Synthesis, Photophysical Characterization, and Sensor Activity of New 1,8-Naphthalimide Derivatives.

Three new 1,8-naphthalimide derivatives - with different substituents at the C-4 position have been synthesized and characterized. Their photophysical properties have been investigated in organic solvents of different polarity, and their fluorescence intensity was found to depend strongly on both the polarity of the solvents and the type of substituent at C-4. For compounds and having a tertiary amino group linked via an ethylene bridge to the chromophore system, high quantum yield was observed only in non-polar media, whereas for compound , the quantum efficiency did not depend on the medium polarity. The effect of different metal ions (Ag, Ba, Cu, Co, Mg, Pb, Sr, Fe, and Sn) on the fluorescence emission of compounds and was investigated. A significant enhancement has been observed in the presence of Ag, Pb, Sn, Co, Fe, as this effect is expressed more preferably in the case of . Both compounds have shown significant pH dependence, as the fluorescence intensity was low in alkaline medium and has been enhanced more than 20-fold in acidic medium. The metal ions and pH do not affect the fluorescence intensity of . Density-functional theory (DFT) and Time-dependent density-functional theory (TDDFT) quantum chemical calculations are employed in deciphering the intimate mechanism of sensor mechanism. The functional properties of and were compared with polyamidoamine (PAMAM) dendrimers of different generations modified with 1,8-naphthalimide.