Photoswitching of the Second Harmonic Generation from Poled Phenyl-Substituted Dithienylethene Thin Films and EFISH Measurements

The photoswitching of the second harmonic generation signal of poled phenyl-substituted dithienylethene/polystyrene thin films evidence a different behavior in function by their molecular structure. The three nonzero χ XXZ (2), χ ZXX (2), and χ ZZZ (2) coefficients of second order susceptibility at 1064 nm have been measured for both isomeric forms of substituted diarylethene in polymer films. The relationship between χ XXZ (2), χ ZXX (2), and χ ZZZ (2) for symmetrical diarylethene (OMe–OMe and CN–CN) differs from that found for the asymmetrical OMe–CN chromophore, suggesting for the two symmetrically substituted molecules a two-dimensional first hyperpolarizability. The two-dimensional first hyperpolarizability model has been checked by a statistical analysis from the correlation between susceptibility and first hyperpolarizability. Analysis of β xxz, β zxx, and β zzz values confirm for OMe–OMe and CN–CN a two-dimensional charge flow pattern, which is different from the monodimensional OMe–CN. Moreover, the goodness of the our statistical model was confirmed by comparing the β z value measured by the EFISH technique with respect to that calculated from the three components β xxz, β zxx, and β zzz .