New brightly coloured, water soluble, core-substituted naphthalene diimides for biophysical applications

•New water soluble naphthalene diimide based dye compounds that emit in the red part of the spectrum.•Straight forward synthesis described with full molecular and photophysical characterisation.•Fluorescence lifetimes in water greater than 4 ns.•Fluorescence lifetime probes the nature of the interior of reverse micelles.•Compounds shown to be suitable for fluorescence correlation spectroscopy.

Symmetrically and dissymmetrically core-substituted amino naphthalene diimides (cNDIs) with water-soluble substituents have been synthesised. The compounds display characteristic steady-state optical properties absorbing and emitting light in the visible part of the electromagnetic spectrum. Time-resolved fluorescence studies reveal long emission lifetimes of ∼10 ns in chloroform, ∼8 ns in methanol and ∼4 ns in water. Suitability for use in biophysical applications is demonstrated by encapsulation into reverse micelles and liposomes. Fluorescence lifetime is shown to indicate cavity size in the reverse micelles and fluorescence correlation spectroscopy measurements of cNDI loaded liposomes successfully determined diffusion coefficients and hydrodynamic radii of the liposomes.

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