Acridine derivatives are widely used as antiseptics, disinfectants, antibiotics, and fluorescent dyes as well as a subunit of optical sensor molecules of various analytical applications. We reported here the synthesis of several new 9‐substituted‐4,5‐dimethoxyacridine derivatives (9‐bromo‐, 9‐(p‐methylphenyl)‐, 9‐(p‐benzyloxyphenyl)‐, 9‐azido‐, 9‐phenyltriazole‐, 9‐[(trimethylsilyl)ethynyl]‐, 9‐nitrile‐) as potential multifunctionalizable fluorescent precursors of sensor molecules, indicators or dyes including optimized procedures for preparation of 9‐haloacridines and their cross‐coupling reactions. Improved stability of several new compounds could be achieved by the synthetic modification at position 9 of the acridine unit compared to their unsubstituted acridine analogs. The basic spectroscopic characteristics of these useful intermediates were also determined. The new fluorescent compounds showed promising photochemical properties for optochemical‐based applications in the future. The extremely large Stokes‐shifts (above 15500 cm−1) should especially be emphasized. Moreover, the effects of the substituents at position 9 of the acridine unit on fluorescence signaling were studied by the examples of new precursors and their macrocyclic derivatives as known optical sensor molecules. Some interesting relationships between quantum yield and structural features were reported.
Lead is a particularly toxic heavy metal that is present above acceptable levels in the water of many countries. This article describes a quick detection method of lead(II) ions using a polyvinyl chloride (PVC)-based ion-selective membrane electrode containing an acridono-crown ether ionophore by potentiometry. The electrochemical cell exhibits a Nernstian response for lead(II) ions between the concentration range of 10−4 to 10−2 M, and can be used in the pH range of 4–7. The applicability of this sensor was verified by measuring a multicomponent aqueous sample. Under the given conditions, this electrode is suitable for the selective quantitative analysis of lead(II) ions in the presence of many additional metal ions.
New highly lipophilic enantiopure crown ethers containing a heterocyclic unit have been synthesized. Phase transport, UV-Vis- and fluorescence spectrophotometric investigations as well as electrochemical studies on the complexation of the new macrocycles with several amine and amino acid derivatives were also carried out. Achiral amines were used for studying the structural preference of the new macrocycles. Among the studied structural features of the guest molecules, the intermolecular π-π interaction showed the most significant effect on complexation, which made the aralkylamine-type compounds the most preferable guest molecules. The studied liquid membrane-based applications and photophysical investigations showed appreciable enantiomeric recognition toward some aralkylamine model compounds with homochiral preferences. New crown ether derivatives (R,R)-2 and (S,S)-2 were successfully applied as enantioselective carrier and sensor molecules.
Crown ethers containing an acridone or an acridine unit are successfully applied opto- and electrochemical cation sensors. The heteroaromatic unit of these macrocycles can be in different forms during the applications, which have a strong influence on the sensing behavior. Moreover, in the case of acridono-macrocycles a prototropic equilibrium takes place upon complexation, which is effected by the physicochemical characteristics. A Pb2+-selective acridono-18-crown-6 ether and its 9-phenylacridino-analogue were used as model compounds for comparing the different forms of the heterocyclic units of these sensor molecules. Since in most practical sensor applications of the fluorescent hosts a non-neutral aqueous medium is present, studies on complexation and signaling were carried out from the aspect of the relationship among protonation, coordinating ability, complex stability and tautomeric equilibrium. A strong interdependence among these factors was found and limitations of using unsubstituted acridino- and acridono-sensor molecules in comparison with their 9-substituted-acridino-analogues were discussed. This study will hopefully serve as a useful standpoint for future development of ionophore-based sensors containing an acridone or an acridine unit.
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