Electron-transporting foldable alternating copolymers of perylenediimide and flexible macromolecular chains

Abstract

Tuning the electrical conductivity of conjugated macromolecules by nanostructure ordering plays a key role in developing carrier transporting materials applicable to flexible organic electronic devices. Alternating copolymers of perylene-3,4,9,10-tetracarboxylic acid diimide (PDI) and flexible macromonomers, poly(dimethylsiloxane) (PDMS), poly(ethylene glycol) (PEG), or poly(propylene glycol) (PPG), were synthesized via simple polycondensation reactions between 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and bis-amine-terminated corresponding macromonomers. Dynamic traces of absorption and fluorescence spectra of the series of alternating copolymers, with the indication of PDI chromophores, suggested the more foldable nature in tetrahydrofuran of the PDMS-based polymer than of the PEG- and PPG-based polymers. The folding capability of these polymers in solution was confirmed by fluorescence spectra and the absolute fluorescence quantum efficiency values. In the solid films, the condensed state of the polymers showed X-ray diffraction patterns of periodic structures, which depend on the type of macromolecular chains: PEG showed a highly crystallized state in contrast to the slightly crystalline PDI molecules in the PDMS and PPG-based polymers. Photoconductivity upon ultraviolet excitation has been screened by noncontact microwave measurements, and the mobility of electrons has also been characterized based on the kinetic traces of radical anions on the PDI chromophores. The negligible optical absorption observed from the PDMS-based polymers revealed the lowest photocarrier generation yield among the prepared polymers. The observed low conductivity for the PDMS-based, most foldable polymers possibly results from a lower photo-charge generation yield and thermal fluctuations of the flexible PDMS chains. The PEG-based polymer marked the largest electron mobility of 0.2 cm² V⁻¹ s⁻¹, reflecting the highly crystalline nature of the PEG chains.