Construction of Sn^IV Porphyrin/Trinuclear Ruthenium Cluster Dyads Linked by Pyridine Carboxylates: Photoinduced Electron Transfer in the Marcus Inverted Region

Abstract

Novel conglomerates consisting of saddle-distorted Sn(IV)(DPP) (H(2)DPP = dodecaphenylporphyrin) complexes and mu(3)-O-centered and carboxylato-bridged trinuclear Ru(III) clusters linked by pyridine carboxylates were synthesized and characterized. Sn(IV)-DPP complexes with Cl(-), OH(-), and 3- and 4-pyridine carboxylates ligands were characterized by spectroscopic methods and X-ray crystallography. Reactions of [Sn(DPP)(pyridinecarboxylato)(2)] with trinuclear Ru(III) clusters gave novel conglomerates in moderate yields. The conglomerates are stable in solution as demonstrated by (1)H NMR and electrospray ionization mass spectrometry (ESI-MS) measurements, which show consistent spectra with those expected from their structures, and also by electrochemical measurements, which exhibit reversible multistep redox processes. This stability stems from the saddle distortion of the DPP(2-) ligand to enhance the Lewis acidity of the Sn(IV) center that strengthens the axial coordination of the linker. The fast intramolecular photoinduced electron transfer from the Sn(IV)(DPP) unit to trinuclear Ru(III) clusters, affording the electron-transfer (ET) state {Sn(DPP(*+))-Ru(II)Ru(III)(2)}, was observed by femtosecond laser flash photolysis. The lifetimes of ET states of the conglomerates were determined to be in the range 98-446 ps, depending on the clusters and energies of the ET states. The reorganization energy of the electron transfer was determined to be 0.58+/-0.08 eV in light of the Marcus theory of electron transfer. The rate constants of both the photoinduced electron transfer and the back electron transfer in the conglomerates fall in the Marcus inverted region due to the small reorganization energy of electron transfer.

Cyanobuta‐1,3‐dienes as Novel Electron Acceptors for Photoactive Multicomponent Systems

“…The former is longer-lived and attributable to the porphyrin triplet, [65] whilst the latter is substantially shorter and is fitted through a single-exponential decay of 2.3 ms. This is a rather long lifetime for a charge-separated state and can be rationalized in terms of "Marcus inverted region" behavior, [78,81] because the driving force for charge recombination ÀDG CR is large (1.39 eV) and exceeds the total reorganization energy (l, 1.30 eV). [82] We notice that, in benzonitrile, the porphyrin fluorescence quantum yield (F FL ) and singlet lifetime ( 1 t) of 2 (1.0 %, 750 ps) are considerably quenched with respect to ZnP-0A (F FL = 2.9 % and 1 t = 1.80 ns), and the generation of the CS state can be predominantly attributed to the porphyrin singlet manifold.…”

Photoinduced Electron Transfer in 9‐Substituted 10‐Methylacridinium Ions

“…[1][2][3] Extensive efforts have been devoted to developing artificial systems mimicking the photosynthetic reaction center. [4][5][6][7][8][9][10][11] The best mimic of the multistep ET processes in the photosynthetic reaction center so far reported is af errocene-meso,meso-linked porphyrint rimer-fullerene pentad (Fc-(ZnP) 3 -C 60 )i nw hichC 60 and Fc are tethered at the two ends of (ZnP) 3 (R ee = 46.9 ). [12] The lifetime of the final CS state of 0.53 sat163 Kw as attained withoutlowering the CS efficiency (F = 0.83).…”

Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(iii) porphyrin and fullerene entities

“…8,11,16,[26][27][28][29][30] However, there are fewer studies of these factors in complexes with the components linked axially via the central element of the Por ring. [31][32][33][34][35][36][37][38][39][40][41][42][43] In the natural reaction centers the chlorophylls are generally bound to the protein via axially ligation, often by histidine, and the axial ligands are important for controlling factors such as the free energy change and electronic coupling that govern electron transfer. 44 For artificial complexes, an added advantage of the axial arrangement is that the placement of the donor and acceptor units on opposite faces of the porphyrin ensures that they are spatially well separated and that unwanted interactions are minimized.…”