FRET function of polymeric ionic liquid film containing rhodamine moieties for exhibiting emissions by excitation at wide wavelength areas

This paper reports synthesis of an imidazolium-type fluorescent polymeric ionic liquid film containing rhodamine moieties, which shows fluorescence resonance-energy-transfer (FRET) property, resulting in emissions by excitation at wide wavelength areas. First, radical copolymerization of two polymerizable ionic liquid, which had one and two polymerizable groups, respectively, was carried out with AIBN as an initiator to confirm whether a transparent polymeric ionic liquid film could be produced. Then, radical terpolymerization of the two ionic liquids with a rhodamine derivative having a polymerizable group was performed under the similar conditions as that for the above copolymerization to give the fluorescent polymeric ionic liquid film containing rhodamine moieties. The fluorescence spectra of the resulting film exhibited emissions due to the rhodamine group by excitation at wide wavelength areas. This result indicated occurrence of FRET from the polymeric ionic liquid units to the rhodamine moieties in the film because the excitation-wavelength-dependent emissions due to the polymeric ionic liquid were partially overlapped with an absorption peak due to the rhodamine group.