Andreu, Raquel Carrasquer, Laura Franco, Santiago Garín, Javier Orduna, Jesús Martínez de Baroja, Natalia Alicante, Raquel Villacampa, Belén Allain, Magali 4<i>H</i>-Pyran-4-ylidenes: Strong Proaromatic Donors for Organic Nonlinear Optical Chromophores Merocyanines where a polyenic spacer separates a 4<i>H</i>-pyran-4-ylidene moiety and different strong organic acceptors have been synthesized. According to NMR studies and X-ray diffraction data, these compounds have weakly alternated structures and remarkably zwitterionic ground states, with a partial aromatic character that is compared to those of other pyran derivatives. The proaromaticity of the 4<i>H</i>-pyran-4-ylidene donor lies behind the cyanine-like behavior and low (positive or negative) second-order optical nonlinearities of the shorter derivatives. On the other hand, lengthening the π-spacer gives rise to rapidly increasing μβ<sub>1907</sub> values up to 17,400 × 10<sup>−48</sup> esu. nonlinearitie;polyenic spacer;moiety;zwitterionic ground states;NMR studies;Proaromatic Donors;esu;donor;compound;μβ1907 values;pyran derivatives;data;acceptor;proaromaticity;diffraction;Organic Nonlinear Optical ChromophoresMerocyanines 2009-09-04
    https://acs.figshare.com/articles/journal_contribution/4_i_H_i_Pyran_4_ylidenes_Strong_Proaromatic_Donors_for_Organic_Nonlinear_Optical_Chromophores/2830243
10.1021/jo901142f.s001