Nile red is a fluorescent solvatochromatic dye. The absorbance and emission maxima increase with polarity of the solvent whilst the fluorescence intensity decreases with solvent polarity. Nile red has been incorporated into a series of hyperbranched n-isopropyl acrylamide polymers by polymerizing nile red acrylate with n-isopropyl acrylamide in the presence of a branching RAFT agent. Polyn-isopropyl acrylamide in aqueous solution undergoes a coil to globule transition as the temperature passes the lower critcal solution temperature (LCST).<br/>When incorporated in hyperbranched polyn-isopropyl acrylamide nile red maintains its solvatochromism. In addition to being influenced by solvent polarity it responds to changes in its 'micro environment' created by altering the amount of branching in the polymer and also responds to a change in environment when the coil to globule transition occurs at the LCST.<br/>Visible spectrometry shows that λmax values for polymers is influenced by branching i.e. λmax is lower for branched polymers than linear polymers. When aqueous solutions of the polymer are heated to the LCST there is a decrease in the absorbance and emission maxima and an increase in the fluoresence intensity. The nile red is sensing a change from the polar aqueous environment of the expanded polymer coil to a less polar predominantly polymer environment when the chains collapse and expel water forming a globule.

Incorporation of Nile red in hyperbranched poly n-isopropylacrylamide and its response to environmental change

253rd National Meeting (2017)

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