Orange emitting fluorescence probe for the selective detection of cyanide ion in solution and solid states

Abstract Designing fluorescent molecular probes with longer wavelength emission (above 600 nm) features towards exclusive detection of CN − ion is highly challenging and rarely found in the field of fluorescent sensors. The contribution here reports a unique chemodosimetric design approach for selective sensing of CN − ion, in both solution and solid states. Towards this, we have utilized an orange emitting fluorescent probe ( R1 ) (λ  emission  > 600 nm), where the fluorophore is threaded by a fluorene derivative. The bulky fluorine unit regulate the interaction between the fluoropore units to minimize aggregation caused quenching (ACQ). Upon introducing CN − ion, even in the presence of several other ions, intramolecular charge transfer (ICT) from the donor (phenothiazine) to the acceptor (cyanovinyl unit) was completely blocked in the covalently threaded fluorescent moiety and as a result the fluorescence was completely quenched. More importantly, the present system retained its fluorescence properties in the solid state and hence was utilized to detect CN − ion in the solid state through fluorescence quenching mechanism, which enabled the fabrication of a test kit for on-site analysis of CN − ion. DFT and TD-DFT calculations towards validating the experimental results were also performed in order to study the changes caused in the electronic properties of R1 before and after complexation with CN − ion.