Oligothiophenes are of increasing interest in organic based electronic devices in part due to their high electron and hole mobilities. In an organic photovoltaic (OPV) device, the electronic properties of oligothiophenes make them advantageous as charge transfer junctions. To serve as charge transfer junctions, oligothiophenes must be functionalized to bind to the donor and acceptor parts of the device. The donor and acceptor parts are different materials and the synthesis of asymmetric oligothiophenes is of great interest. Previous researchers in our lab synthesized four asymmetric oligothiophenes, two with two thiophene subunits and two with four. Each set of oligothiophenes contained a pair of constitutional isomers. Here we report the synthesis of another asymmetric oligothiophene, one with three thiophene subunits. This compound is functionalized with bipyridine to bind Ru(bpy)22+ and with phosphonic acid moieties to bind CdSe nanoparticles. The synthesis was carried out by bonding a phosphonic acid moiety to bithiophene and bipyridine to thiophene and then coupling the phosphate-bithiophene and thiophene-bipyridine. Standard Stille couplings were used for carbon-carbon bond formation. The resulting compounds have complex NMR spectra and overlapping Ru MLCT and π-π* transitions at 450 nm with molar extinction coefficient on the order of 3 x 105 M-1 cm-1. The thiophene fluorescence is quenched by Ru(bpy)22+. These optical properties compare closely with the previous compounds synthesized. Solar cells occupy significant attention in the media, politics and science for their promise of continual pollution-free energy. Quantum dots, metal complexes and organic compounds are all under research as viable replacements for expensive silicon solar cells. To test the efficacy of a light harvesting compound before constructing a solar cell, a model system is constructed to show electron transfer from the light harvester into an electron acceptor. We synthesized oligothiophenes and oligothiophene-ruthenium complexes and tested their ability to act as sensitizers and charge transfer junctions. To do this, they were bonded to CdSe nanoparticles and their optical properties were measured. Steady-state photoluminescence and time correlated single photon counting were used to observe the effects on fluorescence and fluorescence lifetime of the CdSe-oligothiophene and CdSe-oligothiophene-ruthenium complexes before and after binding. It was found that CdSe fluorescence was quenched when bound to an oligothiophene ruthenium complex, and that the fluorescence of the oligothiophene was quenched when bound to CdSe in the absence of ruthenium. The fluorescence lifetimes of the quenched species were shortened.



College and Department

Physical and Mathematical Sciences; Chemistry and Biochemistry



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Oligothiophene, CdSe nanoparticle, Ruthenium