Oxidative Bond Formation in Dithienyl Polyphenylenes: Optical and Electrochemical Consequences

A new set of dithienyl polyphenylenes was prepared with a view of developing sulfur‐containing polyaromatic hydrocarbons (PAHs) by oxidative cyclodehydrogenation. The first of these, 1,2‐bis(5‐methyl‐2‐thienyl)‐3,4,5,6‐tetra‐(4‐tert‐butylphenyl)benzene (1) was sterically hindered at the 5‐positions of the thienyl rings and under Lewis acid catalyzed cyclodehydrogenation gave monomeric intramolecularly fused dithienyl 3, which was spectroscopically and structurally characterized. Under the same conditions, three unhindered dithienyl polyphenylenes, 1,2‐(thienyl)‐3,4,5,6‐tetra(4‐tert‐butylphenyl)s 2, 5, and 6, underwent both thiophene‐directed intra‐ and intermolecular C–C bond fusions. The resulting dimers 4, 7, and 8 were identified through a series of 1H, 13C, and 2D NMR experiments. The electrochemical and photophysical properties of the dimers were examined. Their optical properties reflect the coplanarity or otherwise of their cojoined parts. The electrochemical oxidation of the dithienyl polyphenylene precursors showed a relationship between the ease of oxidation and the availability of the 2‐ and 5‐positions on the thienyl rings. Using spectroelectrochemical methods the electrochemically oxidized and chemically oxidized products were compared.