Excited State Dynamics of Alizarin Red S Nanoparticles in Solution

Alizarin red S is a sulfonated, water-soluble derivative of alizarin. This work presents femtosecond studies of alizarin red S (ARS) nanoparticles in comparison to ARS in aqueous solution and to alizarin in DMSO. The femtosecond studies cover a probing spectral range of 350-750 nm using different excitation wavelengths, taking into account the variation of the absorption spectra with the pH values of the solvent. Stationary absorption spectra show slight differences between solution and nanoparticles. Excitation at 530 nm results in low and noisy responses, therefore, we additionally recorded transient spectra of the nanoparticles at & lambda;(ex) = 267 nm. While the results in DMSO are comparable to previous studies in non-aqueous solvents, we report a relatively fast relaxation of 14 ps in [La(OH)(2)][ARS] nanoparticles in aqueous solution after excitation at 530 nm, which is similar to Na(ARS) solution (19 ps). The dynamics changed with lower pH, but still without significant differences between nanoparticles and solution. We propose [La(OH)(2)][ARS] nanoparticles as a suitable alternative to dissolved molecules with similar spectroscopic properties, for example, with regard to biomarker applications.

Automated summary

This study compares the characteristics of water-soluble dye alizarin red S (ARS) nanoparticles, ARS in aqueous solution, and alizarin in DMSO using femtosecond technology. The results show slight differences in the stationary absorption spectra between nanoparticles and solution. Excitation at 530 nm leads to weak and noisy responses, and transient spectra of the nanoparticles at 267 nm were recorded. The [La(OH)(2)][ARS] nanoparticles in aqueous solution exhibit a fast relaxation process of 14 ps after excitation at 530 nm, similar to Na(ARS) solution (19 ps).