Synthesis and fluorescence study of 3-aminoalkylamidonapthalimides

A new series of fluorescent 3-aminoalkylamidonapthalimides were synthesized starting form 1,8-naphthalic anhydride. The structure of these compounds was characterized by 1H NMR, 13C NMR, IR and Mass spectral analysis. The solvent effect on 1H and 13C NMR of these compounds was studied in CDCl3, CDCl3:DMSO-d6 (7:3, v/v) and DMSO-d6. NMR chemical shift of the ortho and para protons and meta carbons of naphthalene ring showed maximum variation on moving from CDCl3 to DMSO-d6. In CDCl3 solvent naphthalene ring may exist in slightly puckered form while in DMSO-d6 it attains maximum planar configuration. Fluorescent properties of the title compounds and their precursors were investigated in different solvents like chloroform, ethanol, acetonitrile, acetone, DMSO and water. 3-Aminoalkylamidonapthalimides exhibited improved fluorescence than their precursors. Cyclic amino derivatives yielded higher fluorescence quantum efficiency in protic solvents, ethanol and water. Acylic amino derivatives yielded high fluorescence quantum efficiency in chloroform solvent. The maximum fluorescence quantum yield up to 0.14 was found for butyl amine derivative in chloroform solvent. In general proton accepting nucleophilic solvents like acetone and DMSO quenched the fluorescence.

Graphical abstract3-Aminoalkylamido napthalimides derivatives were prepared and their fluorescent properties were studied in different solvents. Dipolar aprotic solvents quenched the fluorescence while in chloroform and proton donating solvents the fluorescence is enhanced. In proton NMR spectrum the ortho and para protons of napthalene ring appeared as two separate signals in CDCl3 while in DMSO-d6 these protons resonated at the same frequency.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Solvent and structure dependent fluorescence. ► Solvent dependent 1H and 13C NMR. ► Synthesis of alkylamino substituted naphthalimdes by simple nucleophilic substitution.