Highly solvatochromic fluorescent naphthalimides: design, synthesis, photophysical properties and fluorescence switch-on sensing of ct-DNA.

We report the design, synthesis and photophysical properties of highly solvatochromic donor/acceptor substituted naphthalimide based fluorophores. The synthesized naphthalimides containing propargyl ends showed highly solvatochromic intramolecular charge transfer (ICT) feature as was revealed from the UV-visible, fluorescence photophysical properties of these fluorophores and DFT/TDDFT calculation. Fluorescence life times for the imide fluorophores were also measured in different solvents. The solid state photophysical property of donor substituted naphthalimide 1 showed promising for future application in material sciences. Furthermore, both the donor/acceptor substituted naphthalimide fluorophores 1-2 were exploited in sensing calf-thymus DNA via switch-on fluorescence response. The propargyl linker containing naphthalimides can further be exploited for the synthesis of labeled biomolecular building blocks.