Amphiphilic Near-Infrared Fluorescent Molecular Probes: Optical Properties in Solution and in Surfactant Micelle Microenvironment

In this work, the optical properties of two novel near-infrared fluorescent tricarbocyanines with amphiphilic nature, CyN and CyS, were studied in solution and in micelles of representative surfactants (anionic, cationic and non-ionic) by means of spectroscopic techniques. Interestingly, the spectral properties of the new fluorophores depend on the nature of the heteroatom at the meso position. Dependence on the solvent polarity and the viscosity were also observed in both cases. Furthermore, changes on photophysical properties occurred upon encapsulation of the dyes. The incorporation of the dye from the aqueous solution to the surfactant supramolecular assembly produced a drastic change in the fluorescence emission from quenched state to fluorescence enhancement, rendering an OFF-ON response to the exchange of environment. In addition, a significant protective effect against photobleaching was determined when the dyes were included in Pluronic (R) micelles (F127) resulting in a promising system to be used as a fluorescent nanosized container. The novel amphiphilic NIR fluorophores also interact as a Forster resonance energy transfer (FRET) pair and the process was studied within micelles loaded with both dyes.