Light and temperature responsive block copolymer assemblies with tunable fluorescence emissions

Abstract A dual-responsive amphiphilic diblock copolymer, poly(styrene- co -1-(2-methacryloxyethoxy)-2-(2-pyridyl)benzimidazole)- block -Poly( N -isopropylacrylamide- co -3-biphenyl-3-phenyl-8-methacryloxy-3 H -naphtho[2,1- b ]pyran- co -4-methamino-9-allyl-1,8-naphthalimide), also denoted as P(St- co -PBI)- b -P(NIPAM- co -NP- co -MANI), was synthesized by reversible addition fragmentation chain transfer polymerization followed by assembling into micelles with hydrophobic P(St- co -PBI) block as core and thermoresponsive P(NIPAM- co -NP- co -MANI) block as the shell in aqueous solution. Dynamic light scattering, transmission electron microscopy and optical transmittance were used to characterize the particle morphology and thermosensitivity of the micelles solution. In addition, the fluorescence emission of the micelles could be reversibly modulated “on” and “off” by the photochromic naphthopyran upon UV and thermal back reaction, which promoted naphthopyran transformation between merocyanine forms and original closed form. Moreover, the spatial distance between the two fluorescence dyes could be regulated by temperature, resulting from the collapse or extension of PNIPAM in aqueous solution. This property enabled the polymeric assemblies to serve as sensitive ratiometric fluorescent thermometers.