19 September 2011 Modeling the hyperpolarizability dispersion with the Thomas-Kuhn sum rules
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The continued interest in molecules that possess large quadratic nonlinear optical (NLO) properties has motivated considerable interplay between molecular synthesis and theory. The screening of viable candidates for NLO applications has been a tedious work, much helped by the advent of the hyper-Rayleigh scattering (HRS) technique. The downside of this technique is the low efficiency, which usually means that measurements have to be performed at wavelengths that are close to the molecular resonances, in the visible area. This means generally that one has to extrapolate the results from HRS characterization to the longer wavelengths that are useful for applications. Such extrapolation is far from trivial and the classic 2-level model can only be used for the most straightforward single charge-transfer chromophores. An alternative is the TKSSOS technique, which uses a few input-hyperpolarizabilities and UV-Vis absorption data to calculate the entire hyperpolarizability spectrum. We have applied this TKS-SOS technique on a set of porphyrines to calculate the hyperpolarizability dispersion. We have also built a tunable HRS set up, capable of determining hyperpolarizabilities in the near infrared (up to 1600 nm). This has allowed us to directly confirm the results predicted in the application region. Due to the very sharp transitions in the hyperpolarizability dispersion, the calculation is subjected to a very precise calibration with respect to the input-hyperpolarizabilities, resulting in very accurate predictions for long wavelength hyperpolarizabilities. Our results not only underscribe the aforementioned technique, but also confirm the use of porphyrines as powerful moieties in NLO applications.
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Kurt De Mey, Kurt De Mey, Javier Perez-Moreno, Javier Perez-Moreno, Koen Clays, Koen Clays, } "Modeling the hyperpolarizability dispersion with the Thomas-Kuhn sum rules", Proc. SPIE 8113, Linear and Nonlinear Optics of Organic Materials XI, 81130V (19 September 2011); doi: 10.1117/12.893482; https://doi.org/10.1117/12.893482

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