Water-Soluble Nile Blue Derivatives: Syntheses and Photophysical Properties

Four water-soluble 2-hydroxy-Nile Blue derivatives, 1a, 1b, 2 a, and 2b, were prepared by condensation reactions performed under relatively mild conditions (90 degrees C, N,N-diniethylformamide with no added acid). These fluorescent probes had more favorable fluorescence characteristics than two known water-soluble Nile Blue derivatives. Specifically, they were superior to the known dyes with respect to their quantum yields in aqueous media and the sharpness of their fluorescence emissions. Concentration-dependant UV absorption and fluorescence emission studies indicated that the dyes did not aggregate in aqueous solution at concentrations of less than 1-4 mu m. The now water-soluble materials 1a, 1b, 2a, and 2b emit in a desirable region of the fluorescence spectrum (lambda=670-675nm). Overall they are potentially interesting for labeling biomolecules in aqueous environments.