Polytetrahydrofuran cross-linked polystyrene resins for solid-phase organic synthesis

Currently, divinylbenzene cross-linked polystyrene (DVB-PS) is the polymer of choice for use in solid-phase organic synthesis (SPOS). While much research has been directed toward the optimization of linker groups for the attachment of compounds to the polymer, the development of new polymers themselves has been relatively neglected. In an attempt to overcome the shortcomings of DVB-PS and to develop new polymers with optimum properties for use in organic synthesis, we have prepared a series of polystyrene polymers that incorporate flexible polytetrahydrofuran (PTHF) based cross-linkers. The objective of incorporating PTHF into the polymers was to slightly increase the overall polarity of the polymer and thus render the resins more organic solvent-like. Since the degree to which a resin swells in and absorbs a particular solvent correlates to how well substrates attached to the polymer are solvated, we compared the swelling of our new resins to commercially available DVB-PS resins. In all cases, we found that our resins swelled to a much greater extent than do DVB-PS resins, and their use should therefore allow for SPOS reaction conditions that more closely mimic homogeneous solution-phase conditions. It was also found that the PTHF chain length of the cross-linker does not affect the level of swelling since all of our cross-linkers afford resins with comparable levels of increased swelling. Furthermore, we have examined the utility of our resins in directed ortho-metalation reactions and found that the increased swelling of our resins allows for isolation of reaction products in yields comparable to what is achieved using standard solution-phase conditions.link_to_subscribed_fulltex

Experiments towards size and dopant control of germanium quantum dots for solar applications

While the literature for the doping of silicon quantum dots (QDs) and nanocrystals (NCs) is extensive, reports of doping their germanium analogs are sparse. We report a range of attempts to dope Ge QDs both during and post-synthesis. The QDs have been characterized by TEM, XPS, and I/V measurements of SiO₂ coated QD thin films in test cells using doped Si substrates. The solution synthesis of Ge QDs by the reduction of GeCl₄ with LiAlH₄ results in Ge QDs with a low level of chlorine atoms on the surface; however, during the H₂PtCl₆ catalyzed alkylation of the surface with allylamine, to enable water solubility of the Ge QDs, chlorine functionalization of the surface occurs resulting in p-type doping of the QD. A similar location of the dopant is proposed for phosphorus when incorporated by the addition of PCl₃ during QD synthesis; however, the electronic doping effect is greater. The detected dopants are all present on the surface of the QD (<em>s</em>-type), suggesting a self-purification process is operative. Attempts to incorporate boron or gallium during synthesis were unsuccessful