Bichromophoric Polysilane Heterocycles and Cages

Electron transfer processes play a central role in many areas of science such as in natural photosynthesis, where light absorption by appropriate antenna systems is followed by a series of energy and electron transfer steps in order to convert solar energy into chemical energy. Recently, researchers have paid much attention to artificial photosynthesis, what involves the mimicry of photosynthetic processes and the application of fundamental principles in photosynthesis to energy conversion systems and molecular devices like wires or switches at a molecular level. In this context electron transfer processes within various types of bichromophoric covalently linked donor-bridge-acceptor (D-br-A) compounds were studied and electronic coupling between D and A groups was found to primarily depend on the D/A distance and on the electronic properties of the bridge. So far, mainly carbon based frameworks were utilized as linkers in such D-br-A systems. Among the heavier main group element-catenated systems, however, especially the silicon based oligo- and polysilanes are likely to be potential bridges due to extensive delocalization of s-electrons along the silicon backbone. In fact, literature data available so far support the assumption, that electronic coupling of D/A substituent groups via oligosilanes can be a rather effective process especially in the case, when it is possible to control the conformation of the Si-Si skeleton in a desired manner. Within the current project, therefore, priorily unknown heterocyclic and cage like oligosilanes shall be synthesized using especially tailored synthetic strategies. Strong substituentsubstituent electronic coupling in these model compounds shall be realized by - using sterically rigid oligosilane spacers - carefully selecting the electronically active substituent groups and - incorporating substituents directly into the conjugation path. Furthermore, spectroscopic and electrochemical properties of the target compounds shall be investigated including computational studies in order to gain deeper insight into structural and electronic features.

Electron transfer processes play a central role in many areas of science such as in natural photosynthesis, where light absorption by appropriate antenna systems is followed by a series of energy and electron transfer steps in order to convert solar energy into chemical energy. Recently, researchers have paid much attention to artificial photosynthesis, which involves the mimicry of photosynthetic processes and the application of fundamental principles in photosynthesis to energy conversion systems and molecular devices like wires or switches at a molecular level. In this context electron transfer processes within various types of bichromophoric covalently linked donor-bridge-acceptor (D-br-A) compounds were studied. So far, mainly carbon based frameworks were utilized as linkers in such D-br-A systems. However, literature data available so far support the assumption, that silicon based oligo- and polysilane bridges might exhibit superior properties due to extensive delocalization of electrons along the silicon backbone especially in the case, when it is possible to control the conformation of the Si-Si skeleton in a desired manner. Within the current project, therefore, previously unknown heterocyclic and cage like oligosilanes were synthesized using especially tailored synthetic strategies. Spectroscopic and electrochemical properties of these model compounds, however, did not show exceptional substituent-substituent electronic coupling via the Si-Si bond system. A different situation was encountered, when double bonded fragments were incorporated into oligosilane cycles. Thus, for instance, UV spectroscopic features of cyclohexasilane derivatives with exocyclic Si=C double bonds, which also have been synthesized in the course of the project for the first time, indicated considerably enhanced electronic coupling. For the future, therefore, properties of considerable scientific interest can be expected for such and related species.