<p>A new symmetrical and a new unsymmetrical Schiff bases are synthesized by condensing 1-(2,4-dihydroxyphenyl)ethanone with, Naphthalen-1-amine and Naphthalen-1,8-diamine under solvent free condition and characterized by IR, UV–visible, ¹H NMR, ¹³C NMR and mass spectral studies. Cation recognizing potentiality of both the Schiff bases is explored-of the Schiff base 4-(1-(naphthalen-1-ylimino)ethyl)benzene-1,3-diol (NEBD) in aqueous methanolic medium and of Schiff base 4,4′-((naphthalene-1,8-diylbis(azanylylidene))bis(ethan-1-yl-1-ylidene))bis(benzene-1,3-diol) (NDBD) is scrutinized in aqueous ACN medium through dual modes namely absorption and emission methods. Both the Schiff base sensors are found to detect Cu(II) ion selectively. The detection occurs in an off–on mode (increase of emission intensity of the Schiff base in the presence of Cu(II) ion) and on–off mode (decrease of emission intensity of the Schiff base in the presence of Cu(II) ion) for the Schiff bases NEBD and NDBD respectively. For the Schiff base NEBD LOD for Cu(II) ion is 1.528 × 10^–6&#xa0;M and for NDBD it is 2.871 × 10^–7&#xa0;M. The sensing property is applied in bioimaging technique for the detection of human cancer cells HeLa. Both the Schiff bases are screened for their antimicrobial activities. Schiff base NEBD is found to be more potential than the standard drug amphotericin B towards <i>Aspergillus niger.</i> Regarding Schiff base NDBD, it is as potential as the standard drug towards all the organisms studied.</p> Graphical Abstract <p>Two new Schiff bases are constructed. Their structures have been unfurled through assorted spectral studies. Their cation detection competence proved their selectivity for Cu(II) ion which is applied in bioimaging technique for HeLa cell lines. Both the Schiff bases have LOD value of the order of micro molar quantity.</p> <p></p>