Intersystem crossing to both ligand-localized and charge-transfer excited states in mononuclear and dinuclear ruthenium(II) diimine complexes
- Tulane Univ., New Orleans, LA (USA)
The unsaturated bridging ligand 1,4-bis(2-(4{prime}-methyl-2,2{prime}-bipyrid-4-yl)ethenyl)benzene (dstyb) was prepared in a simple two-step sequence. The ruthenium complexes (((dmb){sub 2}Ru){sub n}(dstyb)){sup 2n+} (n = 1,2; dmb = 4,4-dimethyl-2,2{prime}-bipyridine) were prepared, and their redox and photophysical properties were examined. Both complexes have a single oxidation in cyclic voltammetry at 1.10 V vs SSCE, for the dinuclear complex n = 2. The first one-electron reductions are localized on the dstyb ligand and occur at {minus}1.32 and {minus}1.26 V for the mononuclear and dinuclear complexes, respectively. The emission maximum in room-temperature CH{sub 3}CN is 680 nm for ((dmb){sub 2}Ru(dstyb)){sup 2+} and 720 nm for (((dmb){sub 2}Ru){sub 2}(dstyb)){sup 4+}. For both complexes emission quantum yields are <0.05, and luminescence lifetimes are 622 ns for the monomer and 2.02 {mu} for the dimer at room temperature. The very low radiative decay rates ({psi}{sub em}/{tau}) observed result from low intersystem crossing efficiencies for population of the emitting {sup 3}MLCT state. Transient absorption spectra of the two complexes provide evidence for the presence of a {sup 3}({pi} {yields} {pi}*) state. In the mononuclear complex the lifetime of the T{sub 1}{yields}T{sub 2} absorbance of the {sup 3}({pi}{yields} {pi}*) state is 1.6 {mu}s, much longer than the emission lifetime. The {sup 3}MLCT emission and the {sup 3}({pi}{yields}{pi}*) absorption lifetimes of the dinuclear complex are within experimental error, indicating the states are equilibriated. Quenching of the transient absorbance with a series of triplet quenchers provides a measure of the triplet energy of the {sup 3}({pi}{yields}{pi}*) state of the complexes.
- OSTI ID:
- 7123367
- Journal Information:
- Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 112:3; ISSN 0002-7863; ISSN JACSA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360104* -- Metals & Alloys-- Physical Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500 -- Photochemistry
CHEMICAL REACTIONS
COMPLEXES
DATA
DATA ANALYSIS
ENERGY LEVELS
EXCITED STATES
EXPERIMENTAL DATA
INFORMATION
MEASURING INSTRUMENTS
MEASURING METHODS
NUMERICAL DATA
PHOTOCHEMICAL REACTIONS
REDOX REACTIONS
RUTHENIUM COMPLEXES
TRANSITION ELEMENT COMPLEXES
VOLTAMETRY