Linear Heterocyclic Aromatic Fluorescence Compounds Having Various Donor–Acceptor Spacers Prepared by the Combination of Carbon–Carbon Bond and Carbon–Nitrogen Bond Cross-Coupling Reactions

A family of novel linear 1,10-phenanthroline-based (A–D–A–D–A) and oligothiophene-based (A–D–D–D–(D)–A) heterocyclic aromatic fluorescence compounds having N-containing imidazole and pyridine tails with effective π-conjugated systems, prepared by the combination of carbon–carbon (C–C) bond and carbon–nitrogen (C–N) bond cross-coupling reactions, is described. They have molecular lengths of more than 2.30 nm in the cases of 4, 6, 9, and 26, various D–A spacers, and certain N-coordination sites (phen, imidazole, and pyridine). X-ray single-crystal structures of 13 compounds reveal a variety of trans and cis configurations with different dihedral angles between adjacent aromatic heterocycles. Synthetic, computational, and spectral studies have been made to reveal the differences between cross-coupling approaches on the C–C bond and C–N bond formation as well as band gaps and energy levels and optical and electrochemical properties for related compounds. The influences of introducing a β-methyl group to the thiophene ring on reaction activity, solubility, and conformation of related compounds have also been discussed.