Polyselenophenes with distinct crystallization properties

Abstract

The polythiophene derivative poly(3-hexyl)thiophene (P3HT) has become one of the most well studied organic materials due to its interesting and important chemical and physical properties. Two different crystal structures have been observed for P3HT, type-1 and type-2, however a pure type-2 structure has never been obtained. Herein, we investigate the crystal structure of polyselenophene analogs (P3HS), and discover that a pure type-2 phase is formed in low molecular weight P3HS (M_n = 5.9 kg mol⁻¹). Wide-angle X-ray scattering shows that the type-2 phase is readily formed and stable at room temperature, which is very distinct from what is observed in control experiments with P3HT. Absorption spectra of P3HS films with the pure type-2 phase lack the typical shoulder peaks indicating that π–π stacking is relatively poor in the type-2 phase. Scanning transmission electron microscopy (STEM) images, however, show that large nanofibers are formed by type-2 crystallization thereby demonstrating the potential of P3HS to drive unique types of self-assembled structures through crystallization, and should motivate continued efforts on selenophene analogs of P3HT for a variety of studies and uses.