Breaking the Bimolecular Crystal: The Effect of Side Chain Length on Breaking the Bimolecular Crystal: The Effect of Side Chain Length on Oligothiophene/Fullerene Intercalation

Poster Session: 

A

Presenter: 

Ned Burnett

Authors: 

Ned Burnett1, Benjamin Cherniawski1, Detlef-M. Smilgies2, Sean Parkin3 ,and Alejandro L. Briseno1

Author Affiliation: 

1Polymer Science and Engineering, University of Massachusetts Amherst, 120 Governors Drive, Amherst, MA 01003, United States 2Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York 14850, United States 3Department of Chemistry, University of Kentucky, Lexington, Kentucky 40506-005, United States

Abstract: 

Polymer/fullerene bimolecular crystal formation has been investigated using a variety of conjugated polymers and fullerenes to understand the design rules that influence donor/acceptor interaction. Modifications of the polymer by varying the substitution side chain position, density, and branching have demonstrated the importance of the “pocket” dimensions (free volume between side chains where the fullerene resides) for controlling intercalation. Yet the effect of pocket height has not been systematically explored due to the solubility limitations in polymers. In this report, we present an experimental investigation into the effect of the pocket height by synthesizing poly[2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) dimers with varied side chain lengths and track the morphological changes of the dimer/fullerene blends using grazing-incidence X-ray scattering, thermal measurements, and photoluminescence quenching. We identify two regimes: 1) oligomers with side chains ≥ heptyl (C7) form bimolecular crystals and 2) oligomers with ≤ hexyl (C6) form amorphous blends. This work provides the first observation of an order-to-disorder transition mediated by side chain length in donor-fullerene intercalated blends.