Spectroscopy of auramine fluorescent probes free and bound to poly(methacrylic acid)

Auramines containing a vinyl group with strong electron-withdrawing substituent exhibit a pi-conjugated extended effect that gives a red shift in their absorption and emission bands. The new fluorochromic dyes were bound to poly(methacrylic acid) (PMA), and their photophysical dynamics in methanol and in aqueous solution were studied. These derivatives were also used as optical probes for copolymerization process. The process was monitored by the changes in electronic absorption with a concomitant fading of the free vinyl auramine absorption band in the red and an appearance of a UV band ascribed to dye bound to the polymer chain. The conformational transition of PMA with solvent and pH was clearly observed by the drastic changes in the photophysical properties of these auramine derivatives attached to the polymer chain. Time-resolved experiments revealed an unusual long-lived decay component of about 2.2-2.6 ns in aqueous solution at low pH together with two picosecond components (50 and 570 ps). Such long decay was only reported in the literature for auramine adsorbed in solid matrices. It was ascribed to the fraction of bound auramine in a region of compact coil of PMA.