Synthesis of Pyrene-Substituted Poly(3-hexylthiophene) via Postpolymerization and Its Noncovalent Interactions with Single-Walled Carbon Nanotubes

Abstract

A novel pyrene-functionalized poly(3-hexylthiophene) (P3HT) derivative (<b>Pyrene-P3HT</b>) has been successfully synthesized via a postpolymerization approach, and its noncovalent interactions with SWNTs are studied in detail based on its composite of SWNT (SWNT/<b>Pyrene-P3HT</b>). The molecular structure of <b>Pyrene-P3HT</b> is confirmed by ¹H NMR spectroscopy, revealing a ca. 15% substitution ratio of pyrene within <b>Pyrene-P3HT</b>. The noncovalent interactions between SWNT and <b>Pyrene-P3HT</b> are studied by UV−vis/NIR and Raman spectroscopy as well as ESR spectroelectrochemical experiments and compared to those between SWNT and P3HT. The UV−vis/NIR spectra of SWNT/<b>Pyrene-P3HT</b> are found to be independent of the blending ratio of SWNTs and <b>Pyrene-P3HT</b>, indicating that the electronic structures of SWNTs are basically intact after blending <b>Pyrene-P3HT</b>. Raman spectra of SWNT/<b>Pyrene-P3HT</b> and SWNT/P3HT are quite different, pointing to their difference on the interactions between SWNTs and P3HT. The in situ ESR spectroelectrochemical study of SWNT/<b>Pyrene-P3HT</b> reveals that <b>Pyrene-P3HT</b> interacts with SWNTs via the noncovalent π−π bonding interactions of pyrene moieties and SWNTs and thus the attached P3HT main chain is prevented from any further interaction with the surface of SWNTs. These studies reveal the remarkable difference on the interactions between SWNTs and P3HT within SWNT/<b>Pyrene-P3HT</b> and SWNT/P3HT composites. The fluorescence intensity of SWNT/<b>Pyrene-P3HT</b> is quenched by nearly 100% compared to that of <b>Pyrene-P3HT</b>, suggesting that a strong photoinduced electron transfer resulting from the noncovalent linkage of SWNTs to the P3HT backbone via the pyrene bridge takes place upon photoexcitation. Finally, the SEM study on the film morphology of SWNT/<b>Pyrene-P3HT</b>-1 shows that the bundles of SWNTs become bigger and fewer compared to the pristine SWNTs, and the further increase of the content of <b>Pyrene-P3HT</b> within SWNT/<b>Pyrene-P3HT</b> leads to the formation of smooth film, suggesting that SWNTs are well dispersed in THF by <b>Pyrene-P3HT</b>, as confirmed by TEM study.