Morphology and photophysical properties of a thermally responsive fluorescent material based on a rod-coil tri-block copolymer

A thermally responsive rod-coil poly[poly (N-isopropylacrylamide)-b- polyfluorene-b-poly(N-isopropylacrylamide)] triblock copolymer has been successfully synthesized by atom transfer radical polymerization from an end-functionalized macroinitiator. The thermochromic behavior and relevant morphology of this polymer were investigated by UV-vis spectra, DLS, and AFM, respectively, at various temperatures. A thermally responsive fluorescent material was achieved facilely by combining the optically active polyfluorene with temperature-responsive poly(N-isopropylacrylamide). All the measurements demonstrated that in the region of 25-45°C, the polymer underwent a phase transition and the corresponding change in optical properties in its water solution. However, the polymer did not show completely reversible behavior upon heating and cooling. On the basis of the comparison with two other thermally responsive conjugated polymers in literatures, a tentative mechanism has been proposed that π-π interaction induced rigid segments to remain chain conformation and packing styles as in collapsed state.