Ando Rômulo A, do Nascimento Gustavo M, Landers Richard, Santos Paulo S
Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, CEP 05513-970, CP 26077 São Paulo, SP, Brazil.
Spectrochim Acta A Mol Biomol Spectrosc. 2008 Feb;69(2):319-26. doi: 10.1016/j.saa.2007.03.046. Epub 2007 Apr 8.
For the first time, the resonance Raman spectroscopy was used to characterize polymers derived from meta- and para-nitroanilines. In order to improve the polymer structure analysis, other techniques were also used such as FTIR, UV-vis, XRD, XPS, EPR and N K-XANES. The insertion of strong electron-withdrawing groups (NO2) in polyaniline (PANI)-like backbone causes drastic changes in the lower energy charge transfer states, related to the polymer effective conjugation length. The resonance Raman data show that the NO2 moiety has a minor contribution on the CT state in poly(meta-nitroaniline), PMN, while in the poly(para-nitroaniline), PPN, the quinoid structure induced by para-substitution increases the charge density of NO2 groups, causing a more localized chromophore. The characterization of the imine nitrogen and of the protonated segments was done by XPS, N K-XANES and EPR spectroscopies and the lower polymerization degree of PPN, in comparison to PMN, is confirmed by XRD and TG data.
首次使用共振拉曼光谱对由间硝基苯胺和对硝基苯胺衍生的聚合物进行表征。为了改进聚合物结构分析，还使用了其他技术，如傅里叶变换红外光谱（FTIR）、紫外可见光谱（UV-vis）、X射线衍射（XRD）、X射线光电子能谱（XPS）、电子顺磁共振（EPR）和氮K边X射线吸收近边结构（N K-XANES）。在聚苯胺（PANI）类主链中引入强吸电子基团（NO2）会导致与聚合物有效共轭长度相关的低能量电荷转移态发生剧烈变化。共振拉曼数据表明，NO2部分对聚间硝基苯胺（PMN）的电荷转移态贡献较小，而在聚对硝基苯胺（PPN）中，对位取代诱导的醌型结构增加了NO2基团的电荷密度，导致发色团更加局域化。通过XPS、N K-XANES和EPR光谱对亚胺氮和质子化片段进行了表征，XRD和热重分析（TG）数据证实，与PMN相比，PPN的聚合度较低。
