Department of Chemical Engineering, Laboratory for Advanced Materials, Tsinghua University, Beijing, PR China, 100084.
Langmuir. 2010 May 4;26(9):6755-61. doi: 10.1021/la9041056.
In this work, formation of photoinduced self-structured surface pattern and its correlation with chromophoric structures were studied by using a series of star-shaped azo compounds, which exist as stable molecular glass at room temperature. For the synthesis, a star-shaped precursor (Tr-AN) was prepared by a ring-open reaction between 1, 3, 5-triglycidyl isocyanurate and N-methylaniline. The star-shaped azo compounds were then synthesized through azo-coupling reactions between the precursor and diazonium salts of 4-nitroaniline, 2-methyl-4-nitroaniline, and 4-aminobenzonitrile, respectively. Through these steps, three azo compounds were obtained to bear different donor-acceptor type azo chromophores at the peripheral positions. The formation of the photoinduced self-structured patterns was investigated by irradiating solid thin films of the molecular azo glass with a uniform laser beam (532 nm, 200 mW/cm(2)) at normal incidence. For comparison, formation of surface-relief-gratings (SRGs) was also investigated by exposing the thin films to an interference pattern of the laser beams (532 nm, 80 mW/cm(2)). The results show that SRGs can be inscribed on the films of all three star-shaped azo compounds, but self-structured surface patterns is only observed on film of the azo compound containing 4-cyanoazobenzene moieties (Tr-AZ-CN) under the same irradiation condition. The electron-withdrawing groups, which control the absorption band position, show a significant influence on both the self-structured pattern formation and SRG inscription rate. Under proper experimental conditions, both self-structured surface pattern and SRG can simultaneously be observed on the Tr-AZ-CN films. The observations can lead to a deeper understanding of the photoinduced effects, especially their correlation with molecular structures.
在这项工作中，通过使用一系列星形偶氮化合物研究了光诱导自结构化表面图案的形成及其与发色团结构的关系，这些化合物在室温下以稳定的分子玻璃形式存在。为了合成，通过 1,3,5-三缩水甘油异氰尿酸酯与 N-甲基苯胺之间的开环反应制备了星形前体（Tr-AN）。然后通过前体与重氮盐之间的偶联反应分别合成了星形偶氮化合物，重氮盐分别为对硝基苯胺、2-甲基-4-硝基苯胺和 4-氨基苯甲腈。通过这些步骤，获得了三个带有不同给体-受体型偶氮发色团的偶氮化合物，分别位于外围位置。通过用均匀激光束（532nm，200mW/cm(2)）以垂直入射方式辐照分子偶氮玻璃的固体薄膜，研究了光诱导自结构化图案的形成。为了比较，还通过暴露于激光束（532nm，80mW/cm(2)）的干涉图案来研究表面浮雕光栅（SRG）的形成。结果表明，SRG 可以在所有三种星形偶氮化合物的薄膜上形成，但仅在含有 4-氰基偶氮苯部分的偶氮化合物（Tr-AZ-CN）的薄膜上观察到自结构化表面图案在相同的辐照条件下。控制吸收带位置的吸电子基团对自结构化图案形成和 SRG 刻写速率都有显著影响。在适当的实验条件下，可以同时在 Tr-AZ-CN 薄膜上观察到自结构化表面图案和 SRG。这些观察结果可以加深对光诱导效应的理解，特别是它们与分子结构的关系。
