TY - JOUR
T1 - Absence of Electrostatic Rigidity in Conjugated Polyelectrolytes with Pendant Charges
AU - Danielsen, Scott P.O.
AU - Davidson, Emily C.
AU - Fredrickson, Glenn H.
AU - Segalman, Rachel A.
N1 - Funding Information:
The authors gratefully acknowledge support from the Department of Energy (DOE) Office of Basic Energy Sciences under Grant No. DE-SC0016390. A portion of this research used neutron research facilities at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory and the National Institute of Standards and Technology, U.S. Department of Commerce, supported in part by the National Science Foundation (NSF) under Agreement No. DMR-1508249. The Materials Research Laboratory Shared Experimental Facilities are supported by the Materials Research Science and Engineering Centers Program of the NSF under Award No. DMR 1720256; a member of the NSF-funded Materials Research Facilities Network. The authors thank Dr. Alexander Mikhailovsky (UCSB) for assistance in obtaining the time-resolved photoluminescence spectroscopy measurements and Dr. Rachel Behrens (UCSB) for assistance in polymer characterization and analysis.
Publisher Copyright:
Copyright © 2019 American Chemical Society.
PY - 2019/9/17
Y1 - 2019/9/17
N2 - The delocalization of electrons in conjugated polymers impacts their chain shape, affecting their local ordering, self-assembly, and ultimately charge transport. Conjugated polyelectrolytes introduce electrostatic interactions as a molecular design parameter to potentially tune chain rigidity by combining the π-conjugated polymer backbone with pendant ionic groups. In conventional polyelectrolytes, the self-repulsion of the bound charges induce extended rod-like chain configurations. Here, we leverage small-angle neutron scattering to measure the chain shapes of model conjugated polymers in dilute solution with controlled fractions of randomly distributed pendant charges. We find these model polythiophenes are semiflexible, with a persistence length of approximately 3 nm, regardless of charge fraction, suggesting the effective absence of electrostatic rigidity in conjugated polyelectrolytes. While the overall persistence length is negligibly impacted by pendant charges, optical spectroscopy indicates that the pendant charges increase the backbone torsion between thiophene rings without significantly impacting the π-conjugation length (the length of electron delocalization along a nearly planar backbone) in dilute solution. These results indicate the effective decoupling of the pendant ionic charges from the overall chain conformation with implications for solution processing of organic semiconductors.
AB - The delocalization of electrons in conjugated polymers impacts their chain shape, affecting their local ordering, self-assembly, and ultimately charge transport. Conjugated polyelectrolytes introduce electrostatic interactions as a molecular design parameter to potentially tune chain rigidity by combining the π-conjugated polymer backbone with pendant ionic groups. In conventional polyelectrolytes, the self-repulsion of the bound charges induce extended rod-like chain configurations. Here, we leverage small-angle neutron scattering to measure the chain shapes of model conjugated polymers in dilute solution with controlled fractions of randomly distributed pendant charges. We find these model polythiophenes are semiflexible, with a persistence length of approximately 3 nm, regardless of charge fraction, suggesting the effective absence of electrostatic rigidity in conjugated polyelectrolytes. While the overall persistence length is negligibly impacted by pendant charges, optical spectroscopy indicates that the pendant charges increase the backbone torsion between thiophene rings without significantly impacting the π-conjugation length (the length of electron delocalization along a nearly planar backbone) in dilute solution. These results indicate the effective decoupling of the pendant ionic charges from the overall chain conformation with implications for solution processing of organic semiconductors.
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U2 - 10.1021/acsmacrolett.9b00551
DO - 10.1021/acsmacrolett.9b00551
M3 - Article
C2 - 35619444
AN - SCOPUS:85072581907
SN - 2161-1653
VL - 8
SP - 1147
EP - 1152
JO - ACS Macro Letters
JF - ACS Macro Letters
IS - 9
ER -