Research

Research in our group involves materials chemistry. Both inorganic and organic materials are synthesized and studied. Our main interest is in materials with novel electronic and magnetic properties.

Organic molecules in unusual oxidation states. Our investigations of dopants for organic molecular semiconductors have led to the synthesis and isolation of number of unusual or unique molecules. For example, we have isolated the first antiaromatic porphyrin complex, Si(TPP)(THF)₂, shown in Figure 1. It is a reduced, 20 pi-electron system, with alternating single and double bonds, highlighted in blue. In addition, we have synthesized an “extended viologen” that is the most reducing neutral organic molecule known, shown in Figure 2.

New Semiconducting Materials. Inorganic. We have synthesized several members of a new class of materials, metal-sulfur-organic networks. Their crystal structures have been determined either by single-crystal X-ray diffraction or synchrotron X-ray powder diffraction. Some of these materials are semiconducting: an example is [Pb₃(C₆S₆)]_n, shown in Figure 3. Organic. While a large number of 1-dimesional conjugated polymers are known, 2-dimesional conjugated materials are essentially unknown. A graphene sheet is one example. We have synthesized new graphite-like 2-dimensional conjugated materials, and the physical properties of those materials are being studied.

Composite Solar Cells. While solar cells with good energy-conversion efficiency are currently available, their price relative to other forms of energy production has limited their widespread application. Less expensive solar cells can be produced by using a direct-bandgap semiconductor such as CdTe (rather than indirect-bandgap Si) and solution-phase deposition of the active materials (rather than high-temperature crystal growth of Si). We are investigating a method that combines particles of a semiconductor such as CdTe with an organic ionic polymer to create a composite that will function as the active layer of inexpensive solar cells.

Selected Publications

• “An Antiaromatic Porphyrin Complex: Tetraphenylporphyrinato(Silicon)(L)₂ (L = THF or Pyridine)”, Cissell, J. A.; Vaid, T. P.; Rheingold, A. L., J. Am. Chem. Soc. 2005, 127, 12212-12213.
• “Synthesis and Characterization of a Highly Reducing Neutral ‘Extended Viologen’ and the Isostructural Hydrocarbon, 4,4’’’’-Di-n-octyl-p-quaterphenyl”, Porter, W. W., III; Vaid, T. P.; Rheingold, A. L., J. Am. Chem. Soc. 2005, 127, 16559-16566.
• “Reversible Oxidation State Change in Germanium(tetraphenylporphyrin) Induced by a Dative Ligand: Aromatic Ge^II(TPP) and Antiaromatic Ge^IV(TPP)(pyridine)₂”, Cissell, J. A.; Vaid, T. P.; Yap, G. P. A., J. Am. Chem. Soc. 2007, 129, 7841-7847.
• “Semiconducting Lead-Sulfur-Organic Network Solids”, Turner, D. L.; Vaid, T. P.; Stephens, P. W.; Stone, K. H.; DiPasquale, A. G.; Rheingold, A. L., J. Am. Chem. Soc. 2007, 129, ASAP.