Syntheses, Spectroelectrochemistry and Photoinduced Electron-Transfer Processes of Novel Ru and Os Dyad and Triad Complexes with Functionalized Diimide Ligands

2001 ◽  
Vol 66 (2) ◽  
pp. 307-337 ◽  
Author(s):  
M. Delower Hossain ◽  
Masa-aki Haga ◽  
Bobak Gholamkhass ◽  
Koichi Nozaki ◽  
Minoru Tsushima ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Exponential Decay ◽  
Intramolecular Electron Transfer ◽  
Time Resolved ◽  
Mlct Transition ◽  
Ligand Charge Transfer ◽  
Back Electron Transfer ◽  
Donor Acceptor ◽  
Ru Complexes ◽  
Electron Transfer Processes

A series of mono- and dinuclear Ru complexes containing a bridging ligand, L-diimide-L (L = 2-(2-pyridyl)benzimidazole; diimide = benzene-1,2:4,5-bis(dicarboximide) (bdi; pyromellitimide) or naphthalene-1,8:4,5-bis(dicarboximide) (ndi), with either propane or xylene group as linkers, have been prepared. The mono- and dinuclear Ru complexes containing the bdi or ndi ligand, exhibit characteristic metal-to-ligand charge transfer (MLCT) transition at 458 nm. The mono- and dinuclear Ru/Os complexes exhibit a rich redox chemistry arising from both M(II) to M(III) oxidation and ligand-based consecutive reduction of diimide and 2,2'-bipyridine (bpy) ligands. The emission decays fit well with double- or triple-exponential decay models. The non-exponential decay curve reveals the existence of several conformers in solution due to the flexible propane or p-xylene linker. The much shorter emission lifetimes of the [M(bpy)2(L-diimide-L)] complexes compared with the parent [M(bpy)2L] indicates the intramolecular electron-transfer from the excited M(bpy)2 moiety to the diimide. The fastest rates of electron transfer (3 · 1010 s-1) are attributable to the folded conformers suitable for the electron donor/acceptor through-space interaction. A time-resolved absorption spectroscopic study of the dinuclear bdi and ndi complexes revealed appearance of the electron-transfer products, M(III) and the diimide radical anion, and their rapid disappearance. The effect of the linkers of the ligand L-diimide-L on the rates of electron transfer and the back electron transfer is also discussed.

Crystal-Structures of Three Long, Rigid, Norbornylogous Compounds of Relevance to Distance-Dependence Studies of Long-Range Intramolecular Electron-Transfer Processes

1987 ◽  
Vol 40 (12) ◽  
pp. 1951 ◽  
Author(s):  
DC Craig ◽  
MN Paddonrow
Keyword(s):  
Electron Transfer ◽  
Crystal Structures ◽  
Dipole Moments ◽  
Intramolecular Electron Transfer ◽  
Time Resolved ◽  
Transfer Processes ◽  
Distance Dependence ◽  
Molecular Backbone ◽  
Predicted Values ◽  
Electron Transfer Processes

Results of previous studies revealed that photoinduced intramolecular electron transfer between the dimethoxynaphthalene donor and dicyanomethylene acceptor groups in the series of rigid alicyclic compounds (2a)-(6a) is extremely rapid. As the first step towards determining the distance dependence of the rate of photoinduced intramolecular electron transfer in these molecules, crystal structures of (3a), (4b) and (5b), have been measured. The edge-to-edge distance between the two chromophores in (3a), (4b) and (5b) is 6.8, 9.4, and 11.5 � respectively. The estimated centre-to-centre separation between the chromophores in (2a)-(6a) ranges from c. 7.1 � in (2a) to c. 14.9 � in (6a). From these results, dipole moments of the charge-separated states of (2a)-(6a), following photoinduced intramolecular electron transfer, could be estimated. These predicted values were in excellent agreement with those determined experimentally by using the time-resolved microwave conductivity technique. An interesting structural feature of (3a), (4b) and (5b) is the pronounced curvature of the molecular backbone in these molecules. It is predicted that approximately 24 linearly fused norbornyl and bicyclo[2.2.0] units would complete a circle, forming a member of a novel class of macrocycles, tentatively called dogcollaranes.

Triplet porphyrins as donors in intramolecular electron transfer and their intermolecular interaction with free radicals

2001 ◽  
Vol 05 (01) ◽  
pp. 58-66 ◽  
Author(s):  
A. BLANK ◽  
T. GALILI ◽  
H. LEVANON
Keyword(s):  
Electron Transfer ◽  
Free Radicals ◽  
Short Review ◽  
Magnetic Interactions ◽  
Intramolecular Electron Transfer ◽  
Time Resolved ◽  
Different Types ◽  
Donor Acceptor ◽  
Light Energy Conversion ◽  
Related Compounds

Porphyrins and related compounds are basic moieties which upon photoexcitation produce paramagnetic transients important to many processes in biology, material science and light–energy conversion. This short review demonstrates the application of time-resolved EPR spectroscopy to two processes in which the photoexcited singlet and/or triplet are involved: (1) intramolecular electron transfer in photoexcited donor–acceptor systems embedded in liquid crystals, where the porphyrins are the electron donors attached to different types of acceptors; and (2) intermolecular magnetic interactions between photoexcited porphyrin triplets and free radicals. In both systems the electron spin plays an important part with regards to the route of the magnetic interactions involved.

Photoinduced electron transfer processes in three component rotaxanes with porphyrins, [60]fullerene and triphenylamine

2006 ◽  
Vol 10 (12) ◽  
pp. 1346-1359 ◽  
Author(s):  
Hisahiro Sasabe ◽  
Yoshio Furusho ◽  
Atula S.D. Sandanayaka ◽  
Yasuyuki Araki ◽  
Nobuhiro Kihara ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Charge Separation ◽  
Transient Absorption ◽  
Photophysical Properties ◽  
Solvent Polarity ◽  
Time Resolved ◽  
Transfer Processes ◽  
Back Electron Transfer ◽  
Electron Transfer Processes ◽  
Absorption Measurements

Electron transfer processes occurring through-space and through-bond were studied for novel mechanically linked triad [2]rotaxanes, which contain a porphyrin (MP) unit as a pendant and [60]fullerene ( C 60) and triphenylamine ( TPA ) moieties as stopper groups at the axle ends (abbreviated as ( MP ; C 60- TPA ) rot+ with MP = H 2 P or ZnP . The photophysical properties were investigated by means of time-resolved fluorescence and transient absorption measurements with changing solvent polarity. The charge separation took place mainly via(1 MP *; C 60- TPA ) rot+ and ( MP ;1 C 60*- TPA ) rot + in polar solvents. Within the charge-separated states of triads ( MP ; C 60- TPA ) rot +, hole-shift and/or back electron transfer took place competitively. The lifetime of the charge separation state of ( ZnP ; C 60- TPA ) rot+ was similar to that of dyad ( C 60- TPA ) rot+ (140 ns in dimethylformamide), whereas that of ( H 2 P ; C 60- TPA ) rot + was as long as 230 ns, suggesting two final charge separation states such as ( MP ; C 60•-- TPA •+) rot + and ( MP •+; C 60•-- TPA ) rot+ depending on the kind of porphyrin.

Through-bond modulation of intramolecular electron transfer in rigidly linked donor-acceptor systems

1989 ◽  
Vol 164 (2-3) ◽  
pp. 120-125 ◽  
Author(s):  
James M. Lawson ◽  
Donald C. Craig ◽  
Michael N. Paddon-Row ◽  
Jan Kroon ◽  
Jan W. Verhoeven
Keyword(s):  
Electron Transfer ◽  
Intramolecular Electron Transfer ◽  
Donor Acceptor
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