Second-Harmonic Generation Studies on Thermoreversible Helix–Helix Transition between Right-Handed $\alpha_{\text{R}}$- and Left-Handed $\omega_{\text{L}}$-Helices in Solid Film of Poly($\beta$-phenylpropyl l-aspartate)

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We prepared an electrically poled film of poly($\beta$-phenylpropyl l-aspartate) and performed second-harmonic generation (SHG) measurements to detect its thermo-reversible helix–helix transition between right-handed $\alpha_{\text{R}}$- and left-handed $\omega_{\text{L}}$-helices. In this poled film, the helical molecules are highly oriented and SHG intensity profiles were measured with various angular combinations of polarizer and analyzer. The in-plane anisotropies of SHG were interpreted by the polar C6 symmetry through the temperature region from 25 to 160°C, and then clearly reflected the thermo reversible transformation between the $\alpha_{\text{R}}$-helix and $\omega_{\text{L}}$-helix at 155°C on heating and at 142°C on cooling. The $\beta_{lmn}$ ratios of molecules evaluated from the $\chi$ components were found to be characteristic for each helical conformation; $\beta_{XZX,\alpha}:\beta_{ZXX,\alpha}:\beta_{ZZZ,\alpha}=8.7:2.0:1.0$ for the $\alpha_{\text{R}}$-helix (at 145°C) and $\beta_{XZX,\omega}:\beta_{ZXX,\omega}:\beta_{ZZZ,\omega}=5.3:3.3:0.7$ for the $\omega_{\text{L}}$-helix (at 160°C).
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2005-12-15