Synthesis, Electrochemistry, Crystal Structures, and Optical Properties of Quinoline Derivatives with a 2,2′-Bithiophene Motif

New quinolines bearing a 2,2′-bithiophene motif have been prepared through Ru- and In-catalyzed reactions as well as by Suzuki cross-coupling reactions. The novel quinolines have been characterized by using EI-HRMS and NMR spectroscopy. Additionally, the molecular structures of the novel quinolines were confirmed by X-ray crystallography. The photophysical and electrochemical properties of all quinoline derivatives were investigated by using absorption and luminescence spectroscopy and cyclic voltammetry. The main intense absorption bands associated with the quinoline derivatives were located between 350 and 450 nm. Intense blue-green and orange-red fluorescence, moderate Stokes shifts, and microsecond lifetimes were observed. Quinolines containing one bithiophene moiety underwent oxidation leading to dimerization, whereas bis(bithiophenyl)-substituted quinoline underwent polymerization. All the studied quinolines showed multistep reversible reduction, with 6-nitro-4-phenylquinoline being the easiest to reduce. The study of novel quinoline derivatives indicates a strong correlation between their electrochemical and spectroscopic properties and the character of the substituent (electron-donating or electron-withdrawing) in the quinoline ring.