Department of Chemical Sciences, Indian Institute of Science Education and Research, Kolkata, Mohanpur 741246, West Bengal, India.
Department of Physical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, West Bengal, India.
Phys Chem Chem Phys. 2023 Feb 15;25(7):5849-5856. doi: 10.1039/d2cp05462k.
A series of chiral peptide luminophores containing the coumarin moiety was synthesized a simple and efficient solution-based procedure. The peptides, containing either L-Phe, or L-Ala, or L-Leu (designated, respectively, as p1, p2, and p3), self-aggregate to form anti-parallel sheet-like structures. The self-assembly of the peptide luminophores leads to non-centrosymmetric crystals which display significant second harmonic generation (SHG). The dependence of the SHG intensity on the input laser polarization revealed a strong correlation between the SHG and the crystal packing. In the polar plots, the SHG intensity as a function of the linear polarization orientation of the input laser beam gave a four-petal pattern for p1, a predominantly two-petal pattern for p2, and a dumbbell-shaped pattern for p3. This reflects the dependence of the second order optical susceptibility tensor on the crystal symmetry. The polar plots can be fitted very well with the theoretical expressions derived from the second order polarization equation after incorporating crystal symmetry in the second order optical susceptibility tensor. The strong polarization-dependent SHG from organic crystals may be interesting for polarization controlled nonlinear optical switches, sensors, and actuators.
一系列含有香豆素部分的手性肽类发光团通过简单高效的溶液法合成。这些肽包含 L-苯丙氨酸、L-丙氨酸或 L-亮氨酸（分别命名为 p1、p2 和 p3），自组装形成反平行片状结构。肽类发光团的自组装导致非中心对称晶体，表现出显著的二次谐波产生（SHG）。SHG 强度对输入激光偏振的依赖性表明 SHG 与晶体堆积之间存在很强的相关性。在极坐标图中，SHG 强度作为输入激光束线性偏振方向的函数，p1 给出了四瓣图案，p2 主要给出了两瓣图案，p3 给出了哑铃状图案。这反映了二阶光学有效张量对晶体对称性的依赖性。极坐标图可以通过在二阶光学有效张量中包含晶体对称性，用二阶极化方程推导出的理论表达式很好地拟合。有机晶体的强偏振相关 SHG 可能对偏振控制的非线性光学开关、传感器和执行器很有趣。
