Conformation of Novel Azo-Dyes Bearing End-Capped Oligo(ethylene glycol) Studied by UV–vis and NMR Spectroscopy
Résumé
Two novel azo-dyes bearing an end-capped oligo(ethylene glycol) chain were synthesized and then studied by UV–visible and NMR spectroscopy. For both azobenzenes, the end-capped oligo(ethylene glycol) segment is on the para position of the first phenyl ring. On the second phenyl ring, a methoxy group is added on the para position for one azo-dye and no substitution group on the other, which made them electronically a push–push and a push system, respectively. The presence of the methoxy group changes significantly the absorption and the photoisomerization behaviors and results in a much less intense absorbance for the trans isomer and a shift from 350 to 360 nm. In the kinetic studies the azobenzene bearing a methoxy group shows a zero-order and a first-order kinetics as a function of the time scale of the study as well as an aggregation phenomenon. This azo-dye in different solvents has been studied by 1H NMR and pulsed gradient NMR experiments to understand the effects of the photoisomerization and the aggregation on the self-diffusion of these molecules in solutions.