Luminescence of Eu(DBM)3Phen-doped in azobenzene-containing copolymers--effects of absorption overlapping of two components.

Poly(N-isopropylacrylamide)-b-poly[6-[4-(4-methylphenyl-azo)phenoxy]hexylmethacrylate] (PNIPAM(32)-b-PAzoMM(8)) and poly(N-isopropylacrylamide)-b-poly[6-[methyl(4-nitrophenyldiazenyl)phenyl]aminohexylmethacrylate] (PNIPAM(32)-b-PAzoNO(10)) were prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization. The optical properties of Eu(DBM)(3)Phen (Eu, Europium; DBM, dibenzoylmethide; Phen, 1,10-phenanthroline)-doped azobenzene-containing copolymer vesicle solutions were studied by UV-vis and fluorescence spectroscopy. When the electronic transition bands of azobenzene and Eu(DBM)(3)Phen overlapped at about 350 nm in PNIPAM(32)-b-PAzoMM(8), the fluorescent emission intensity at 612 nm of Eu(DBM)(3)Phen could be modulated by irradiation with UV and visible light. However, when the absorption of the azobenzene-moiety red-shifted to 477 nm in PNIPAM(32)-b-PAzoNO(10), the luminescence intensity of Eu(DBM)(3)Phen was not affected any longer. The difference between these two systems was possibly caused by the energy allocation in the luminescence process, which was discussed in detail.