Crystalline Alloys of Organic Donors and Acceptors Based on TIPS-Pentacene

Co-crystals of organic semiconductors can provide model systems for the study of fundamental optoelectronic properties and also new functionality. 6,13-Bis­(triisopropylsilylethynyl)­pentacene (TIPS-Pn) and its fluorinated analogue 1,2,3,4,8,9,10,11-octafluoro-bis­(triisopropylsilylethynyl)­pentacene (F8TIPS-Pn) form crystalline substitutional alloys during bulk crystal growth from solution. Alloys can also be formed by blade casting thin films from solution. The compounds appear to have sufficient geometric similarity to be miscible in all proportions without inducing long-range disorder in the solid state. The offsets of the electronic levels of TIPS-Pn and F8TIPS-Pn in pure form are similar to those found in bulk heterojunction solar cells. UV/vis spectroscopy and density functional theory demonstrate the charge transfer absorption in the alloy crystals corresponds to an excitation across molecular pairs

Gelation Chemistries for the Encapsulation of Nanoparticles in Composite Gel Microparticles for Lung Imaging and Drug Delivery

The formation of 10–40 μm composite gel microparticles (CGMPs) comprised of ∼100 nm drug containing nanoparticles (NPs) in a poly­(ethylene glycol) (PEG) gel matrix is described. The CGMP particles enable targeting to the lung by filtration from the venous circulation. UV radical polymerization and Michael addition polymerization reactions are compared as approaches to form the PEG matrix. A fluorescent dye in the solid core of the NP was used to investigate the effect of reaction chemistry on the integrity of encapsulated species. When formed via UV radical polymerization, the fluorescence signal from the NPs indicated degradation of the encapsulated species by radical attack. The degradation decreased fluorescence by 90% over 15 min of UV exposure. When formed via Michael addition polymerization, the fluorescence was maintained. Emulsion processing using controlled shear stress enabled control of droplet size with narrow polydispersity. To allow for emulsion processing, the gelation rate was delayed by adjusting the solution pH. At a pH = 5.4, the gelation occurred at 3.5 h. The modulus of the gels was tuned over the range of 5 to 50 kPa by changing the polymer concentration between 20 and 70 vol %. NP aggregation during polymerization, driven by depletion forces, was controlled by the reaction kinetics. The ester bonds in the gel network enabled CGMP degradation. The gel modulus decreased by 50% over 27 days, followed by complete gel degradation after 55 days. This permits ultimate clearance of the CGMPs from the lungs. The demonstration of uniform delivery of 15.8 ± 2.6 μm CGMPs to the lungs of mice, with no deposition in other organs, is shown, and indicates the ability to concentrate therapeutics in the lung while avoiding off-target toxic exposure

Polling booth survey sample coverage of key populations in each study site across Kenya.

<p>Polling booth survey sample coverage of key populations in each study site across Kenya.</p