Pushpull Alternating and Hypercoordinate Asymmetrical Architectures for Light and Moisture Stable Polystannanes
Department of Chemistry and Biology
Room: C2-361 (Reading Room)
Host: E. Fillion
Polystannanes, organometallic polymers consisting of an all tin backbone, were first successfully prepared in the early 90’s. These intriguing materials are intrinsic semiconductors and display a s-s* low energy transition in the visible and are effectively delocalized along the tin backbone. Unfortunately, the majority homopolystannanes suffer from an extreme sensitivity to visible light and moisture, and undergo rapid decomposition. To address these shortfalls and find paths to light and moisture stable polystannanes that could function as polymeric wires or as interconnects in printable electronics, we have recently explored three design approaches. The first is the self-catalyzed stoichiometric polycondensation reaction of tin dihydrides and tin diamides under mild reaction conditions that yield the alternating polystannanes (1). The simplicity of the chemistry affords the opportunity to build electronically tuned push-pull polystannanes, where alternating tin centers donate or withdraw electron density along the backbone. We have also prepared the first examples of asymmetrical polystannanes bearing 5-coordinate tin centers with both flexible and rigid hyper-coordination features. These polystannanes possess datively bonding oxygen or nitrogen centers that provide additional electron density to the backbone and can also function as light antennae (2) and (3). The datively interacting ligands also likely increase steric hindrance at tin and further protect the sensitive Sn-Sn bonds from nucelophilic attack. These design features have dramatically improved the light stability of polystannanes from minutes to over several months in the solid and solution state. The hypercoordinated polystannanes also demonstrate a much improved moisture stability compared to homopolystannanes.