Synthesis and properties of polyfluorohydroxyacridines and their Zn2+ complexes: New materials for solid state emitting systems

1,2,3,4-tetrafluoroacridines are easily accessible by refluxing electron-rich aromatic amines with pentafluorobenzaldehyde. This procedure, however, falls when 4-hydroxyaniline is employed for the preparation of the corresponding tetrafluorohydroxyacridine. The synthesis of this substrate, here described, has been accomplished by an indirect methodology: the synthesis of the corresponding tetrafluorornethoxyacridine was followed by the ether function cleavage by refluxing them in 47% aqueous HBr. In the case of 1,2,3,4-tetrafluoro-9-methoxyacridine a peculiar reactivity has been observed, indeed the substitution of a fluorine by a bromine atom occurs contemporaneously with the ether hydrolysis. The position of bromine on acridine moiety has been ascertained by X-ray analysis on a single crystal of this compound. The fluorine substitution did not occur when the hydrolysis was carried out employing the ionic liquid triethylammonium eptachloro alluminate. The synthesized polifluorohydroxyacridines have been fully optically and spectroscopically characterized. 1,2,3,4-Tetrafluoro-9-hydroxyacridine and 2-bromo-1,3,4-trifluoro-9-hydroxyacridine were employed to prepare complexes with Zn2+. These complexes were optically characterized by optical absorption and photoluminescence both in solution and in the solid state, and a preliminary discussion about the photophysics of these complexes is presented.