Luminescence and structure of Eu(DBM)₃Phen-doped vesicles composed of amphiphilic PNIPAM-b-PAzoM

Eu(DBM)₃Phen-(DBM = dibenzoylmethide; Phen = 1,10-phenanthroline) doped vesicles were obtained through the self-assembly of poly (N-isopropylacrylamide)-b-poly{6-[4-(4-methylphenyl-azo) phenoxy] hexylacrylate} (PNIPAM-b-PAzoM) in the presence of Eu(DBM)₃Phen in the H₂O/THF solution (50/50 vol.%). When the water content of the vesicle solution increased from 50 vol.% to 98 vol.%, the characteristic luminescence of Eu(DBM)₃Phen at 612 nm appeared. Moreover, with the increased water content, luminescence intensity gradually increased by about 200 times from 50 vol.% to 98 vol.% of the water content. A further detailed study on this phenomenon has shown that azobenzene units and Eu(DBM)₃Phen were located in the shell of the vesicle, such that when more water was added into the solution, azobenzene units aggregated to a larger extent as demonstrated by their subsequent absorption-shift. From our results, we find that it is the more hydrophobic environment within the shell that has made the fluorescence of Eu(DBM)₃Phen stronger. Such an environment hinders the interactions between water molecules and the complex. In this study, a model is presented for the azobenzene-containing vesicle in order to explain this phenomenon. Crown