Synthesis and Photophysical Studies on Naphthalimide Derived Fluorophores as Markers in Drug Delivery

Derivatives of 4-amino-1,8-naphthalimide containing a free alkyl chain bearing carboxyl group as linker and different substituents at 4-amino function have been synthesized, characterized and studied for their photophysical properties. Steady state fluorescence studies showed quantum yield varied from 0.45 to 0.65 with Stokes shift in the range of 5824–8558 cm−1. Spectroscopic and physicochemical parameters, like electronic absorption, emission, and extinction coefficient were investigated in order to explore the analytical potential of compounds. Solvatochromic studies demonstrated that all compounds were sensitive towards the polarity of different solvents showing the highest degree of fluorescence in acetonitrile. In addition, the compounds in the presence of ions, viz. Na+, K+ and Mg2+ at concentration of 0.1–2 equivalents, showed a decreasing trend in fluorescence with increasing ionic concentration. TCSPC set – up was used to measure the fluorescence lifetime of compounds, which was found to be bi-exponential with longer and shorter component at their respective amplitudes. The average lifetime of compounds was observed to be 5.76–9.96 ns indicating the possibility of their greater utilization in research and diagnosis.