de Miguel Gustavo, Martín-Romero María T, Pedrosa José M, Muñoz Eulogia, Pérez-Morales Marta, Richardson Tim H, Camacho Luis
Departamento de Química Física y Termodinámica Aplicada, Universidad de Córdoba, Campus Universitario de Rabanales, Ed. Marie Curie, E-14071 Córdoba, Spain.
Phys Chem Chem Phys. 2008 Mar 21;10(11):1569-76. doi: 10.1039/b717737b. Epub 2008 Jan 24.
In this paper, the different aggregation modes of a water-insoluble porphyrin (EHO) mixed with an amphiphilic calix[8]arene (C8A), at the air-water interface and in Langmuir-Blodgett (LB) film form, are analyzed as a function of the mixed composition. The strategy used to control the EHO aggregation has consisted of preparing mixed thin films containing EHO and C8A, in different ratios, at the air-water interface. Therefore, the increase of the C8A molar ratio in the mixed film diminishes the aggregation of the EHO molecules, although such an effect must be exclusively related to the dilution of the porphyrin. The reflection spectra of the mixed C8A-EHO films registered at the air-water interface, show a complex Soret band exhibiting splitting, hypochromicity and broadening features. Also, during the transfer process at high surface pressure, it has been shown that the EHO molecules are ejected from the C8A monolayer and only a fraction of porphyrin is transferred to the solid support, in spite of a complete transfer for the C8A matrix. The complex structure of the reflection spectra at the air-water interface, as well as the polarization dependence of the absorption spectra for the mixed LB films, indicate the existence of four different arrangements for the EHO hosted in the C8A matrix. The aggregate formation is governed by two factors: the attraction between the porphyrin rings which minimizes their separation, and the alkyl chain interactions, that is, hydrophobic effect and/or steric hindrance which determine and restrict the possible aggregation structures. By using the extended dipole model, the assignment of the spectral peaks observed to different EHO aggregates is shown.
在本文中，分析了一种水不溶性卟啉（EHO）与两亲性杯[8]芳烃（C8A）在空气 - 水界面以及以朗缪尔 - 布洛杰特（LB）膜形式存在时的不同聚集模式，作为混合组成的函数。用于控制EHO聚集的策略包括在空气 - 水界面制备含有不同比例EHO和C8A的混合薄膜。因此，混合膜中C8A摩尔比的增加会减少EHO分子的聚集，尽管这种效应一定仅仅与卟啉的稀释有关。在空气 - 水界面记录的C8A - EHO混合膜的反射光谱显示出一个复杂的Soret带，呈现出分裂、减色和展宽特征。此外，在高表面压力下的转移过程中，已表明EHO分子从C8A单分子层中被挤出，并且尽管C8A基质能完全转移，但只有一部分卟啉被转移到固体支撑物上。空气 - 水界面反射光谱的复杂结构以及混合LB膜吸收光谱的偏振依赖性表明，在C8A基质中存在四种不同的EHO排列方式。聚集体的形成受两个因素控制：卟啉环之间的吸引力，它使它们的间距最小化；以及烷基链相互作用，即疏水效应和/或空间位阻，它们决定并限制了可能的聚集结构。通过使用扩展偶极子模型，展示了将观察到的光谱峰归属于不同EHO聚集体的情况。
