Towards Materials for Solar Energy Conversions: Understanding Donor Group Effects on Electron Transfer in Substituted Paraphenylenes Darlene K. Taylor, Department of Chemistry North Carolina Central University We have examined 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. Targets: I II III a) b) Dimer Band gap (eV) IH-T* 4.59 IH-H‡ 4.55 IIH-T 3.74 IIIH-T 3.93 * , ‡: shown in figure at right where H-T denotes head-to-tail and H-H denotes head-to-head coupling LUMOI(H-T) LUMOI(H-H) HOMOI(H-T) HOMOI(H-H) The HOMO-LUMO band gaps were calculated by B3LYP with a polarized 6-31G(d) basis set.