Characteristics of Low Band Gap Copolymers Containing Anthracene-Benzothiadiazole Dicarboxylic Imide: Synthesis, Optical, Electrochemical, Thermal and Structural Studies.

Ary R Murad,Shujahadeen B Aziz,Ahmed Iraqi,Sozan N Abdullah,Mohammed S Almeataq,Mohamad A Brza

doi:10.3390/polym13010062

Abstract

Two novel low band gap donor–acceptor (D–A) copolymers, poly[9,10-bis(4-(dodecyloxy)phenyl)-2,6-anthracene-alt-5,5-(4′,7′-bis(2-thienyl)-2′,1′,3′-benzothiadiazole-N-5,6-(3,7-dimethyloctyl)dicarboxylic imide)] (PPADTBTDI-DMO) and poly[9,10-bis(4-(dodecyloxy)phenyl)-2,6-anthracene-alt-5,5-(4′,7′-bis(2-thienyl)-2′,1′,3′-benzothiadiazole-5,6-N-octyl-dicarboxylic imide)] (PPADTBTDI-8) were synthesized in the present work by copolymerising the bis-boronate ester of 9,10-phenylsubstituted anthracene flanked by thienyl groups as electron–donor units with benzothiadiazole dicarboxylic imide (BTDI) as electron–acceptor units. Both polymers were synthesized in good yields via Suzuki polymerisation. Two different solubilizing alkyl chains were anchored to the BTDI units in order to investigate the impact upon their solubilities, molecular weights, optical and electrochemical properties, structural properties and thermal stability of the resulting polymers. Both polymers have comparable molecular weights and have a low optical band gap (Eg) of 1.66 eV. The polymers have low-lying highest occupied molecular orbital (HOMO) levels of about −5.5 eV as well as the similar lowest unoccupied molecular orbital (LUMO) energy levels of −3.56 eV. Thermogravimetric analyses (TGA) of PPADTBTDI-DMO and PPADTBTDI-8 did not prove instability with decomposition temperatures at 354 and 313 °C, respectively. Powder X-ray diffraction (XRD) studies have shown that both polymers have an amorphous nature in the solid state, which could be used as electrolytes in optoelectronic devices.

Highlights

Organic solar cells are a promising alternative to traditional inorganic semiconducting materials [1,2]
The results indicate that anchoring different chains (n-octyl vs. 3,7-dimethyloctyl) on the imide functionality of the benzothiadiazole dicarboxylic imide (BTDI) building blocks provides polymers with similar processability and has a negligible impact on the Mn values of the resulting polymers
Two low band gap alternating copolymers comprising of 2,6-linked anthracene moieties flanked by thienyl units as electron donor units and benzothiadiazole dicarboxylic imide (BTDI) as electron acceptor units were synthesised through Suzuki polymerisation, and yielded PPADTBTDI-DMO and PPADTBTDI-8

Summary

Introduction

Organic solar cells are a promising alternative to traditional inorganic semiconducting materials [1,2]. The flask cooled to RT and the solvent was removed to afford the product which was purified by column chromatography with gradient (petroleum ether, 0–50% DCM) to obtain material 6 as yellow crystals (2.37 g, 6 mmol, 94% yield). The organic phase dried over MgSO4 and the solvent was evaporated to obtain the product which was purified via chromatography with dichloromethane to yield material 10 as a colourless oil (5.29 g, 18 mmol, 91% yield). The mixture was cooled to RT and the solvent was concentrated to yield the product which was purified by chromatography with (60:10, petroleum ether: ethyl acetate) to afford material 12 as an orange solid (1.15 g, 2.3 mmol, 84% yield). The flask was cooled to RT, the polymer was dissolved in CHCl3 (200 mL) and an NH4OH solution (50 mL, 35% in H2O) was added and the mixture stirred overnight. Found: C, 72.97; H, 7.05; N, 3.38; S, 7.58

Molecular Weights and Yield

Optical Properties

Electrochemical Properties

Thermal Properties

Conclusions