Synthesis and characterization of novel polythiophenes bearing oligo(ethylene glycol) spacers and crown ethers

Two novel thiophene containing monomers (TM): 3-methyltetra(oxyethylene)oxy-4-methylthiophene (TM1) and 3-(((2-aminobenzo-18-crown-6-ethyl)triethoxy)oxy)-4-methylthiophene (TM2) were synthesized and characterized. Both monomers were polymerized in the presence of FeCl3 to give the corresponding copolymer (CPT1). TM2 was also copolymerized in the presence of 3-dodecylthiophene to lead a second copolymer (CPT2). On the other hand, TM1 and TM2 were homopolymerized under the same reaction conditions to give poly[3-methyltetra(oxyethylene)oxy-4-methylthiophene] (PT1) and poly[3-(((2-aminobenzo-18-crown-6-ethyl)triethoxy)oxy)-4-methylthiophene] (PT2), where the former was used as reference compound. Solvatochromic and thermochromic behaviors of these polymers were investigated. All polymers exhibited solvatochromism; in a mixture of chloroform–methanol 20:80, CPT1 gives a violet solution and its polymer backbone adopts a planar conformation. By contrast, in chloroform CPT1 adopts a twisted conformation, giving an orange solution. This copolymer exhibits also an extended conjugation length in the solid state at room temperature (dark red) and a less conjugated conformation after heating (yellow). CPT2 shows a similar thermochromic behavior as CPT1 in chloroform, but in the solid state its color changes from dark red to orange.