9-thioacridinones and 9-aminoacridines including six crown etherderivatives. The effect of solvents and of the addition of cations (Na+, K+, Ca2+ and Mg2+) on these properties has been studied. The absorption of the crown etherderivative of 9-thioacridinone is sensitive to solvents while the fluorescence of crown ethersderivedfrom 9-aminoacridines shows some specificity towards cations. Empirical modeling