Michael Ziebel Summer 2014 Urg Final Report a Supramolecular Polymer for Organic Photovoltaic Devices

نویسنده

  • Michael Ziebel
چکیده

Organic photovoltaics (OPVs) represent a potentially low-cost solution for harnessing solar energy and addressing global energy needs. 1 Organic photovoltaics can be broken down into two categories: polymer solar cells and small molecule solar cells. Polymer solar cells have so far achieved higher efficiencies because they typically exhibit superior device architecture compared to those of small molecules. 2 However, small molecules remain interesting because they can be more easily functionalized to modify their electronic properties. 3 An ideal electron donor would merge the improved morphology of polymers with the tunability of small-molecules. One possible solution to this end would be the use of a chain-end functionalized supramolecular polymer. My research this summer has focused on the development of a supramolecular polymer to be incorporated into OPV devices. The initial synthetic scheme is shown in Figure 1. The target molecule 2 utilized a ureidopyrimidinone end-unit to induce end-to-end interactions. The ureidopyrimidinone unit was chosen both because it demonstrates self-recognition and because its multiple hydrogen bonds should produce the desired directionality. This synthetic pathway ultimately proved to be infeasible, as the desired bromination at the methyl position of the pyrimidinone does not take place. The bromination was attempted with and without light and heat, using both molecular bromine and N-bromosuccinimide, but only bromination at the 5-position (alpha to the carbonyl) was observed to occur. Because the phosphite group cannot be added to the 5-position, it was impossible to proceed with the desired Horner-Wadsworth-Emmons olefination. An alternative, but similar, ureatriazine end-unit was chosen for the second target molecule (5 in Figure 2). Like the ureidopyrimidinone moiety, the ureatriazine unit demonstrates multiple hydrogen bonds and self-recognition. The synthesis first converted 5-bromo-2-thiophenecarboxaldehyde to 5-bromo-2-thiophenecarbonitrile. This molecule was reacted with dicyandiamide to form a 1,3,5-triazine with two free amines. By reacting this molecule with hexyl isocyanate, ureatriazine 4 was synthesized. This molecule was expected to be soluble in a variety of organic solvents, similar to the ureidopyrimidinone unit. Unfortunately, 4 was only observed to be soluble in DMSO or warm polar solvents. It was hoped that solubility could be achieved by attaching the end-units to a benzodithiophene (BDT) core with two ethyl-hexyl solubilizing tails. The ureatriazine end-units were attached to a stannylated BDT molecule via a Stille coupling. The solution turned from yellow to red overnight, suggesting an extension of the conjugation and a successful reaction. The collected product was observed to be slightly soluble in …

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تاریخ انتشار 2014