Molecular Interactions and Ordering in Electrically Doped Polymers: Blends of PBTTT and F4TCNQ

Identifying how small molecular acceptors pack with polymer donors in thin and thick (bulk) films is critical to understanding the nature of electrical doping by charge transfer. In this study, the packing structure of the molecular acceptor tetrafluorotetracyanoquinodimethane (F(4)TCNQ) with the semiconducting polymer poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno-[3,2-b]thiophene) (PBTTT-C-14) is examined. A combination of solid-state NMR, synchrotron X-ray scattering, and optical spectroscopy was used to determine the packing motif for blends of PBTTT-C-14 and F(4)TCNQ in thin and bulk films. These results indicate that F(4)TCNQ and PBTTT-C-14 order in a cofacial arrangement where charge transfer is near 100% efficient in the solid state. These results provide crucial insights into the structures and compositions of ordered domains in doped semiconducting polymers and suggest a model for the microstructure where the location of the molecular acceptors are correlated rather than randomly dispersed.