| Metal complexes have aroused extensive attention for a variety of application fields since such species have unique photophysical and photochemistry properties. For example, Mn nitrosyls owning the capability of releasing NO upon exposure to visible or near infrared light could be potential candidate for photodynamic therapy (PDT) in experiment, which is significant for human. Since [Au(CN)2]nn-(n=1-3) oligomers has aurophilic interactions between Au(I) atoms and excimer photoluminescence behavior in the experiment, oligomers could be an important candidate for biosensors, photosensitizers, and optical sensors. Structural and excited states properties of such metal complexes were calculated by density functional theory (DFT) and time dependent density functional theory (TDDFT) to give a detailed and warranted explanation of the photodissociable and excimer emission mechanism in this work, major work as follows:(1)Structural, spectroscopic and photodissociable properties of series of Mn(II) complexes (a-d) were inverstigated by DFT to illuminate the mechanism of the performance of releasing NO. The results indicate that for a-d, releasing NO attributes to the electron transfer from dyz/dxz(Mn) orbitals to π*(NO) orbitals at the second excited triplet state (T2). Importantly, we confirmed the report in experiment that d could release NO upon exposure to NIR region, thus may be a best candidate for PDT in a-d. Therefore, to take d for example, the analyses of the potential energy curves (PECs) of difference states and electron density difference between the T2and the ground state (So) were performed to further provide evidences of ligand dissociation and releasing NO at the T2state. Finally, we hope that our discussion can provide assistance to understand the behavior of releasing NO and design novel photodissociable transition metal nitrosyls for PDT applications.(2)The structures of [Au(CN)2]nn-(n=1-3) oligomers in the ground state (So) and lowest triplet excited state (T1) were calculated by using the double hybrid B2PLYP functional as well as ab initio wave function theory calculation at the coupled-cluster level with single and double (CCSD) and the second-order M(?)ller-Plesset perturbation (MP2). The calculated results indicate that MP2and unrestricted MP2(UMP2) were successfully used to optimize the So and T1structures of staggered and eclipsed [Au(CN)2]22-and [Au(CN)2]33-, respectively. In addition, a large reduction (ca.10-12%) of the Au-Au bond lengths of [Au(CN)2]22-and [Au(CN)2]33-on going from the So to T1reveals the Au-Au interaction is strongly enhanced in the T1compared with that in the So. Then, the PECs results confirm that the stronger Au-Au interaction in the T1relative to the So plays a very important role of the formation of*[Au(CN)2]nn-excimer, since both of the lowest singlet excited states and T1of [Au(CN)2]22-and [Au(CN)2]33-have a deeper potential well. Finally, the analysis of the influence of spin-orbit coupling on the electron transition nature was performed in the T1of [Au(CN)2]nn-(n=1-3) oligomers. The results provide evidence that metal center and metal-metal-to-ligand charge transfer (MC and MMLCT) transition characters play an important role in the red-shift of the emission wavelength and the formation of*[Au(CN)2]nn-excimer at the T1. |
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