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Nitrile-based carotenoid complexes of Ru (II), Re (I) and Pt (II) metals: Coordination synthesis, electrochemical and photophysical characterization
Cruz, Arvin John Filoteo
Cruz, Arvin John Filoteo
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Dissertation
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2009-12
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Abstract
Nitrile-based carotenoid complexes of Ru(II), Re(I) and Pt(II) metal ions have been synthesized.
The photolability of two bis-nitrilo ruthenium(II) complexes formulated as [Ru(bpy)₂(L)₂](PF₆)₂,
where bpy is 2,2’-bipyridine and L = acetonitrile and succinonitrile have been investigated. The
UV/visible absorption spectrum of the sn derivative is dominated by an intense (εmax~58700M⁻¹ cm⁻¹) absorption band at 287 nm assigned as a LC (∏ → ∏*) transition. The peak observed at
418 nm (ε ~ 10400 M⁻¹ cm⁻¹) is an MLCT band while the one at 244 nm (ε ~ 23600 M⁻¹ cm⁻¹) is
of LMLCT character. The AN derivative behaves similarly. These Ru(II) complexes undergo
photosubstitution of solvent with quantum efficiencies near one. Calculated and experimental
results support a stepwise replacement of the nitrile ligands. Based on DFT calculations, the
electron density of the HOMO lies on the metal center, the bipyridine ligands and the nitrile
ligands and electron density of the LUMO resides primarily on the bipyridine ligands. Ligand
pyridyl-cyano and dicyano derivatives of all-trans-retinal and β-apo-8’-carotenal have been
synthesized via Knoevenagel Condensation. Density Functional Theory and Time Dependent
Density Functional Theory calculations in all these ligand compounds reveal that the HOMO and
LUMO are located primarily on the polyene chain and the energy gap between them is consistent
with the observed optical spectrum. Spectroscopic treatments establish that their light-harvesting
properties are similar to those observed pigment-protein complexes in plants and purple bacteria
These observed properties are due to the highly allowed population of the second-lying ¹Bu
excited state. These compounds contain an electron pair donor and can be coordinated to
rhenium (I) and platinum (II) metal ion centers. These complexes are photosensitizer dyes in
dye-sensitized solar cells (DSSC’s) and also serve as photocatalysts and metallointercalators in DNA.
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Thesis (Ph.D.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry
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Wichita State University