Computational design of cucurbituril-acene hybrids for the optical detection of cesium ions: DFT and TD-DFT studies

Using density functional theory (DFT) calculations, we design a hybrid chemosensor obtained by combining the cucurbituril macrocycle with an aromatic acene moiety. The designed chemosensors are characterized by an optical response in the UV range between 180 nm and 300 nm that can be exploited for the optical detection of radioactive Cs-137 nuclides which are present in the contaminated soil and water as hydrated Cs+ ions. Upon binding the Cs+(aq) ion, time-dependent DFT calculations performed on the resulting complex indicate that some excitations are quenched and this provokes the disappearance from the absorption spectrum of a band located around 220 nm. On the other hand, the overall shape of the fluorescence spectrum seems not to be significantly affected by the complexation process except for a substantial increase in the intensity of the main emission band. The optical response of the complexes with Li+ ~ Rb+ is also investigated so as to assess the interference caused by these alkali metal ions, some of which (e.g., Na+, K+) are likely to be present in the contaminated environment.