Synthesis And Properties Of Rhodamine End Groups Of Poly N-isopropyl Acrylamide

Rhodamine dyes are widely used as fluorescent probe because of their unique structural and fluorescent property. Typically, the rhodamine-based probes prefer their spirolactam ring-closed state, which shows little fluorescence, whereas ring-opening of the corresponding spirolactam induced by metal ions gives rise to the enhanced fluorescence. By virtue of these fascinating properties, excellent examples of rhodamine-based turn-on fluorescent probes have been reported.In this study, Rhodamine 6G, used as raw material, reacted with hydrazine hydrate to get rhodamine derivative(R6G-NH2) terminus with a reactive amino group. Then HN-R6G-Br was prepared using α-bromoisobutyryl bromide and R6G-NH2. A series of well-defined rhodamine end groups poly N-isopropylacrylamide(HN-R6G-PNIPAM) were synthesized via transfer radical polymerization(ATRP), where HN-R6G-Br used as the initiator, CuBr and three-(N,N-dimethylaminoethyl) amine(Me6TREN) used as the catalytic system, N-isopropylacrylamide(NIPAM) uesd as the monmer. The products were characterized by fourier transform infrared spectrometry(FT-IR) and nuclear magnetic resonance spectroscopy(NMR).The molecular weight of HN-R6G-PNIPAM was firstly studies by GPC tests. The result showed that the molecular weight of the polymer increases with the increasing of polymerization time and the polymer has low polydispersity indice(PDI=1.13~1.28). Turbidity method was also used to test the temperature-sensitive of the polymer probe. The result showed that with the increase of polymer molecular weight(from 2300 to 12100), its lower critical solution temperature(LCST) decreased, and finally approaching to the LCST(32 °C) values of PANIPAM. The sensoring properties of HN-R6G-PNIPAM for Hg2+ ions were studied by fluorescence. The result showed that HN-R6G-PNIPAM can be used as a fluorescent probe to detect Hg2+ with good selectivity. With the increase of the concentration of Hg2+, it showed fluorescence enhancement trend. Thus, the polymer has a very broad application prospects in the future as it has multiple features with water-soluble, temperature sensitivity, selectivity for Hg2+.