Synthesis, characterization, and optical properties of a novel azo-dye bearing an oligo(ethylene glycol) methyl ether side chain in solution and in the solid state

A novel azobenzene compound bearing a short poly(ethylene glycol) methyl ether side chain, N-methyl-N-{4-[(E)-(4-nitrophenyl)diazenyl]phenyl}-N-(3,6,9,12,15,18,21,24-octaoxapentacos-1-yl)amine (RED-PEGM-8) was synthesized and characterized. RED-PEGM-8 exhibits a thermal behavior similar to that of Disperse Red-1; however, its thermal stability, as well as its Tg and Tm values, are lower because of the presence of the PEGM segment. The optical properties of this compound in solution and in the solid state were studied by UV–vis spectroscopy. The appearance of a blue-shifted band in aqueous solutions at high concentrations of the chromophore reveals the existence of H-type aggregates, resulting from π–π intermolecular interactions between the azobenzene units. Strong intermolecular interactions were also confirmed by 1H NMR measurements. Optical properties of RED-PEGM-8 in the solid state (thin film) also suggest the presence of H aggregates. However, a tail is also detected in the red region of the absorption spectrum, which could be because of the formation of J-type aggregates in the thin film.Key words: aggregation, azo-dye, poly(ethylene glycol) methyl ether.