Synthesis and Characterization of Functionalized Polythiophene via Negishi Coupling

Abstract

Thiophene based conjugated polymers are a focal point for researchers across the globe because of their exceptional conductive properties and easy synthesis. The electronic properties of the conjugated backbone of polythiophenes can be tailored by the incorporation of different electron withdrawing and electron donating substituents. The present study aimed at synthesis and characterization of thiophene based polymers. In the first part of this study, a novel ester functionalized polythiophene (P1) was synthesized, starting from thiophene-3-carboxylic acid (1A), which undergoes bromination by reacting with NBS to form 2,5-dibromothiophene-3-carboxylic acid (2A), which then undergoes esterification reaction with BnOH to form ester (4A). In the second part an amide functionalized polythiophene (P2) was synthesized where octadecyl phenyl amine (1B) by reacting with 1A was converted into carboxamide (4B). The synthesized ester (4A) and amide (4B) were converted into organozinc reagent (5A and 5B) by Knochel reaction that finally undergoes Negishi mediated self polymerization reaction to form polymer (P1 and P2), in good yield of 48% and 52% respectively. The synthesized monomers and polymers were characterized by NMR and GC-MS spectroscopic techniques which confirmed the presence of all the functional groups in proposed structures and their purity. XRD analysis of polymers suggested their amorphous nature. Both type of derivitized polythiophenes were found to be highly soluble in common organic solvents, such as CHCl3, THF, MeOH and DMSO. The photophysical aspects of polymers were studied by UV-visible spectroscopy. The synthesized polymers exhibited broad and strong absorptions in the visible region ( λmax of P1 = 325nm and λmax of P2 = 310nm). Small Eg values (2.5eV-2.9eV) suggested that these polymers are potential candidates for opto-electronic properties and can be used in solar cell films and in thin film transistors etc