Synthesis and Characterization of Novel Polythiophenes Containing Azobenzene Units and Well-Defined Oligo(Ethylene Glycol) Spacers: Thermal and Optical Properties, and Preparation of Langmuir Films

Abstract

A new series of 3-alkyl-ester-substituted polythiophenes, bearing amino-nitro substituted azobenzenes and flexible tetra(ethylene glycol) spacers, have been synthesized and characterized. First an amphiphilic monomer (E)-2-(4-((4-nitrophenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl 2-(tiophen-3-yl) acetate (AT) was prepared and homo-polymerized to give the corresponding polymer poly[(E)-2-(4((4-nitrophenyl)diazenyl)phenyl)-5,8,11-trioxa-2-azatridecan-13-yl 2-(tiophen-3-yl) acetate] (HP). This monomer was also co-polymerized in the presence of 3-butylthiophene, 3-hexylthiophene and 3-dodecylthiophene to give the corresponding co-polymers CP4, CP6 and CP12. These polymers exhibited molecular weights ranging between 16 500 and 46 990 g/mol. HP showed lower thermal stability than the corresponding co-polymers CP4, CP6 and CP12. The use of 3-alkylthiophene plastificant co-monomers conferred higher thermal stability to the obtained co-polymers. Polymers bearing higher azobenzene content showed to be more susceptible to degradation. All polymers exhibited a maximum absorption band at λ max = 456–475 nm, due to the amino-nitro-substituted azobenzene units. Finally, Langmuir films were prepared with HP and CP4, whose formation was monitored by plotting their surface pressure vs. molecular area (π/A) isotherms and by Brewster angle microscopy (BAM).