Three aminonaphthalimide derivatives were synthesized bearing different anchoring groups in their 4-position in order to adjust the supramolecular interactions with carboxylato-pillar[5]arene (WP5), an anionic, water-soluble host. The modification of the anchor groups resulted in varying association constants embracing three orders of magnitude (K_a from ∼10³ to ∼10⁶) in buffered water. Since the fluorophore responded significantly to the electronic environment, large fluorescence quenching was observed with the anionic WP5 host. The naphthalimide indicator–WP5 supramolecular assemblies were used to detect arginine and lysine with complete selectivity over other non-basic α-amino acids by turn-on fluorescence. The same assemblies proved to be highly sensitive fluorescence displacement assays for the detection of cadaverine.

The excited state processes in N-propyl-4-piperidinyl-1,8-naphthalimide have been studied by measuring its fluorescence spectra and decay curves in solvents of different polarity and viscosity and also in a frozen solvent glass. The results unanimously proved the formation of a dark twisted intramolecular charge transfer (TICT) state from the emissive charge transfer (CT) species, the direct product of excitation. The rate coefficients of the TICT process and the deactivations of the CT and TICT species were determined, using a reversible two-state kinetic model. The temperature dependence of the kinetic data was consistent with a kinetic barrier consisting of three terms, the inherent barrier of the reaction, and the contributions of the solute–solvent interactions related to the solvent viscosity and polarity. The potential energy surfaces were calculated in the S₀ and the S₁ states along the coordinate of turning motion which was conclusive concerning the direction of the twisting and indicated a possible conformational change of the piperidinyl unit. The theoretical calculations confirmed that the TICT species is dark and has a stronger charge transfer character compared to the CT state.

The host–guest interactions of a water soluble carboxylato-pillar[5]arene (WPA5) and three stilbazolium dyes (containing 9-anthryl, 1-pyrenyl and 4-dimethylaminophenyl groups) were studied by UV-Vis and fluorescence spectroscopy giving a detailed description of the spectral changes. A different spectroscopic response was observed in each case, with the most significant result of 28-fold fluorescence enhancement and intense color change in the case of 4-dimethylaminostyryl-N-methylpyridinium iodide (DAST, G3). In addition, a FID (fluorescence indicator displacement) system comprised of WPA5 and G3 was shown to detect paraquat by turn-off fluorescence in aqueous solution.