Structure and Excited-State Interactions in Composites of CdSe Nanorods and Interface-Compatible Polythiophene-graft-poly(N,N-dimethylaminoethyl methacrylates)

Graphical Abstract

Comb-like graft copolymers of polythiophene-graft-poly(N,N-dimethylaminoethyl methacrylates) show enhanced interfacial compatibility when interacting with CdSe nanorods. The morphology and the internal structure of the composites vary with a change in the nanorod/polymer ratio as well as with the concentration of each component. The presence of CdSe nanorods in toluene leads to photoluminescence quenching of the polythiophene backbone in the graft copolymer with relatively short side chains.

Abstract

We report the preparation and characterization of two comb-like graft copolymers, polythiophene-graft-poly(N,N-dimethylaminoethyl methacrylates) (PT₇₀₀-g-PDMA₆₀ and PT₂₂₀-g-PDMA₁₆, where the subscripts represent the number average degree of polymerization), and an investigation of their interaction with CdSe nanorods. Each polymer contains a regiorandom polythiophene (PT) as the backbone, from which poly(N,N-dimethylaminoethyl methacrylate) (PDMA) chains are densely grafted. The PDMA arms serve as multidentate ligands for CdSe semiconductor nanocrystals and increase the compatibility between the PT backbone and the nanocrystals. Using electron microscopy, we examined the morphology and the internal structure of the nanorod/polymer composites formed in toluene. The morphology and the internal structure of the composites vary with a change in the nanorod/polymer ratio as well as with the concentration of each component. The results of steady-state fluorescence spectroscopy indicate that the presence of the nanocrystals in toluene leads to photoluminescence (PL) quenching of the PT backbone in the graft copolymer with relatively short PDMA arms (PT₂₂₀-g-PDMA₁₆). In contrast, no PL quenching could be detected in composites formed from a similar polymer with longer PDMA arms (PT₇₀₀-g-PDMA₆₀). A likely explanation of this result is that in composites formed with PT₇₀₀-g-PDMA₆₀, the nanocrystals are held too far from the PT backbone for energy transfer or charge transfer to take place.