Synthesis, optical properties and self-assembly of phenylene ethynylene dimers with alkyl side chains

Five phenylene ethynylene dimers (PEDs) with alkyl side chains were synthesized and characterized by UV–vis absorption, fluorescence emission spectroscopy and cyclic voltammograms. The UV absorptions maximum peaks range from 311 to 324 nm in cyclohexane solution, which are red-shifted with the increase of the carbon numbers of alkyl groups. The fluorescence emissions are originated from the phenylene ethynylene backbone, which maximum fluorescence peaks all appear at about 417 nm. The quantum yields of fluorescence vary from 0.36 to 0.57 in cyclohexane. This series of compounds could be dissolved in common organic solvents and form self-assembled monolayers (SAMs) on gold surfaces. Electrochemical investigation shows that the density of the SAMs depends on the size of the alkyl side chain.