%0 Journal Article %1 Fees.1993 %A Fees, Joerg %A Kaim, Wolfgang %A Moscherosch, Michael %A Matheis, Walter %A Klima, Jiri %A Krejcik, Michael %A Zalis, Stanislav. %D 1993 %J Inorganic Chemistry %K bipyridine complex complex;ESR deriv electrochem pyridophenazine redox ruthenium %N 2 %P 166--174 %R 10.1021/ic00054a009 %T Electronic structure of the \dqmolecular light switch\dq bis(bipyridine)dipyrido3,2-a:2',3'-cphenazineruthenium(2+). Cyclic voltammetric, UV/visible and EPR/ENDOR study of multiply reduced complexes and ligands %V 32 %X The chelate ligand dipyrido3,2-a:2',3'-cphenazine (dppz), its 11,12-dimethyl deriv. (dmdppz), and corresponding complexes with Ru(bpy)22+ (bpy = 2,2'-bipyridine) were studied in multiply reduced states by low-temp. cyclic voltammetry and UV/visible and EPR spectroscopy. The (dm)dppz ligands were reduced in 2 reversible steps, followed by a moisture-sensitive 3rd step. Highly resolved EPR and 1H ENDOR spectra of the intermediate anion radicals were obtained and analyzed. The results were interpreted using a HMO/McLachlan perturbation approach of p spin populations and orbital energies. Three low-lying unoccupied p MOs can be identified as phenazine-type (b1, lowest) and as the y(b1) and q(a2) orbitals of the a-diimine moiety. Complexes with the N(4),N(5)-bound Ru(bpy)22+ fragment show $\geq$6 reversible 1-electron redn. steps in rigorously dried DMF at 200 K; the 1st 4 persistent reduced states were characterized by EPR and UV/visible spectroscopy. The EPR spectra of the 1st 3 reduced states of the complexes show a signal which proves the occupation of the phenazine-localized p* orbital of (dm)dppz by a single electron, the stepwise redn. of the bpy ligand resulting in temp.-dependent intensity loss of the EPR signal. The basic quadruply reduced state exhibits EPR characteristics which are typical for Ru(II)-bound a-diimine anion radicals. All assignments are supported by UV/visible spectra and analyses of redox potential values. Because the easily protonated higher reduced states are not sufficiently persistent for EPR and UV/visible characterization, further assignments could thus be based only on the anal. of redox potential values. The particular composite electronic structure of the complexes with differing redox and optical orbitals is related to their light switch behavior, i.e. to the absence of luminescence quenching in a nonaq. environment. on SciFinder(R)

@article{Fees.1993, abstract = {The chelate ligand dipyrido[3,2-a:2',3'-c]phenazine (dppz), its 11,12-dimethyl deriv. (dmdppz), and corresponding complexes with [Ru(bpy)2]2+ (bpy = 2,2'-bipyridine) were studied in multiply reduced states by low-temp. cyclic voltammetry and UV/visible and EPR spectroscopy. The (dm)dppz ligands were reduced in 2 reversible steps, followed by a moisture-sensitive 3rd step. Highly resolved EPR and 1H ENDOR spectra of the intermediate anion radicals were obtained and analyzed. The results were interpreted using a HMO/McLachlan perturbation approach of \textgreek{p} spin populations and orbital energies. Three low-lying unoccupied \textgreek{p} MOs can be identified as phenazine-type (b1, lowest) and as the \textgreek{y}(b1) and \textgreek{q}(a2) orbitals of the \textgreek{a}-diimine moiety. Complexes with the N(4),N(5)-bound [Ru(bpy)2]2+ fragment show $\geq$6 reversible 1-electron redn. steps in rigorously dried DMF at 200 K; the 1st 4 persistent reduced states were characterized by EPR and UV/visible spectroscopy. The EPR spectra of the 1st 3 reduced states of the complexes show a signal which proves the occupation of the phenazine-localized \textgreek{p}* orbital of (dm)dppz by a single electron, the stepwise redn. of the bpy ligand resulting in temp.-dependent intensity loss of the EPR signal. The basic quadruply reduced state exhibits EPR characteristics which are typical for Ru(II)-bound \textgreek{a}-diimine anion radicals. All assignments are supported by UV/visible spectra and analyses of redox potential values. Because the easily protonated higher reduced states are not sufficiently persistent for EPR and UV/visible characterization, further assignments could thus be based only on the anal. of redox potential values. The particular composite electronic structure of the complexes with differing redox and optical orbitals is related to their light switch behavior, i.e. to the absence of luminescence quenching in a nonaq. environment. [on SciFinder(R)]}, added-at = {2022-06-15T11:26:56.000+0200}, author = {Fees, Joerg and Kaim, Wolfgang and Moscherosch, Michael and Matheis, Walter and Klima, Jiri and Krejcik, Michael and Zalis, Stanislav.}, biburl = {https://puma.ub.uni-stuttgart.de/bibtex/2cc675ce597ecbc89bc22da5bba971822/huebleriac}, doi = {10.1021/ic00054a009}, interhash = {e60c6b09c32543018ec38d3ac2864738}, intrahash = {cc675ce597ecbc89bc22da5bba971822}, issn = {0020-1669}, journal = {Inorganic Chemistry}, keywords = {bipyridine complex complex;ESR deriv electrochem pyridophenazine redox ruthenium}, number = 2, pages = {166--174}, timestamp = {2022-06-15T09:26:56.000+0200}, title = {Electronic structure of the {\dq}molecular light switch{\dq} bis(bipyridine)dipyrido[3,2-a:2',3'-c]phenazineruthenium(2+). Cyclic voltammetric, UV/visible and EPR/ENDOR study of multiply reduced complexes and ligands}, volume = 32, year = 1993 }