Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Chemistry, Inorganic

Date of Defense

8-8-2013

Graduate Advisor

Janet Braddock-Wilking, Ph.D.

Committee

Eike Bauer

Wesley R. Harris

Nigam P. Rath

Abstract

Siloles, or silacyclopentadienes and other group 14 metalloles are structurally analogous to their all-carbon analogue, cyclopentadiene, except for the heavy group 14 element (i.e., Si, Ge, Sn, and Pb) in the 1-position. The placement of the heavy element in this position allows for unique properties, such as high electron affinity, mobility, and bathochromically shifted optical spectra, as compared to cyclopentadienes, and the relatively low-lying lowest-unoccupied molecular orbital (LUMO) helps to account for these properties. The substituents about the silole have a significant impact on the electronics and properties observed, with 2,5-substituents inducing the most substantive changes. Even as many 2,5-substituents are known, and could possess potential to bind to metal cations, very few reports to date have studied metal binding effects on the optoelectronics of siloles. The goal of this investigation is to synthesize siloles with 2,5-substituents that could potentially coordinate metal centers, and study the optical changes upon addition of metal solutions. Several symmetric 2,5-substituted siloles were synthesized and characterized by various means, and showed modest to significant changes upon addition of metal centers. The most significant changes were observed with a p-dimethylaminophenyl substituted silole. The binding of this silole was studied in further detail through spectrophotometric titration, which suggested two binding events occurring at different locations on the silole. These studies also reveal the binding constant of the second, weaker binding event. The results of the studies suggest an appropriate explanation from the phenomenon of photoinduced-charge transfer, to which metal cations can significantly interfere, and helps to explain the changes in the spectral data observed. Additionally, the crystal structures of a series of germoles and germafluorenes have been acquired, and their packing affects with respect to potential for aggregation-induced emission studies are explored. The attempted synthesis of siloles with potential for “off-on” fluorescent behavior upon exposure to metals, as well as asymmetric 2,5-substituted siloles with coordinative ability, are also addressed, and briefly discussed.

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