Complexation of fluorescent dyes rhodamine B, auramine O, and fluorescein, as well as the antitumor drug thymoquinone with disubstituted phenanthridine derivative of calix[4]arene, 5,11,17,23- tetra-tert-butyl-25,27-(bis(6-phenanthridinemethoxy)-26,28-dihydroxycalix[4]arene (L), was studeied by means of spectrophotometric titrations in the solvent system acetonitrile/dichloromethane, at room temperature. By processing the experimental data, the stability constants of the complexes of compound L with rhodamine B and auramine O were determined, while the stability constant of the complex of compound L with fluorescein could not be determined, although the formation of the complex was noted. Compound L did not bind the antitumor drug thymoquinone under the experimental conditions used in this bachelor thesis. Comparison of the values of the stability constants of the complexes of compound L with rhodamine B and auramine O, showed that compound L exibits equal affinity for the binding of both dyes and forms fairly stable complexes with them. The obtained experimental data lead to the conclusion that phenanthridine subunits on the endo rim of the calixarene derivative L provide a good binding site for the tested dyes, and therefore this derivative, modified at the exo rim with substituents that would ensure its solubility in water, could have great potential for application in theranostics.