Silva Lidiana M, Silva Daniel L, Boas Mariana V, Bretonniere Yann, Andraud Chantal, Vivas Marcelo G
Laboratório de Espectroscopia Óptica e Fotônica, Universidade Federal de Alfenas Poços de Caldas MG Brazil
Departamento de Ciências da Natureza, Matemática e Educação, Universidade Federal de São Carlos Rod. Anhanguera - Km 174 13600-970 Araras SP Brazil.
RSC Adv. 2020 Nov 9;10(67):40806-40814. doi: 10.1039/d0ra08379h.
Optical birefringence in polymeric films containing azo-chromophores is an important feature related to the development of several technologies such as electro-optic modulators, optical switching, and optical gates, to cite a few. Therefore, it is essential to understand the main underlying mechanisms describing dynamic switching. In this context, we have investigated the optical birefringence performance of a guest-host film produced from a poly(methyl methacrylate) (PMMA) matrix containing a V-shaped azo-chromophore, which exhibited a larger optical response in comparison to the linear chromophores. The optical birefringence was induced by a linearly polarized diode laser (532 nm, writing laser), while a low-intensity HeNe (632.8 nm) laser and a tungsten-halogen lamp are employed, respectively, to monitor the optical storage and the absorption change during the photoinduced birefringence. Our results pointed out that the guest-host film presents maximum residual optical memory at around 50% and local optical birefringence at around 3.3 × 10 in the low concentration and intensity regimes. The high optical birefringence obtained in guest-host films was attributed to the considerable photoisomerization quantum yield in the solid-state (0.15 ± 0.02 for 532 nm). Besides, we have shown that the switching mechanism is driven by angular hole-burning during the first seconds after excitation, and, subsequently, molecular reorientation quickly rises, dominating the photochemical process. The latter mechanism is highly efficient in converting to molecules (100%), which is responsible for the high residual optical memory obtained. In order to better understand the isomerization mechanism of the azo-chromophore/PMMA film, we performed quantum chemical calculations within the DFT framework. The electronic transitions of the azo-chromophore isomers were determined using the TD-DFT method and potential energy curves (PECs) were constructed to investigate the possibility of the thermal-isomerization process of the V-shaped azo-chromophore through both rotation and inversion mechanisms. For both mechanisms, the amplitude of the energy barrier and activation energy for thermal isomerization are determined and the results are discussed.
含偶氮发色团的聚合物薄膜中的光学双折射是与多种技术（如电光调制器、光开关和光闸等）发展相关的一个重要特性。因此，了解描述动态开关的主要潜在机制至关重要。在此背景下，我们研究了由含V形偶氮发色团的聚甲基丙烯酸甲酯（PMMA）基质制成的客体 - 主体薄膜的光学双折射性能，该薄膜与线性发色团相比表现出更大的光学响应。光学双折射由线偏振二极管激光器（532 nm，写入激光器）诱导，同时分别使用低强度氦氖（632.8 nm）激光器和钨卤灯来监测光致双折射过程中的光存储和吸收变化。我们的结果指出，在低浓度和低强度条件下，客体 - 主体薄膜在约50%时呈现最大残余光学记忆，局部光学双折射约为3.3×10 。客体 - 主体薄膜中获得的高光双折射归因于固态下可观的光异构化量子产率（532 nm时为0.15±0.02）。此外，我们表明，开关机制在激发后的最初几秒内由角烧孔驱动，随后分子重新取向迅速上升，主导光化学过程。后一种机制在将 转化为 分子方面非常高效（100%），这是获得高残余光学记忆的原因。为了更好地理解偶氮发色团/PMMA薄膜的异构化机制，我们在DFT框架内进行了量子化学计算。使用TD - DFT方法确定偶氮发色团异构体的电子跃迁，并构建势能曲线（PEC）以研究V形偶氮发色团通过旋转和反转机制进行热异构化过程的可能性。对于这两种机制，都确定了热异构化的能垒幅度和活化能，并对结果进行了讨论。
