Bending crystals. Solid state photomechanical properties of transition metal complexes containing semiquinonate ligands |
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Authors: | Cortlandt G Pierpont |
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Institution: | (1) Department of Chemistry and Biochemistry, University of Colorado, 80309 Boulder, Colorado, USA |
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Abstract: | The properties of transition metal complexes containing catecholate and radical semiquinonate ligands have often been found
to be unusual and unexpected. Crystals of Rh(CO)2(3,6-DBSQ), containing the 3,6-di-tert-butyl-1,2-semiquinonate ligand, form as long thin needles that are observed to bend
reversibly upon irradiation with NIR light. Crystallographic characterization reveals a stacked solid state lattice with planar
molecules aligned with metal atoms atop one another. Electronic spectra recorded in the solid state and in solution show an
intense band at 1600 nm that maps the energy dependence of crystal bend angle. The transition is a property of the stacked
assembly, rather than of an individual complex molecule, and appears associated with an MLCT process that transfers charge
from an antibonding band formed by interacting Rhd
z
2
orbitals to the vacant quinone π* orbital. Related observations have been made on the Co(μ-pyz)(3,6-DBSQ)(3,6-DBCat)]npolymer. Photomechanical properties appear associated with electronic transitions that lead to a physical change in axial
length of a linear polymer, coupled with a soft solid state lattice that permits axial contraction/expansion without crystal
fracture. |
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Keywords: | Semiquinonate transition metal charge transfer photomechanicalproperty |
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