Spectrophotometric Studies of a Fluorescent Naphthalenediimide PET and ICT pH Indicator and DNA Intercalator.

Three naphthalenedimides (NDIs) were studied by UV-visible absorbance, fluorescence and circular dichroism spectroscopy in aqueous methanolic solution as DNA intercalators. Distinct solution colours are observed for the compounds under room lighting and upon irradiation with 365 nm UV light. The tetra-substituted dimethylaminoethylene NDI is designed as a fluorescent pH indicator with a 'fluorophore-spacer-receptor' construct based on a photoinduced electron transfer (PET) mechanism. This NDI derivative exhibits a significant change in the ellipticity with calf-thymus DNA. Fluorescence DNA titrations further revealed strong binding towards DNA, resulting in pronounced emission quenching. Incubation of MCF-7 cells reveals localisation of the fluorescent probe in the nucleus, specifically in the nucleoli.