Theoretical Study Fluorescent Chemosensor Based On Crown Ether Derivatives As Receptor

In this paper, the theory of quantum chemistry calculation has been carried out tostudy crown ether derivatives as receptor of the fluorescent chemosensor based onPET mechanism. The following three fluorescent chemosensor systems calculatedusing the DFT methodsFirstly, new calixarene derivatives pyrene-armed calix[4]azacrowns L (L1and L2)bearing a crown ether and an azacrown ether as two binding sites are calculatedsystemically using density functional theory (DFT). The optimized structures andelectronic properties, such as HOMO and LUMO energies, band gaps of the freeligands L (L1and L2), the complexes L/M+(Ag+, K+and Cs+) and the di-cationcomplexes L·Ag+·M+have been performed at B3LYP/6-31G(d) and Lanl2DZ level.Natural bond orbital (NBO) analysis is discussed on the basic of the optimizedgeometric structures. The results demonstrate that metal-π and metal-metal ionrepulsive interactions are main driving forces of the coordination and the influence ofthe solvent effect is significant. Moreover, the interesting “molecular taekowndo”processes evolving between Ag+-K+and Ag+-Cs+pairs have been studied through thefluorescence change. Time-dependent density functional theory (TD-DFT)calculations on the emission spectra of the ligand L1and compounds L1/M+areinvestigated and discussed, which further evidences the existence of the metal ionexchange process.Secondly, the fluorescence chemosensor methyl(9-methyl-anthracen)(N-ethylmonoaza-15-crown-5)amine (1) and methyl(9-methyl-anthracen)(N-ethylmonoaza-18-crown-6)amine (2) based on the Photoinduced Electron Transfer(PET) mechanism, in which anthracene acts as the fluorophore, dimethylethanamineas the linker, and monoaza-15-crown-5and monoaza-18-crown-6as the receptors aresuccessfully designed to detect Na+and K+ions by using Density Functional Theory(DFT) calculations. The proposed fluorescence chemosensors bound to the Na+andK+are performed by PBE, B3PW91,and B3LYP functionals with6-31+G(d,p) inacetone solvent. The calculated results of the HOMO and LUMO energies for thefluorophore and receptors using three functionals demonstrate that B3LYP suits to beused in calculating the relative molecular orbitals (MOs) energy levels. Additionally,the relative MO energies of fluorophore and receptors are not changed even thoughthey are linked mutually. It indicates that the MO energies of independent components can be utilized as the MO energies of chemosensors. The released energies of thecomplexation reaction suggest chemosensor (2) is more suitable for the formationstable complexes when binds to the Na+and K+.Thirdly, the logic gate (LG) are composed of three receptors: thebenzo-15-crown-5ether as receptor1for Na+, a tertiary amine as receptor2for H+, anda phenyliminodiacetate as receptor3for Zn2+. The geometry structures and vibrationalfrequencies of the free ligand LG, the complexes LG/Mn+(Mn+=H+, Na+and Zn2+),the di-cation complexes LG·M1n+·M2n+, and the complex LG·H+·Na+·Zn2+have beeninvestigated with the help of standard DFT methods with6-31G(d,p) as basis set. Thestability of those complexes has been analyzed using natural bond orbital (NBO)analysis. Time-dependent density functional theory (TD-DFT) calculations on theUV–Vis spectrum of the compounds LG/Zn2+, LG·Na+·Zn2+and LG·H+·Na+·Zn2+are recorded and the electronic properties such as HOMO and LUMO energies areperformed. The directly calculated ionization potential (IP), electron affinity (EA),electronegativity (χ), electrophilicity index (ω), hardness (η) and chemical potential (μ)are all correlated with the HOMO and LUMO energies with their molecularproperties.