Comparative analysis of the PET and ICT sensor properties of 1,8-naphthalimides containing aza-15-crown-5 ether moiety

•1,8-Naphthalimides containing aza-15-crown-5 group at C-4 and N-imide are prepared.•The sensors have been shown to bind Ca2+ ions in MeCN with different affinities.•Ion induced optical changes are strongly dependent on the position of receptor unit.•Results have been rationalized in terms of PET and ICT mechanisms.

Novel 4-amino- and 4-(acetyl)amino-N-aryl-1,8-naphthalimides containing aza-15-crown-5 ether receptor unit in the N-aryl fragment and at C-4 of the naphthalimide residue were designed and prepared. Significant internal charge transfer from electron donating amino or amido group at C-4 of the naphthalene ring to the acceptor carboxyimide moiety as well as photoinduced electron transfer between N-aryl receptor and the naphthalimide fragment was revealed by the UV/Vis absorption spectroscopy and considerable fluorescence quenching. The addition of calcium perchlorate to an acetonitrile solution of naphthalimides with the receptor at imide nitrogen hindered the photoinduced electron transfer process and accordingly restored the quenched fluorescence of the free ligands. In the case of the compound in which the aza-15-crown-5 receptor is located at C-4, the coordination with Ca2+ reduced the internal charge transfer interaction in the chromophore and caused a significant blue-shift of the absorption and emission peak. The observed spectral effects were analyzed using PM6 semiempirical calculations. Formation of complexes was also confirmed by 1H NMR spectroscopy.

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