Theoretical Design of a New Allosteric Switch and Fluorescence Chemosensor Double Functional Devices of Aza-Crown Ether

A novel molecular device (trans-azobenzene embedded N-(11-pyrenyl methyl)aza-21-crown-7) with double functional devices was designed on the basis of theoretical calculations. Pyrenyl methyl covalently bonded to aza-21-crown-7 at the nitrogen position interacting with a series of alkaline-earth metal cations (Mg2+, Ca2+, Sr2+, and Ba2+) was investigated. The fully optimized geometries and real frequency calculations were investigated using a computational strategy based on density functional theory at B3LYP/6-31G(d) level. Free ligand (L) and their metal cation complexes (L/M2+) were studied using mixed basis set (6-31G(d) for the atoms C, H, O, and N and LANL2DZ for alkaline-earth metal cations Mg2+, Ca2+, Sr2+, and Ba2+. The natural bond orbital analysis that is based on optimized geometric structures was used to explore the interaction of L/M2+ molecules. The absorption spectra of L and L/M, excitation energies, and absorption wavelength for their excited states were studied by time-dependent density functional theory with 6-31G(d) and LANL2DZ. A new type of molecular device is found, which has the selectivity to Ca2+ and the emission fluorescence of L/Ca2+ under the condition of illumination. This molecular device would serve as an allosteric switch and a fluorescence chemosensor.