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Reed Group Research

The chemistry of multiply bonded dimetal paddlewheel complexes, of which a general structure is shown in Figure 1, has been of interest since the discovery of multiple bonds between metal atoms nearly 50 years ago.1-3 Dimetal paddlewheel complexes are not only interesting in their reaction chemistry4, but they have also found application in a myriad of areas, including: supramolecular assemblies for gas storage and separation5; molecular memory devices6; as well as photon harvesters, charge carriers, and light emitters in photovoltaic and light emitting devices.7-11


Figure 1.

The general structure of a dimetal paddlewheel complex has bridging equatorial ligands linked to metal centers by nitrogen, phosphorous, oxygen, or sulfur atoms (red). Depending on the oxidation state of the metal and bulkiness of equatorial ligands, axial ligands or solvent may also coordinate (green).

The importance of research in the area of cost-effective, energy-efficient photovoltaics is becoming ever more apparent as the energy demands of the planet increase. One avenue available for achieving more affordable photovoltaics is through the use of small molecule dyes for photon harvesting rather than silicon.12,13 This reduces material costs as well as alleviates the expensive purification process necessary to produce crystalline silicon wafers.14

We are interested in studying the photophysical and electronic properties of Re2(III,III) paddlewheel complexes to determine their potential for use as dyes in photovoltaic devices. Molybdenum and tungsten paddlewheel complexes have been investigated for use as photosensitizers in dye-sensitized or bulk-heterojunction solar cells7,10,11 however, rhenium analogs have been largely ignored. The rhenium analogs may prove to be more useful in devices due to the strikingly different energy of the metal based orbitals compared to molybdenum and tungsten. These rhenium paddlewheel complexes can be synthesized using standard air-free techniques and the photophysical and electronic properties can be evaluated using UV-vis, emission, and transient absorption spectroscopies as well as electrochemistry.

References

(1) Bertrand, J. A.; Cotton, F. A.; Dollase, W. A. J. Am. Chem. Soc. 1963, 85, 1349-1350.
(2) Bertrand, J. A.; Cotton, F. A.; Dollase, W. A. Inorg. Chem. 1963, 2, 1166-1171.
(3) Robinson, W. I.; Fergusson, J. E.; Penfold, B. R. Proc. Chem. Soc. 1963, 1963, 116.
(4) Cotton, F. A.; Murillo, C. A.; Walton, R. A. Multiple bonds between metal atoms; 3rd ed.; Springer, 2005.
(5) Koberl, M.; Cokoja, M.; Herrmann, W.; Kuhn, F. Dalton Trans. 2011, 40, 6834-6859.
(6) Lin, C.; Kagan, C. R. J. Am. Chem. Soc. 2011, 125, 336-337.
(7) Alberding, B. G.; Chisholm, M. H.; Gallucci, J. C.; Ghosh, Y.; Gustafson, T. L. PNAS 2011, 108, 8152-8256.
(8) Bunting, P.; Chisholm, M. H.; Gallucci, J. C.; Lear, B. J. J. Am. Chem. Soc. 2011, 133, 5873-5881.
(9) Lear, B. J.; Chisholm, M. H. Inorg. Chem. 2009, 48, 10954-10971.
(10) Alberding, B. G.; Chisholm, M. H.; Ghosh, Y.; Gustafson, T. L.; Liu, Y.; Turro, C. Inorg. Chem. 2009, 48, 8536-8543.
(11) Burdzinski, G. T.; Chisholm, M. H.; Chou, P.; Chou, Y.; Feil, F.; Gallucci, J. C.; Ghosh, Y.; Gustafson, T. L.; Ho, M.; Liu, Y.; Ramnauth, R.; Turro, C. PNAS 2008, 105, 15247-15252.
(12) O'Regan, B.; Gratzel, M. Nature 1991, 353, 737-740.
(13) Shaheen, S. E.; Ginley, D. S.; Jabbour, G. E. MRS Bull. 2005, 30, 10-19.
(14) Gratzel, M. J. Photochem. Photobiol. A. 2004, 164, 3-14.