Photophysical Properties of Nanodiamonds Covalently Bonded to N-Substituted 1,8-Naphthalimide

With the aim of obtaining new fluorescent biomarkers, we have synthesized nanodiamond–dye dyads which form a stable aqueous suspension. In the dyads, by means of nucleophilic substitution of the nitro group, the N-substituted 4-nitro-1,8-naphthalimide was added to the ultradisperse nanodiamonds via a long alkyl chain. We studied the absorption and fluorescence spectra and also the fluorescence decay kinetics for the dyads. We propose that the non-exponential fluorescence decay for the dyads in aqueous suspension is due to two ways to position the plane of the N-substituted 1,8-naphthalimide relative to the plane of the nanodiamond.