Positional Isomeric Thiophene-Based π-Conjugated Chromophores: Synthesis, Structure, and Optical Properties

A series of positional isomeric chromophores o-TC, m-TC, and p-TC, in which electron-rich thiophene moieties were connected by pi-conjugated bridges, were divergently synthesized and characterized. Single-crystal X-ray diffraction analysis revealed an intriguing zipper-like packing mode which was adopted by m-TC in the solid state. Subsequently, UV-vis absorption spectra and fluorescence spectra in a series of solvents were investigated. The nearly coplanar para isomer p-TC was found to have the most intense UV-vis absorption, fluorescence emission, and the highest photoluminescence quantum yield. The molecule structure, electronic nature, and origination of the absorption of p-TC were revealed through density functional theory calculations. Interestingly, all three positional isomers exhibited strong and stable electrochemiluminescence emission, which enriched the existing knowledge on the optical properties of thiophene-based oligomers.