Optical and electrochemical properties of shell-core dendrimers: ruthenium coordination complexes capped with sized phenothiazine-substituted bipyridines.
A family of ruthenium coordination compounds capped by 4,4'-dimethylbipyridine ligands bearing 0, 1, 2, and 3 generations of dendritic phenothiazine moieties exhibit size-dependent electrochemical properties and structure-dependent absorption and luminescence spectra. Emission quantum yields, photoluminescence decay kinetics, and transient absorption spectra varied roughly with dendrimeric size and complexity on timescales from subnanoseconds to milliseconds. All complexes exhibit microsecond-lived lowest lying metal-to-ligand charge transfer excited states. Luminescence spectra were broadened compared with the unsubstituted parent, and quantum yields of emission for the large dendritic clusters were reduced by factors of two to five. Although the observed decay kinetics were complex, one transient decayed rapidly on a nanosecond scale, and a second intermediate showed no decay over a time scale of several tens of nanoseconds. Transient absorption measurements showed ground-state bleaching in regions of high ground-state absorptivity by the metal-to-ligand charge-transfer transient, as well as transient absorption shifts characteristic of isolated phenothiazine and ruthenium bipyridyl moieties.
Zhu
Linyong
L
Department of Chemistry and Biochemistry, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093-0358, USA.
Magde
Douglas
D
Whitesell
James K
JK
Fox
Marye Anne
MA