Photoluminescent properties of Rhodamine 6G in the nanoaggregates of poly(ethylene oxide)-b-polymethacrylate in aqueous solutions

Absorption and fluorescence spectra of Rhodamine 6G (R6G), as well as degree of polarization (P) and lifetime of fluorescence, have been measured in order to investigate the usefulness of R6G as a photoluminescent probe for the micelle-like nanoaggregates formed from poly(ethylene oxide)-b-polymethacrylate (PEO-b-PMA) and counter ions. The counter ions used are cetyltrimethylammonium chloride (CTAC), dibucaine (DC), tetracaine (TC), poly-l-lysine (PLS), and alkaline earth metal ions (Ba2+ or Ca2+). The change in the spectrum or P value in CTAC/PEO-b-PMA and DC/PEO-b-PMA systems indicates that R6G is useful for detecting and characterizing the aggregates. However, the fluorescence parameters do not significantly change when TC, PLS, Ba2+, and Ca2+ are used as a counter ion. The difference is discussed based on the hydrophobicity of the counter ions and the structures of the aggregates.