Energy Transfer from Fluorene Based Conjugated Polyelectrolytes to Onchain and Self-Assembled Porphyrin Units

Abstract

A new water soluble fluorene-based polyelectrolyte containing on-chain porphyrin units has been synthesized via Suzuki coupling, for use in optoelectronic devices. The material consist of a random copolymer of poly{1,4-phenylene-[9,9-bis(4-phenoxy butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) and a 5,15-diphenylporphyrin (DPP). The energy transfer process between the PBS-PFP units and the porphyrin has been investigated through steady state and time-resolved measurements. The copolymer PBS-PFP-DPP displays two different emissions one located in the blue region of the spectra, corresponding to the fluorene part and another in the red due to fluorescent DPP units either formed directly or by exciton transfer. However, relatively inefficient energy transfer from the PFP to the on-chain porphyrin units was observed. We compare this with a system involving an anionic blue light-emitting donor PBS-PFP and a anionic red light-emitting energy acceptor meso-tetrakisphenylporphyrinsulfonate (TPPS), self-assembled by electrostatic attraction induced by Ca2+. Based on previous studies related to chain aggregation of the anionic copolymer PBS-PFP, two different solvent media were chosen to further explore the possibilities of the self-assembled system: dioxane–water and aqueous nonionic surfactant n-dodecylpentaoxyethylene glycol ether (C12E5). In contrast, with the on-chain PBS-PFP-DPP system the strong overlap of the 0-0 emission peak of the PBS-PFP and the Soret absorption band of the TPPS results in an efficient Förster transfer. This is strongly dependent on the solvent medium used.