Microstructural Variation upon Introducing Di([2,2′-bithiophen]-5-yl)pyrenes into a Naphthalene Diimide-Based Polymer

TL;DR

This paper studies how adding different pyrene-based molecules affects the structure and performance of a polymer used in electronic devices.

Contribution

The study reveals how regioisomerism and molecular design influence the microstructure and electron mobility of a naphthalene diimide-based polymer.

Findings

Regioisomerism significantly influences the crystallization and aggregation of the polymer.

Pyrene enhances polymer backbone rigidification through naphthalene diimide–pyrene interactions.

Blends can exhibit higher electron mobility than the pure polymer.

Abstract

Four pyrene-based conjugated molecules1,6-bis­(bithiophene)­pyrene
(A), 1,6-bis­[5-octyl-(2,2′-bithiophen)-5′-yl]­pyrene
(B), 2,7-bis­[5-octyl-(2,2′-bithiophen)-5′-yl]­pyrene
(C), and 4,9-bis­[5-octyl-(2,2′-bithiophen)-5′-yl]­pyrene
(D)have been designed, synthesized, and blended
with poly­[[1,2,3,6,7,8-hexahydro-2,7-bis­(2-octyldodecyl)-1,3,6,8-dioxobenzo­[lmn]­[3,8]­phenanthroline-4,9-diyl]­[2,2′-bithiophene]-5,5′-diyl]
(P­(NDI2OD-T2, P). The structural difference between A and B lies in the presence of an alkyl substituent,
while B, C, and D are regioisomers.
The effects of the alkyl substituent and regioisomerism on the microstructure
of P have been investigated. Differential scanning calorimetry
and 1H NMR spectroscopy suggest that alkyl substitution
may not play a significant role in determining the crystallization
and aggregation of P. In contrast, regioisomerism significantly
influences these properties. Grazing-incidence X-ray scattering indicates
that while the alkyl substituent affects lamellar stacking, regioisomerism
plays a crucial role in shaping the polymer’s microstructure.
The introduction of pyrene enhances polymer backbone rigidification,
likely due to the establishment of naphthalene diimide–pyrene
interactions, as supported by density functional theory calculations.
Organic field-effect transistor measurements reveal that the blends
can exhibit higher electron mobility (μe) than P. Linear regression analysis suggests that the crystallization
of P is correlated with μe. Lastly,
the current blending approach is compared with the previous incorporation
approach, highlighting the role of molecular degrees of freedom in
contributing to the observed differences.

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