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7 February 2008 Two-photon absorption in cross-shaped chromophores with phenylene-vinylene backbones
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While early investigations in two-photon absorption (TPA) mainly focused on developing structure/property relationships for organic molecules with a conjugated path extending in one dimension, more recent research efforts have also included molecules containing multiple TPA-active units or with multi-dimensional conjugated backbones. However, a complete understanding of how the number and structure of branches in chromophores affect TPA properties has not yet emerged. Here, we describe chromophores consisting of four donor-substituted branches linked to an aromatic core (benzene or pyrazine) and compare them with linear analogues with only two branches (donor-Π-donor distryrylbenzenes). It is shown that this design does not lead to large enhancement of the TPA cross sections, with only a modest increase being observed going from compounds with two to compounds with four branches. It is also shown that a molecular exciton model can describe semi-quantitatively both the one-photon and the two-photon spectra of this type of multi-branched compounds. In contrast to the one-photon case, the model shows that pure additivity of the TPA cross section should not, in general, be expected when two monomer units are coupled, and that the TPA cross section of the composite molecule depends on the relative orientation of the constituent units and on the strength and sign of the coupling interaction.
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Mariacristina Rumi, Stephanie J. K. Pond, Qing Zhang, Maximilienne Bishop, Yadong Zhang, Stephen Barlow, Seth R. Marder, and Joseph W. Perry "Two-photon absorption in cross-shaped chromophores with phenylene-vinylene backbones", Proc. SPIE 6891, Organic Photonic Materials and Devices X, 689104 (7 February 2008);

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