Theoretical Research On Optical Chemical Sensors Based On Azo/thia-Crown Ether Derivatives

In the paper, the density functional theory(DFT) is used to calculate and research the three optical chemical sensors, aza/thia-crown ether derivatives, in theory.At first, two new intramolecular charge transfer(ICT) probes, aza-18-crown-6with a coumarin group(L), and their complexes with metal cations(Na+, K+, Mg2+,Ca2+) were studied using density functional theory(DFT). The optimized structures have been proved to be the minimal states without imaginary frequencies at B3LYP/6-31+G(d, p) level. Their structures and relevant parameters show the planarization between N in the crown ether ring and coumarin group from L to L/Mn+,which enhances the conjugation. The binding energies, enthalpies and Gibbs free energies of the complexes L/Mn+ have been calculated. Besides, natural bond orbitals(NBO) analysis indicates interaction between N and Mn+. Then time-dependent density functional theory(TD-DFT) calculations achieved the absorption spectra and partial excitation data, illustrating high selectivity for Ca2+.Then, another four acridizinium crown ether decivatives L1, L2, L3, L4 were studied using density functional theory(DFT) method. Firstly, we optimized the four free ligands and their complexes with Hg2+, Mg2+ in gas phase at B3LYP/6-31+G(d)basis level with the Lanl2 DZ method. And the subsequent analyses of natural bond orbitals(NBO) and absorption properties indicate that L3, L4 are affected severer by metal cations, and may show selectivity for ions. Then further research of the two systems has been done in acetonitrile and water using the polarizable continuum model(PCM), respectively. Moreover, in the UV-vis absorption spectra, only L3/Mg2+and L4/Hg2+ are distinct from other metal complexes, and appear obvious red-shift.Finally, two new benzo-crown ethers containing tetrathiafulvalene(TTF) unit(L1,L2) and their complexes with metal cations(Na+, K+, Ag+) were studied using density functional theory(DFT) method. Basing on their optimized structures, the binding energies and Gibbs free energies of the complexes confirm their stability in gas phase,and the natural bond orbital(NBO) analysis demonstrates the interaction between ligands and metal cations. Additionally, the 1H nuclear magnetic resonance(1H NMR)data indicate the selectivity for Ag+. And the decrease of the highest occupied molecular orbital(HOMO) energy levels of the complexes L1/K+, L2/Ag+, explains the anodic shift of the first oxidation potential in the cyclic voltammetrys(CVs) andthe high selectivity for K+, Ag+.