercapto-2,5-diphosphinobenzene and 3,6-bis(hexyloxy)-1,4-dimercapto- 2,5-diphosphinobenzene were synthesized and combined with various acid chlorides to obtain a series of benzobisthiaphospholes. Electrochemical and photophysical properties of the substituted benzobisthiaphospholes have been evaluated, and the observed reductions are more facile than the related benzothiaphospholes and 2,6-diphenylbenzobisthiazole. A benzobisthiaphosphole with C₆H ₄-p-CN substituents was reduced at E_1/2=-1.08 V (vs. saturated calomel electrode (SCE)). X-ray diffraction data for several of these phosphorus heterocycles has been obtained, and DFT calculations at the B3LYP level have been performed. Fused-ring systems: Energetic tuning of conjugated building blocks can be achieved by atomic modulation of aromatic architectures. A phosphorus mimic of benzodithiophene and benzobisthiazole has been synthesized and structurally characterized (see figure). The UV/Vis spectrum of the phosphorus heterocycle is significantly redshifted compared to its organic counterparts. The redox properties of the benzobisthiaphospholes have been probed and revealed reversible reductions in THF.