Photochemical, photophysical and structural studies of complexes of ruthenium(II) and copper(I) with heteroaromatic chelating ligands
Abstract
Photophysics and photochemistry of ruthenium (II) polypyridyls and copper (I) phenanthrolines are herein investigated. The complex (Ru(trpy)(bpy)CH$\sb3$CN) $\sp{2+}$ exhibits photophysical behavior very similar to that of Ru(trpy)$\sb2\sp{2+}$; the observed activation barrier between the $\sp3$MLCT and $\sp3$LF states in solution is found to be 1560 cm$\sp{-1}$, versus 1500 cm$\sp{-1}$ for the homoleptic complex. Studies of the complexes doped into polymethylmethacrylate film indicate that these complexes may lose access to the $\sp3$LF excited state in rigid matrices. In the crystalline state, the picture is more complex and may be anion-dependent. The mixed-ligand complex, when irradiated in the MLCT absorbance region in CH$\sb3$CN at 25$\sp\circ$C in the presence of 1M pyridine, 4-phenylpyridine, or 2-picoline, gives clean substitution at the monodentate site, with photochemical quantum yields of.00131,.00127, and.00264, respectively. This result indicates a dissociative mechanism and puts to rest previous doubts about the photochemistry of Ru(II) polypyridyls based on other studies of the substitution mechanism of $d\sp6$ octahedral complexes in the literature which may have been confounded by chelation, solvento intermediates, secondary photolysis, ion pairing, or nucleophile-solvent side reactions. Also in support of this conclusion is the lack of photochemistry from the analogue (Os(trpy)(bpy)CH$\sb3$CN) $\sp{2+}$. Like Ru(II) polypyridyls, the copper (I) phenanthroline Cu(dpp)$\sb2\sp+$ also possesses a MLCT excited state, which is both a better reductant and a better oxidant than the ground state. Lifetime quenching experiments with a series of substituted ferrocenes provide the first direct evidence of the latter fact in a Cu(I) phenanthroline, and imply a self-exchange rate constant for the *Cu(dpp)$\sb2\sp{+/0}$ couple of approximately 1.5 $\times$ 10$\sp5$ M$\sp{-1}$s$\sp{-1}$. The energy-transfer quenching constant for Cu(dpp)$\sb2\sp+$ with ferrocenes at 23$\sp\circ$C is estimated at 8.83 $\times$ 10$\sp7$M$\sp{-1}$s$\sp{-1}$.
Degree
Ph.D.
Advisors
McMillin, Purdue University.
Subject Area
Chemistry|Chemistry
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