Our research focusses on the interaction of conjugated organic molecules in the solid state. There are two projects which investigate these interactions spectroscopically. Our first project measures the polarized absorption spectra of perylene diimide (PDI) derivatives.
The structure of PDI derivatives
By changing the side groups on PDIs, the unit cell of the molecular crystals can vary drastically. The molecular orientation in turn affects both the color of the crystals and their response to linearly polarized light. The two movies below show the color change of two different types of PDI crystals as a function of the electric field vector of incoming light. The molecule B2 has 3-pentyl pendant side chains, which are braced side chains. In contrast, C7 has n-hetyl side chains, which are linear side chains. The changes in the response to polarized light shown here have great implications on electron transport and mobility in organic electronic devices.
Our second project fabricates and measures the spectroscopic properties of thin films of poly(3-hexylthiophene) (P3HT) blended with PDI molecules. These films serve as precursors to active layers in organic photovoltaic systems. By varying the length of branched side chains on the PDI species, the composition of these blended films can change drastically compared to their casting solutions. The mechanisms behind the composition changes also relate to film heterogeneity and morphology, which are two important parameters in the optimization of photovoltaic efficiency in these materials.
