Electron transfer across bridges

Indelli, M. T., Chiorboli, C., Flamigni, L., De Cola, L., Scandola, E, Photoinduced electron transfer across oligo-p-phenylene bridges. Distance and conformational effects in Ru0I) Rh0II) dyads. Inorg. Chem. 2007, 46, 5630-5641. 

The effects of concentration and sample purity on the redox potentials of the Fen/Fein couple in heme have also been studied usually the midpoint potentials are much higher in concentrated solutions than in more dilute ones [Adler (1)]. Reduction of FemCl36 TPP with Cr11 salts leads to a 96% percent transfer of the radioactivity towards the Crm product which confirms the inner-sphere electron transfer across an Fe—Cl—Cr-bridge [Cohen (37)]. 

Recendy, Sneddon and Brooks (39), on the basis of their CHARMM simulations of conformational dynamics of Pro peptides in aqueous solution, have postulated involvement in electron transfer across the -(Pro) -bridge of P — a transitions at the i i angle, as the latter occur more rapidly and bring the donor-acceptor distance to a shorter range than the trans cis interconversion... 

Such processes in bridged anthracenes were recently reported by Fiedler et al. (38), and the general question of electron transfer across spacers connecting aromatic molecules has received recent attention (39). 

Some examples of donor-acceptor dyads for studies of photoinduced electron transfer across molecular bridges are shown in Fig. These systems are usually... 

Fig. 2 Examples of covalently linked donor-acceptor systems (dyads) used for the study of photoinduced electron transfer across organic spacers. Boxes are drawn to identify the photoexcitable chromophore (left), the bridge (center), and the acceptor unit (right).

Fig. 3 Schematic representation of two limiting mechanisms for photoinduced electron transfer across a bridge superexchange (a) and...

Figure 13.13. Energetic positioning of photoexcited state D and accepter LUMO in electron transfer across saturated or conjugated covalent bridges.

Williams R M, Koeberg M, Lawson J M, An Y-Z, Rubin Y, Paddon-Row M N and Verhoeven J W 1996 Photoinduced electron transfer to Cgg across extended 3- and 11 a-bond hydrocarbon bridges creation of a long-lived charge-separated state J. Org. Chem. 61 5055-62... 

The Creutz-Taube anion, [(NH3)5Ru- N(CH=CH)2N Ru(NH3)5] + displays more obvious redox properties, yielding both 4+ and 6- - species, and much interest has focused on the extent to which the pyrazine bridge facilitates electron transfer. A variety of spectroscopic studies supports the view that low-energy electron tunnelling across the bridge delocalizes the charge, making the 5- - ion symmetrical. Other complexes, such as the anion [(CN)5Ru (/z-CN)Ru (CN)5] , are asymmetric... 

Chiorboli C, Indelli MT, Scandola F (2005) Photoinduced Electron/Energy Transfer Across Molecular Bridges in Binudear Metal Complexes. 257 63-102 Coleman AW, Perret F, Moussa A, Dupin M, Guo Y, Perron H (2007) Calix[n]arenes as Protein Sensors. 277 31-88... 

One of the advances in the field of PET is the design of molecular devices, in which D and A pairs are ingeniously linked by covalent bridges (B) to form D-B-A dyads. Electron transfers between D and A across B in a controlled manner may thus display useful functionalities, such as molecular rectifiers [25], switches [26], biosensors [27], photovoltaic cells [28], and nonlinear optical materials [29]. Spacers that have been utilized are versatile, including small molecules, such as cyclohexane [30], adamantane [31], bicyclo[2.2.2]octane [32], steroids [33], and oligomers of... 

R. M Williams, M Koebeig, J. M Lawson, Y. Z. An, Y. Rubin, M N. Paddon-Row, J. W. Verhoeven, Photoin-duced Electron Transfer to C-60 Across Extended 3-and 11-Bond Hydrocarbon Bridges - Creation of a Long-Lived Chaige-Separated State , J. Org. Chem 1996, 61,5055-5062... 

Chiorboli C, Indelli MT, Scandola F (2005) Photoinduced Electron/Energy Transfer Across Molecular Bridges in Binuclear Metal Complexes. 257 63-102 Collin J-P, Heitz V, Sauvage J-P (2005) Transition-Metal-Complexed Catenanes and Rotax-anes in Motion Towards Molecular Machines. 262 29-62 Collyer SD, see Davis F (2005) 255 97-124 Commeyras A, see Pascal R (2005) 259 69-122 Correia JDG, see Santos I (2005) 252 45-84 Costanzo G, see Saladino R (2005) 259 29-68 Credi A, see Balzani V (2005) 262 1-27 Crestini C, see Saladino R (2005) 259 29-68... 

Additional work by the Forster group, making use of transient emission spectroscopy, probed the rate of photoinduced electron transfer between metal centers within a novel trimeric complex [Os(II)(bpy)2(bpe)2 ] [Os(II) (bpy)2Cl]2 4+, where bpy is 2,2/-bipyridyl and bpe is fra s-l,2-bis-(4-pyridyl) ethylene. Transient emission experiments on the trimer, and on [Os(bpy)2(bpe)2]2+ in which the [Os(bpy)2Cl]+ quenching moieties are absent, reveal that the rate of photoinduced electron transfer (PET) across the bpe bridge is 1.3 0.1 x 108s-1. The electron transfer is believed to be from the peripheral Os(II)Cl metal centers to the [Os(bpy)2(bpe)2]2+ chro-mophore. Comparison to rate constants for reduction of monolayers at a Pt electrode reveals that the photoinduced process is significantly faster [39]. 

Chiorboli C, Indelli MT, Scandola F (2005) Photoinduced Electron/Energy Transfer Across Molecular Bridges in Binuclear Metal Complexes. 257 63-102... 

While such a device has yet to be constructed, Debreczeny and co-workers have synthesized and studied a linear D-A, -A2 triad suitable for implementation in such a device.11641 In this system, compound 6, a 4-aminonaphthalene monoimide (AN I) electron donor is excited selectively with 400 nm laser pulses. Electron transfer from the excited state of ANI to Ai, naphthalene-1,8 4,5-diimide (NI), occurs across a 2,5-dimethylphenyl bridge with x = 420 ps and a quantum yield of 0.95. The dynamics of charge separation and recombination in these systems have been well characterized.11651 Spontaneous charge shift to A2, pyromellitimide (PI), is thermodynamically uphill and does not occur. The mechanism for switching makes use of the large absorption cross-section of the NI- anion radical at 480 nm, (e = 28,300). A second laser pulse at 480 nm can selectively excite this chromophore and provide the necessary energy to move the electron from NI- to PI. These systems do not rely on electrochemical oxidation-reduction reactions at an electrode. Thus, switching occurs on a subpicosecond time scale. 

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