4.2. pH- and multi-responsive conjugated rod–coil block copolymers
Our group reported a novel multifunctional copolymer consisting of a PNIPAAm segment and a fluorescent difluorene-containing acrylic polymer segment with pH responsiveness and/or DNA-sensing ability [29]. The protonation of the amino moiety at a low pH improved the solubility and prevented aggregation and resultant fluorescence quenching (Fig. 42). Although the aggregation of the fluorene units was significant at room temperature under basic pH conditions, with resultant fluorescene quenching and alteration of the emission spectrum, the quenching was suppressed, and the spectrum returned to its form in acidic medium as the temperature was increased above the LCST. This is attributed to some isolation of the rodlike entities in the globular phase separated globes, suppressing aggregation. Moreover, after the amino groups were quaternized, the copolymer could be used as a biosensor because the fluorescence intensity was quenched with the addition of DNA, an example of a multifunctional material with pH- and temperature-sensing characteristics and biological molecules realized by the incorporation of a functional fluorene-containing moiety with PNIPAAm