Comparing the spectral properties of pyrene as free molecule, label and derivative in some colloidal systems

• Micelles are appropriate aggregates for hydrophobic substances solubilization.
• Pyrene senses each change of its microenvironment.
• As such pyrene is located in the core of the free or polymer-bound micelle.
• The derivative and labeled pyrene are solubilized in the micellar palisade layer.
• The studied fluorophores sense the hydrophobically microdomains formation.

This paper investigates the behavior of pyrene as free molecule (probe), label and derivative in some colloidal systems. Aqueous octaethylene glycol mono n-dodecyl ether (C12E8) with or without poly(acrylic acid) (PAA), and a hydrophobically modified polyacrylate are considered. The effect of C12E8 on PAA labeled with pyrene is also studied. As a probe, pyrene has a typical behavior in the absence or presence of PAA. The labeled PAA has the peak corresponding to the sandwich excimer even in the absence of surfactant. The pyrene derivative is 4-(N′,N′-diphenyl-hydrazine)-3,5-dinitrobenzoic acid 2-oxo-2-pyren-2-yl-ethyl ester. Its fluorescence emission is low and bathochromically shifted by 9 nm with respect to pyrene. The low fluorescence emission of derivative is due to its self-quenching. The data reveal that pyrene probe is located in the free or polymer-bound micelles. The labels on PAA create hydrophobic domains and shrink the polymer coil. By surfactant addition, labeled pyrene is solubilized in micelles palisade layer, closer to the ethylene oxide (EO) chains. The derivative is also located into the micellar palisade layer, in the proximity of the EO groups. The fluorophore behavior is discussed in relation to the critical points of surfactant and polymer–surfactant systems.