Ultrafast Spectroscopic Study of Donor-Acceptor Light Harvesting Organic Conjugated PolymersPresenter: Bradley KellerNew light harvesting organic conjugated polymers(CP) containing 4,8-bis(2-ethylhexyloxy)benzo[1,2-b;3,4-b’]dithiophene(BDT) donor groups and thiophene(T) acceptor groups with various electron-withdrawing groups have garnered great interest for their high power conversion efficiencies (PCE).  One of the leading organic light harvesting CP, poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-bʹ]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7), has shown exceptionally high PCE making it an appealing material for solar cell applications.  Herein, we investigated new polymers with BDT donor groups and with thiophene acceptor groups with various electron-withdrawing groups using ultrafast spectroscopy in order to elucidate the spectroscopic and optical properties that contribute to high PCE light harvesting organic CPs.  The results show polymers with large dipole moments, large two-photon cross-sections, fast decay dynamics, and low quantum yields exhibited the best PCEs.   These properties may be useful in designing more efficient light harvesting CPs.   Rapid, Puncture-Initiated Healing via Oxygen-Mediated PolymerizationPresenter: Scott ZavadaAutonomously healing materials that utilize thiol–ene polymerization initiated by an environmentally borne reaction stimulus are demonstrated by puncturing trilayered panels, fabricated by sandwiching thiol–ene–trialkylborane resin formulations between solid polymer panels, with high velocity projectiles; as the reactive liquid layer flows into the entrance hole, contact with atmospheric oxygen initiates polymerization, converting the liquid into a solid plug. Using infrared spectroscopy, we find that formulated resins polymerize rapidly, forming a solid polymer within seconds of atmospheric contact. During high-velocity ballistics experiments, additional evidence for rapid polymerization is provided by high-speed video, demonstrating the immediate viscosity increase when the thiol–ene–trialkylborane resins contact atmospheric oxygen, and thermal imaging, where surface temperature measurements reveal the thiol–ene reaction exotherm, confirming polymerization begins immediately upon oxygen exposure. While other approaches for materials self-repair have utilized similar liquid-to-solid transitions, our approach permits the development of materials capable of sealing a breach within seconds, far faster than previously described methods.