Synthesis and fluorescence studies of novel bis(azacrown ether) type chemosensors containing an acridinone unit

Three new bis(azacrown ether)s containing an acridinone fluorescent signalling unit were prepared by reacting 9-chloro-4,5-bis(chloromethyl)acridine with monoazacrown ethers with different cavity sizes followed by a hydrolysis step. Their fluorescent characteristics and the complexation properties of the one containing two monoaza-18-crown-6 ether receptors towards selected metal ions were studied. The operation of the latter ligand is based on the photoinduced electron transfer (PET) process, thus it shows fluorescence enhancement in the presence of metal ions. Since the sensor molecule contains two receptor moieties, it is able to form two types of complex with 1:1 and 1:2 ligand to metal ion ratios, which have different emission spectra. The reason for this spectral difference may be that the 1:1 complex is a sandwich type one in which the acridinone unit can undergo structural changes.