Donor-acceptor polyenes, bond-length alternation

Meyers F, Marder SR, Pierce BM, Bredas JL (1994) Electric field modulated nonlinear optical properties of donor-acceptor polyenes sum-over-states investigation of the relationship between molecular polarizabilities (a, p, and y ) and bond length alternation. J Am Chem Soc 116 10703-10714... 

Bourhill, G., Bredas, J.L., Cheng, L.-T., Marder, S.R., Meyers, F., Perry, J.W., Tiemann, B.G. Experimental demonstration of the dependence of the first hyperpolarizability of donor-acceptor-substituted polyenes on the ground-state polarization and bond length alternation. J. Am. Chem. Soc. 116, 2619-2620(1994)... 

Luo et al. have investigated the influence of the solvent polarity on the NLO properties of a simple donor-acceptor polyene molecule (Scheme 4) at the ab initio level of theory applying the continuum model of solvent [107]. It has been shown that the evolution of the TPA cross section with respect to the bond length alternation (BLA) closely follows that of the static first-order hyperpolarizability, p. The TPA cross section is strongly dependent on the geometrical changes. Moreover, these authors have noticed that the solvent effect on the TPA cross section (for the CT excited state) in tlie typical donor-acceptor polyene molecule exhibiting the positive solvatochromism is smaller than the influence of the solvent on the values of p. 

F. Meyers, S. R. Marder, B. M. Pierce, and J. L. Bredas,/. Am. Chem. Soc., 116,10703 (1994). Electric Field Modulated Nonlinear Optical Properties of Donor-Acceptor Polyenes Sum-Over-States Investigations of the Relationship Between Molecular Polarizabilities (ot, and -y) and Bond Length Alternation. 

Studies by Meyers and co-workers have shown that the NLO response of many strong donor-acceptor molecules suffer from too much bond length alternation (on the order of 0.01 nm), which inhibits charge transfer in the excited state (132). jS is zero in the cyanine limit, however, when there is no bond length alternation. Interestingly, /S peaks with opposite sign when the BLA is either intermediate between the polyene/cyanine structure or intermediate between a cyanine/zwitterionic structure (BLA 0.004 nm) (133). One important result... 

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