The synthesis and fluorescence properties of some substiuted naphthalimides

Abstract

A number of known and novel naphthalimide derivatives have been synthesised. For many of the known compounds, improvements in their syntheses have been achieved in terms of higher yield and/or milder reaction conditions. Some of the novel compounds have been prepared with the aim of improving the water-solubility of the system by the introduction of
substituents containing polar terminal groups and by sulfonation on the naphthalene ring. The sulfonated compounds exhibit quite good watersolubility and the others also show some improvement. Chloroacetyl and maleimido functions have been introduced into naphthalimides as reactive groups for attachment to biological molecules. Some brominated naphthalimides have been prepared for a study of their photochemical properties.
The absorption and fluorescence properties of the synthesised naphthalimides have been studied. The maximum absorption wavelengths and extinction coefficients of their ultraviolet/visible spectra and their fluorescence spectra together with quantum yields and lifetimes have been measured for the naphthalimide compounds. The effects of the substituents on the photophysical properties were studied. The fluorescence properties of 4-(n-butylamino)-9-(n-butyl)-1,8-naphthalimide were investigated in a range of organic solvents including binary solvent mixtures and aqueous solution containing sodium dodecyl sulfate. The environment-dependence of the fluorescence properties indicates a potential for the naphthalimides to be used as fluorescent probes and labels. The heavy atom quenching effect in the fluorescence quantum yields and lifetimes of the 3-bromonaphthalimides have been observed in the selected organic solvents. The fluorescence properties of some naphthalimides have been studied in ethanol and water.
Specific solvent effects on the naphthalimide emission properties have been observed. The photophysical behaviour of a series of 4-amino-9-aminoalkyl-1,8-naphthalimides in water were studied as a function of pH. Changes in the absorption and fluorescence properties of the compounds due to the protonation of the 4-amino group were observed and used for calculation of the pKa5 and fluorescence quenching constants of the naphthalimides.