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Effect of Chiral 2-ethylhexyl Side Chains on Chiroptical Properties of the Narrow Bandgap Conjugated Polymers PCPDTBT and PCDTPT

Effect of Chiral 2-ethylhexyl Side Chains on Chiroptical Properties of the Narrow Bandgap Conjugated Polymers PCPDTBT and PCDTPT

Stephanie L Fronk, Ming Wang, Michael Ford, Jessica Coughlin, Cheng-Kang Mai, Guillermo C Bazan

Chem Sci. 2016 Aug 1;7(8):5313-5321.

PMID: 30155183

Abstract:

Two narrow bandgap conjugated polymers containing chiral 2-ethylhexyl side chains were synthesized: poly[(4,4-bis(2-ethylhexyl)cyclopenta-[2,1-b:3,4-b']dithiophene)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PCPDTBT*) and poly[(4,4-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b0]dithiophene)-2,6-diyl-alt-[1,2,5]-thiadiazolo[3,4-c]pyridine] (PCDTPT*). The presence of a chiral substituent provides a handle to study the geometry of interchain aggregates and/or the secondary structure of these conjugated polymers in solution and in thin films via circular dichroism (CD) spectroscopy, provided that the asymmetry in the side-chain is translated to the optically active conjugated backbone. CD signals are observed for PCPDTBT* and PCDTPT* in poor solvent systems, which indicate the presence of chiral ordering in the aggregates. PCPDTBT* shows greater chiral order than PCDTPT* based on their relative anisotropy factors. Additionally, GIWAXS analysis reveals that PCPDTBT* films are more ordered than what is observed for the same polymer containing racemic 2-ethylhexyl chains. Upon solution deposition, the chiral ordering is found to translate to the solid-state microstructure for PCPDTBT* but not PCDTPT*. The presence of a pyridyl nitrogen on the thiadiazolo[3,4-c]pyridine ring of PCDTPT* favors a planar conformation for the backbone such that it has a higher rotational barrier compared to PCPDTBT*. This larger rotational barrier appears to limit the ability of PCDTPT* to adopt a helical structure or relevant chain distortions for achieving chiral aggregates.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP920515340	PCPDTBT		920515-34-0	Price

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