A new approach to the synthesis of fused benzothiophene derivatives was developed based on iodine-promoted photo-cyclization of 4,5-diarylsubstituted thiophenes obtained in three steps from commercially available compounds. Comparative analysis showed that photochemical cyclization is a more efficient method for the preparation of fused benzo[b]thiophene derivatives, compared to oxidative coupling 4,5-diarylsubstituted thiophenes in the presence of iron (III) chloride and palladium catalyzed intramolecular arylation. This approach provides an efficient synthesis of functionally substituted naphtho[2,1-b: 3,4-b ']dithiophenes, phenanthro[9,10-b] thiophenes, benzo[1,2-b: 3,4-b': 6 , 5-b '']trithiophenes, as well as new fused heterocycles containing a pyridine ring and / or a carbazole moiety

symmetrically disubstituted with 3-alkyl-(2,2′-bithiophen)-5-yl were synthesized by new procedures using readily available ethyl 3-alkyl-(2,2′-bithiophene)-5carboxylate as a convenient substrate. These new compounds with a fixed number of donor rings and increasing number of acceptor rings showed very interesting, tunable redox properties. In particular, they exhibited electron affinities (EAs) ranging from −3.06 to −3.83 eV, reaching EA values desired for air-operating n-type organic semiconductors. Their electrochemically determined ionization potentials were only moderately dependent on the number of thiadiazole rings, varying from 5.83 to 6.01 eV. Emission spectra of these compounds could also be tuned in a wide range (from 470 to 600 nm). Spectroscopic and electrochemical data were confirmed by density functional theory calculations demonstrating full consistency.

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