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45702-GB10
Design and Systhesis of Core-Shell OptoElectronic Nanoparticles Based on Oligo(p-phenylene)s

Darlene K. Taylor, North Carolina Central University

Introduction
     World-wide photovoltaic production has increased 30% annually from 1997 to 2002 [1] with recent attention shifting from inorganic materials to solar cells based on flexible semiconductive organic materials [2].  Polymer-based solar cells exhibit 5% energy conversion efficiencies, far too low to compete with silicon photovoltaic or other renewable energy sources.  Various methods have been attempted to obtain increased energy conversion within the polymers, including altered polymer backbones, different molecular side chains, and polymer length. Despite an explicit paper by Iraqi et al., describing a relationship between polymer planarity and conductivity, few researchers have pursued planarity in efforts to maximize polymer conductivity [3].

     This investigation has focused on the effects of side chain substituent groups on the planarity and ultimately the electron transfer efficiency in paraphenylene dimers. These studies should be helpful as a crucial first step toward understanding the photophysics in organic semiconductor materials and could lead to the design of more efficient materials for the active layers in solar energy conversion devices. Major findings from this study are summarized below in this final report.

Results
     Synthesis and Characterization: Preliminary results on the synthesis of three paraphenylene dimers have been obtained: I) benzophenone; II) N,N-diethylamino benzophenone; and III) julolidinyl benzophenone.  The monomers were either purchased from Aldrich (I) or prepared by a modified version of a literature protocol [4]. The preparation was in general accomplished by reacting chlorinated benzoic acid with excess aniline at room temperature to yield a chlorobenzanilide derivative in about 98 % yield.  In the presence of phosphorous oxychloride, the desired organic donor (either N-diethylaniline or julolidine) interacts with the chlorinated carbonyl to yield 40% desired product after purification. The monomers were characterized by NMR, HPLC, and GC/MS prior to Ni(0) coupling that afforded the desired dimers.

     Computational: The dimer geometry predictions have been obtained through the NC High School Computational Chemistry Server (Gaussian B3LYP calculations).  A loss of planarity can be observed as the void space decreases due to an increase in side chain donor group bulkiness.  
The Cluster Computing Group at Earlham University provided access to WebMO where computational studies were continued to determine the HOMO-LUMO band gaps of the three dimers. The energies were calculated by B3LYP with a polarized 6-31G(d) basis set. Table 1 below reports the results where the band gap roughly decreases with more effective side chain donor groups.

Table 1. Summary of Computational Results

Dimer	Band gap (eV)
IH-Ta	4.59
IH-Hb	4.55
IIH-T	3.74
IIIH-T	3.93
a. H-T = Head-to-Tail; b. H-H = Head-to-Head

Participation of and Outcomes for Student Researchers
     One NC Central undergraduate was directly compensated with summer stipend from the grant. This undergraduate worked on the project part-time for two summer months.  In addition, a high school student contributed to the project for thirteen months (in exchange for academic research credit at his host institution) and one full summer term (supported by stipend directly from the ACS-PRF grant). This student was accepted to several undergraduate programs before deciding to attend Wake Forest University for Fall 2008.  His contribution to the project was the basis for: 1) a poster presentation by the PI at the 2008 SERMACS regional meeting as well as 2) the seed for a collaborative Center proposal recently submitted to the Department of Energy and lead by colleagues in the Chemistry Department at UNC-Chapel Hill.  Additional seed money has been attracted from NASA to support a new undergraduate student at NC Central to continue the preliminary findings reported herein.

References
1. Sariciftci, Niyazi Serdar, and Gilles Dennler. Proceedings of the IEEE 93.8 (2005): 1429-39.

2. Heeger, Alan J., and Maria A. Diaz-Garcia. Current Opinion in Solid State and Materials Science 3.1 (1998): 16-22.
3. Iraqi, Ahmed, George W. Barker, and David F. Pickup. Reactive and Functional Polymers 66.1 (2006): 195-200.

4. Taylor, D. K.; Samulski, E. T. Macromolecules  33 (2000): 2355-2358.

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