Forster’s model

Within this framework, the solvent screening factor in Forster s model can be obtained as ratio between the total coupling and the direct coupling s = Ftot/ Vs. 

One of the most popular applications of molecular rotors is the quantitative determination of solvent viscosity (for some examples, see references [18, 23-27] and Sect. 5). Viscosity refers to a bulk property, but molecular rotors change their behavior under the influence of the solvent on the molecular scale. Most commonly, the diffusivity of a fluorophore is related to bulk viscosity through the Debye-Stokes-Einstein relationship where the diffusion constant D is inversely proportional to bulk viscosity rj. Established techniques such as fluorescent recovery after photobleaching (FRAP) and fluorescence anisotropy build on the diffusivity of a fluorophore. However, the relationship between diffusivity on a molecular scale and bulk viscosity is always an approximation, because it does not consider molecular-scale effects such as size differences between fluorophore and solvent, electrostatic interactions, hydrogen bond formation, or a possible anisotropy of the environment. Nonetheless, approaches exist to resolve this conflict between bulk viscosity and apparent microviscosity at the molecular scale. Forster and Hoffmann examined some triphenylamine dyes with TICT characteristics. These dyes are characterized by radiationless relaxation from the TICT state. Forster and Hoffmann found a power-law relationship between quantum yield and solvent viscosity both analytically and experimentally [28]. For a quantitative derivation of the power-law relationship, Forster and Hoffmann define the solvent s microfriction k by applying the Debye-Stokes-Einstein diffusion model (2)... 

Rosier, S.M., Shine, K.P., Forster, P.M.deF., and Tourpali, K. (1999) The impact of two decades of ozone change on the lower stratosphere, as simulated by the University of Reading Intermediate General Circulation Model (IGCM). In preparation. 

The asymptotic value of s, so = 0.54, falls in between the predictions of Forster model, sa = 1/n2 = 0.5, which assumes infinitely thin point dipoles, and the Onsager value, sa = 3/( hr1 + 1) = 0.6, which considers point dipoles contained in spherical cavities. It is reasonable to think that real molecules fall in between these two limits. The solvent screening factors obtained for the data set, along with the fitted screening function, Eq. 14, and the Forster and Onsager values are plotted in Fig. 8. 

Fig. 2.3 Solvent screening of electronic couplings between chromophores in the four photo-syntletic proteins PE545 (pink triangles), PC645 (blue inverted triangles), PSII/LHCII (green circles). The protein medium is modeled as a dielectric continuum medium with a relative static constant of estat = 15 and optical dielectric constant of n2 = 2. Calculated values for the solvent screening factor s for the various chromophores pairs. The Forster value I jnl and the Onsager value 3(2n1 + 1) are indicated by the horizontal line...

Figure 5.6 Cyclic voltammograms obtained for a spontaneously adsorbed [Os(bpy)2 4-tet Cl]+ monolayer on a 5 pm radius gold microdisk electrode where the scan rate is 1333 V s 1. The theoretical fits to the data, using a non-adiabatic electron tunneling model at electrolyte pH values of 0.9 and 6.0, are denoted by O and , respectively. In both cases, k is 27 kj mol-1, while k° is 1.1 x 103 and 1.1 x 104 s 1 at pH values of 0.9 and 6.0, respectively. Reprinted with permission from D. A. Walsh, T. E. Keyes, C. F. Hogan and R. J. Forster, ]. Phys. Chem., 105, 2792 (2000). Copyright (2000) American Chemical Society...

Figure 5.10 Cyclic voltammograms for a spontaneously adsorbed [Os(bpy)2(bpe)Cl]+ monolayer on a 25 pm radius platinum microdisk electrode at a scan rate of 6000 V s-1. The continuous line represents experimental data, while O and denote the best-fit theoretical responses generated by using the Finklea and Chidsey models, respectively. Both theoretical responses correspond to a k° of 9.4 x 103 s 1 and a AC 1 of 11.4 kj mol-1 the supporting electrolyte is aqueous 0.1 M UCIO4. Reprinted with permission from R. J. Forster, P. J. Loughman, E. Figgemeier, A. C. Lees, J. Hjelm and J. G. Vos, Langmuir, 16, 7871 (2000). Copyright (2000) American Chemical Society...

Coulson and Moffitf established a bent bond model of 1 by elaborating ideas first proposed by Forster ". They determined sp" (CC) and sp (CH) hybrid orbitals with optimal hybridization ratios n and m to describe bonding in 1. Calculations showed that, for 1, the p-character of the CC hybrid orbitals has to be increased from sp to sp" while the s-... 

Santacruz K, Lewis J, Spires T, Paulson J, Kotilinek L, Ingelsson M, Guimaraes A, DeTure M, Ramsden M, McGowan E, Forster C, Yue M, Ome J, Janus C, Maiiash A, Kuskowski M, Hyman B, Hutton M, Ashe KH (2005) Tau suppression in a neurodegenerative mouse model improves memory function. Science 309 476-481 Sayre LM, Perry G, Harris PL, Liu Y, Schubert KA, Smith MA (2000) In situ oxidative catalysis by neurofibrillary tangles and senile plaques in Alzheimer s disease a centrtil role for boimd transition metals. J Neurochem 74 270-279... 

K. Krause, E. Geidel, J. Kindler, H. Forster, and K. S. Smirnov, Vib. Spectrosc., 12,45 (1996). A Comparative Computer Modeling Study of Spectral Characteristics of Cation Exchanged Zeolite Y. 

Rieger P. T., Palese S. P. and Miller R. J. D. (1997), On the Forster model computational and ultrafast studies of electronic energy transport , Chem. Phys. 221, 85-102. 

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