All organic double cable polymers of a polythiophene donor with rhodanine and perylene diimide acceptors and evaluation of photocurrent generation

Abstract

Photoactive interfaces derived from all organic double cable polymers (O-DCPs) consisting of covalently conjugated photoelectron donor (D) and electron acceptor (A) molecular components are being recognized as promising light energy harvesting systems. Compared to the limitations faced by the fullerene-based electron acceptors, organic non-fullerene acceptors (NFAs) offer superior properties. Expanding the toolbox of all organic DCP molecules, we have developed two distinct DCPs consisting of polythiophene (PTh) photoelectron D covalently conjugated to rhodanine and perylene diimide (PDI) based organic NFAs. Grignard Metathesis (GRIM) polymerization was used to synthesize the PTh copolymer bearing protected pendant hydroxyl groups. The deprotection of pendant hydroxyl groups followed by an esterification reaction with a boronic ester (BE) bearing acid chloride produced the PTh copolymer with pendant BE groups. The subsequent Suzuki coupling reaction with 7-bromo-2,1,3-benzothiadiazole-4-carboxaldehyde (BBTCA) followed by Knoevenagel condensation with 3-ethylrhodanine produced the polythiophene-rhodanine based covalent D–A hybrid (PTh-Rho-CH) DCP. BE functionalized polythiophene (PTh-BE) was separately functionalized with a PDI derivative to synthesize a polythiophene-PDI based covalent D–A hybrid (PTh-PDI-CH) DCP. Both the DCPs exhibited strong fluorescence quenching of the polythiophene component. The synthesized DCPs were employed as the photoactive layers in interdigitated gold electrode-based photodetector devices. The application of PTh-Rho-CH and PTh-PDI-CH as photoactive layers led to a strong enhancement (by a factor of ∼8 and 16, respectively) of photocurrent generation compared to when PTh lacking acceptor species was employed as the photoactive layer. This work systematically contributes to the development of NFA-based DCPs for application in light harvesting and conversion technologies.