Theoretical design for organic nonlinear optical materials

We developed the Elongation-FF method incorporating Finite-field approach into the theoretical synthesis method of aperiodic polymers (Elongation method) for polymer NLO materials design. This method was applied to polydiacetylene (PDA) derivatives to examine the substituent effects. As the substituted systems, we adopted three models, that is, D-(-CH=CH-CEC-)_n-CH=CAH, (-CD=CA-CEC-CA=CD-)_n, (-CD=CD-CEC-CA=CA-)_n. As a result, it is shown that the last model exhibits much higher NLO properties than the other models. Furthermore, we examined the relationship between hydrogen bond interactions and second hyperpolarizability (β) to design molecular crystal NLO materials. Through-space/bond interaction analysis showed that the intermolecular hydrogen bond decreases β value of urea cluster.