Nanoscaled rhodamine dyes with 4.5-fold longer fluorescence lifetimes and 150 nm red shifted fluorescence spectra: Preparation, size tuning and optical properties

• Nano wired rhodamine (NWR) dyes were prepared and characterized.
• Their size is tunable by varying the concentration of rhodamine or surfactant additive.
• Their fluorescence lifetime is 4-fold longer, the emission maxima are 150 nm longer.
• The increase in size of NWR leads to large red shifts in optical spectra.
• The increase in size does not affect the fluorescence quantum yield and lifetime.

Nanoscaled rhodamine (NSR) dyes were prepared by reprecipitation method and characterized by TEM and laser diffraction analysis. The optical properties of nano wired rhodamine dyes were studied by UV–vis absorption and steady state/time resolved fluorescence. The size of NSR dyes is tunable by varying the concentration of rhodamine or surfactant additive. Compared to corresponding molecular rhodamine, the fluorescence lifetime of NSR dyes is 4.5-fold longer, while the emission maximum can be 150 nm larger. Although the increase in size of NSR dyes leads to large red shifts in optical absorption and fluorescence spectra, it does not affect the fluorescence quantum yield and lifetime. On the other hand, the presence of a surfactant (sodium dodecyl benzene sulfonate) not only causes the increase in fluorescence quantum yield, but also greatly extends the fluorescence lifetime of NSR dyes from 1.51 ns to 7.07 ns.