Theoretical Study On The Switchable Nonlinear Optical Properties Of The Sandwich-type Ferrocene-based Complexes

Sandwich-type metal complexes have shown a potential application in the field of molecular recognition, catalysis, nano-composite, optics and biological sensors because of their unique electronic structures, magnetism and optical properties. At present, various types of sandwich-type metal complexes have been widely synthesized and theoretically discussed. As one of the most important sandwich-type metal complexes, ferrocene is the earliest discovered. With their unique property and high thermal and chemical stability, ferrocene derivatives have been widely applied in the field of information technology, especially in the nonlinear optics (NLO). However, theoretical and systematical study on the NLO switching of the sandwich-type ferrocene derivatives is still relatively limited. By external stimuli, such as redox, some of ferrocene derivatives can rotate around the symmetric axis and their structures can transform from centrosymmetric to noncentrosymmetric conformation reversibly. This will provide a possible for the realization of the true NLO switching. The so-called true NLO switching means that the NLO response is very big in the "ON" state, whereas the NLO response of "OFF" state is zero. Thus, using quantum chemistry method to select such NLO switching is significant. At the same time, the research of ferrocene derivatives offers sufficient reference model for the design of new molecules with efficient NLO switching and lays the foundation for the experimental synthesis and further NLO application. We expect that the present researches will provide guide for the experiments to find new NLO materials.This thesis mainly focuses on the study of bonding, redox and second-order NLO switching properties of the sandwich-type ferrocene derivatives. And it has the followings:1. We have investigated a series of ferrocene/fullerenes hybrid molecules by using density functional theory. These hybrid complexes through face-to-face fusion would enjoy the merits of both ferrocene and fullerene due to their strong donor-acceptor interactions. The absorption bands and first hyperpolarizabilities of these hybrid complexes are strongly sensitive to the carbon cage size, which is ascribed to a change in the charge transfer pattern. Especially for CpFe(C80H5), which displays reverse ???* charge transfer from bottom to top cage, leading to notable hyperpolarizability. The NLO properties of these hybrid molecules can change by adjusting the size of the fullerene carbon cage, which shows that these hybrid molecules have a great application prospect.2. In the tetrahydrofuran solution, a series of complexes that are comprised of ferrocene donor and various buckybowl acceptors with push-pull characteristics have been investigated. According to the computer results, these complexes show significant ?-? stacking interaction between buckybowl acceptors and their thermal and chemical stabilities are high. The electrochemical experiment suggests the possibility of the redox reaction. Upon redox action, these complexes show some important change of absorption spectra and second-order NLO properties. The redox switching ability suggests that these ferrocene-buckybowl complexes can be viewed as redox-triggered NLO switching with one of the complexes having an on/off ration of 100.3. We investigated a series of ferrocene derivatives by density functional theory, these derivatives are composed of constant ferrocene donor and 4,4'-bipyridiniurn acceptor and varied organic connectors. Result show that the conjugation of the organic connector can cause a significant increase in first hyperpolarizability and result in the molecular switching with large NLO contrast. The increase of the first hyperpolarizabilities for these ferrocene derivatives are mainly of ferrocene to 4,4'-bipyridinium charge transfer and the mixture of intramolecular charge transfer within the respective two 4,4'-bipyridinium coupled with interlayer charge transfer between two 4,4'-bipyridinium.4. On the basis of previous research, a series of ferrocene-based actuators with varied acceptor units have been systematically investigated. On the basis of the density functional theory, the hyperpolarizability is related to the acceptor units. Meanwhile, the open complexes are centrosymmetric and their first hyperpolarizabilities are zero. However, first hyperpolarizabilities of the closed complexes are very large due to their noncentrosymmetric conformation, which is related to the intramolecular interlayer charge transfer occurred between two respective acceptor units.