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 chi((2))(xxz), chi((2))(zxx), and chi((2))(zzz) coefficients of second order susceptibility at 1064 nm have been measured for both isomeric forms of substituted diarylethene in polymer films. The relationship between chi((2))(xxz), chi((2))(zxx), and chi((2))(zzz) 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 beta(xxz), beta(zxx), and beta(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 beta(z) value measured by the EFISH technique with respect to that calculated from the three components beta(xxz), beta(zxx), and beta(zzz).