Polymerization and conformational transition of poly(methacrylic acid) probed by electronic spectroscopy of aminoacridines

9-Aminoacridinium vinyl monomers with intramolecular charge transfer (ICT) state were studied as molecular probes for copolymerization with methacrylic acid. The fading of the dye color after its addition to the poly(methacrylic acid) (PMA) chain leads to sweeping spectral changes from a broad absorption band in the red region before the polymerization to structured absorption and emission bands in the blue region after labeling. Also, the dyes bound lost their multiexponential decay behavior due to the ICT process and have only a single lifetime of the locally excited state of the aminoacridinium fluorophore. The conformational transition of PMA is sharply determined at pH = 5.2 by time-resolved fluorescence anisotropy. This probe technique also indicates strong polymer segments interactions prior to the critical transition of the chain opening with increases of the pH of the aqueous PMA solution.