Híbridos moleculares de politiofenos e nanotubos de carbono para aplicação em dispositivos eletrocrômicos: preparação e caracterização

Abstract

This work reports the preparation of hybrid materials based on the intercalation between electron-acceptor (A) and electron-donor (D) subunits, beyond their characterization, especially the electrochromism. Firstly, the oxidized multi-walled carbon nanotubes (MWCNT-ox, A) were obtained by acid treatment of MWCNT and two aromatic amines (D) were synthesized: 3-amino-9-methylcarbazole (CbzNH2) and 3-amino-9-methyl-6-nitrocarbazole (NH2CbzNO2). Then, these amines were attached to the MWCNT-ox, yielding the A-D-like binary hybrids: MWCNTCO-NHCbz (1) and MWCNTCO-NHCbzNO2 (2). The precursor (1) was submitted to a chemical polymerization of 3-dodecylthiophene, yielding the first hybrid material (HIB-1). The precursor 2 was submitted to a reduction process in order to obtain the MWCNTCO-NHCbzNH2 precursor, in which was treated with 3-thiophenecarboxylic acid (ThCOOH, A), yielding the A-D-A ternary hybrid: MWCNTCO-NHCbzNH-COTh (HIB-2). Moving forward, poly(3-dodecylthiophene) and poly(3-hexylthiophene) were attached to this ternary precursor through the grafting technique, yielding two A-D-A-D-like quaternary hybrid materials: HIB-3 and HIB-4, respectively. After each functionalization step, the products were analyzed by spectroscopic techniques that corroborate the covalent bonds formation between the subunits and therefore, the formation of the expected hybrid materials. Through the thermogravimetric analysis of the hybrids, it was possible to estimate the MWCNT amount in each material, being ~45 wt% for both HIB-1 and HIB-3 and ~8 wt% for HIB-4. Clearly, it was observed the influence from the MWCNT over the optical, electrical and electrochemical properties of the hybrids – directly related to the MWCNT amount. Through the spectroelectrochemical characterization, these hybrids showed greater electrochromic performance compared to the homopolymers, particularly the HIB-3, that showed higher values of optical contrast and coloration efficiency, fast switching times and electrochromic cyclability. Therefore, this hybrid was chosen to build an electrochromic device that showed a reversible color changing process, switching from reddish orange to transmissive, even after 100 cycles. Generally, the enhancement of the properties observed for these hybrids, e.g. their lower bandgap energy, is directly related to their molecular architecture: A and D subunits covalently bonded.