Ultrafast electron transfer

Wynne K and Hochstrasser R M 1999 Coherence and adiabaticity in ultrafast electron transfer Adv. Chem. Phys. 107 (Electron transfer from isolated molecules to biomolecules) part 2, 263-309... 

The ultrafast photoreactions in PNS of these proteins take place immediately after conversion from the FC state to vibrationally unrelaxed or only partially relaxed FI state [1-3]. For PYP [1] and Rh [3], the primary process is twisting of the chromophore, which causes the ultrafast fluorescence quenching, in the course of the isomerization, while the primary process for FP [2] is the ultrafast electron transfer leading to the fluorescence quenching reaction in PNS. Thus, in spite of the different molecular structures of PYP, Rh and FP chromophores and different kind of photoinduced reactions, these photoresponsive proteins show ultrafast and highly efficient photoreactions from FI state of similar nature (vibrationally unrelaxed or only partially relaxed), suggesting the supremely important role of the PNS controlling the reactions. 

The above CT systems represent the case for intermolecular electron transfer. There is some analogy to proton transfer in acid-base reactions [5]. We have also examined intramolecular electron transfer systems and studied the influence of IVR and geometric changes this work is detailed elsewhere [5]. Other reactions involving ultrafast electron transfer are those of harpooning in Xe + I2) Nal, and more recently Xe/Ch (see Ref. 1). 

A microscopic theory for describing ultrafast radiationless transitions in particular for, photo-induced ultrafast radiationless transitions is presented. For this purpose, one example system that well represents the ultrafast radiationless transaction problem is considered. More specifically, bacterial photosynthetic reaction centers (RCs) are investigated for their ultrafast electronic-excitation energy transfer (EET) processes and ultrafast electron transfer (ET) processes. Several applications of the density matrix method are presented for emphasizing that the density matrix method can not only treat the dynamics due to the radiationless transitions but also deal with the population and coherence dynamics. Several rate constants of the radiationless transitions and the analytic estimation methods of those rate... 

To observe ultrafast electron transfer taking place in photosynthetic reaction centers, what are the possible experimental techniques ... 

Experiments carried out on various blends with MDMO-PPV PCBM weight ratios ranging from 1 3 to 1 0.5 all displayed the same ultrafast electron transfer process, with a dynamics which was found to be almost independent of concentration. For much lower PCBM concentrations (weight ratios lower than 1 0.05), the formation time of the PA band increases to a few ps and the formation rate becomes a linear function of PCBM concentration. This indicates that, as previously observed [94], at low acceptor concentrations we enter a new regime in which the charge transfer process is mediated by disorder-induced diffusion of the excitations, which migrate until they reach a site favourable for charge transfer. 

STUDIES OF ULTRAFAST ELECTRON TRANSFER IN A LIGHT-ACTIVATED PROTEIN... 

Van Brederode, M. E., and Van Grondelle, R., 1999, New and unexpected routes for ultrafast electron transfer in photosyndietic reaction centers. FEES Letts., 455 ln7. 

Zinth W, Wachtveitl J. The first picoseconds in bacterial photosynthesis - Ultrafast electron transfer for the efficient conversion of light energy. ChemPhysChem. 2005 6 871-880. 

Polypyridine complexes of Fe(II) are strongly colored due to MLCT transitions. However, their MLCT excited states are very short-lived because of an efficient deactivation through lower-lying LF states. MLCT excited state lifetimes of [Fe(N,N)3] + range from 2.54 ns for tpy to 0.8 ns for bpy and phen [270]. Therefore, Fe complexes were deemed unsuitable for electron-transfer reactions. Recently, there is a renewed interest in excited state properties of Fe -polypyridines caused by the observation [304] of an ultrafast electron transfer from [Fe(4,4 -(COOH)2-bpy)2(CN)2] (tq = 330 ps) to Ti02, see Section 5.4.6. 

Femtosecond TRIR spectroscopy was used to probe vibrational mode coupling to ultrafast electron transfer in [(NC)50sCNRu(NH3)5]. 275 The IR spectrum of (ri2-C6o)Os(CO)(tBuNC)(PPh3)2 includes vCN at 2153 cm 1, with vCO at 1953 cm-1.276... 

Infrared Spectroelectrochemical Investigations of Ultrafast Electron Transfer in Mixed-Valence Complexes... 

Anderson N. A. and Lian T. Q. (2005), Ultrafast electron transfer at the molecule-semiconductor nanoparticle interface , Annu. Rev. Phys. Chem. 56, 491-519. 

Ai X., Anderson N. A., Asbury J. B., Hao E. and Lian T. (2003), Ultrafast electron transfer dynamics from molecular adsorbate to semiconductor nanoparticles , Proc. SPIE—The International Society for Optical Engineering 5223, 147-158. 

Asbury J. B., Hao E., Wang Y. and Lian T. (2000), Bridge length-dependent ultrafast electron transfer from Re polypyridyl complexes to nanocrystalline Ti02 thin films studied by femtosecond infrared spectroscopy , J. Phys. Chem. B 104, 11957-11964. 

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