Voltammetry of Charge Transfer Light Absorbers

Cyclic Voltammetry of Charge Transfer Light Absorbers 

Electrochemistry is an analytical tool that can be used to determine redox potentials of an analyte as well as the fate of a molecule upon addition or removal of electrons. Of particular importance to photochemists is the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Cyclic voltammetry is one of the most commonly used electrochemical techniques and is based on the change in potential as a linear function of time. An electrochemical reaction is reversible if = 1 and AEp = 59/n mV, where ip is the anodic peak current, ip is the cathodic peak current, and A p (AE), = A p — Ep ) is the potential peak separation for the anodic ( ), ) and cathodic Ep ) peaks. The oxidation or reduction potential for a reversible electrochemical process is given by 1/2 = Ep + Ep jl and is recorded vs. a reference electrode. All electrochemical data provided herein are converted to V vs. saturated calomel electrode (SCE) to make the comparison more facile. A reversible redox couple implies that the complex undergoes facile electron transfer with the electrode and that no chemical reaction follows the electrochemical step. 

If a chemical reaction follows an electrochemical step, the cyclic voltam-mogram is typically irreversible and i jip 1 and/or A p 59/n mV. Cyclic voltammetry can be used to estimate the relative energy of the frontier orbitals of a series of complexes for each coordination site. A cyclic voltammogram for [Os(bpy)3] shows a reversible oxidation with 1/2= 0.81 V and three reversible reductions starting at —1.29 V. The oxidation is representative of Os , while the reduction represents sequential bpy for each coordinated ligand. The electrochemistry shows that frontier orbitals of [Os(bpy)3] involve an osmium-based HOMO and a bpy-based LUMO. This is consistent with the photochemical properties of [Os(bpy)3] in which the lowest energy 

SUPRAMOLECULAR COMPLEXES COUPLING Ru(II) OR Os(II) POLYAZINE LIGHT ABSORBERS AND Rh(III) REACTIVE METAL CENTERS 

The electrochemical and photophysical properties of a variety of mixed-metal supramolecular complexes incorporating Ru(II)/Os(II)-polyazine LAs to reactive Rh(III) systems have been investigated. The coupling of Rh(III) to ruthenium and osmium chromophores has been explored in some detail due to the known energy and electron transfer quenching of MLCT states of ruthenium and osmium by Rh(III) complexes in bimolecular processes. The systems studied to date most frequently included tris(bidentate) or bis(tridentate) coordination on Rh(III). While these studies provide considerable insight into the intramolecular excited state dynamics, these coordination environments typically prevent reactivity at the rhodium site. 

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E. Cyclic Voltammetry of Charge Transfer Light Absorbers 308... 

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