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Design principle for increasing charge mobility of π-conjugated polymers using regularly localized molecular orbitals.

Terao J, Wadahama A, Matono A, Tada T, Watanabe S, Seki S, Fujihara T, Tsuji Y - Nat Commun (2013)

Bottom Line: The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires.When the length of the linear region of the zigzag wires was increased to 10 phenylene-ethynylene units, the intramolecular charge mobility increased to 8.5 cm(2) V(-1) s(-1).Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan. terao@scl.kyoto-u.ac.jp

ABSTRACT
The feasibility of using π-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of π-conjugated polymers by covering the π-conjugated chain with macrocycles and regularly localizing π-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, insulated wires containing meta-junctioned poly(phenylene-ethynylene) as the backbone units were designed and synthesized. The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires. When the length of the linear region of the zigzag wires was increased to 10 phenylene-ethynylene units, the intramolecular charge mobility increased to 8.5 cm(2) V(-1) s(-1). Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

No MeSH data available.


Syntheses of zigzag IMWs 11 and 12 with elongated para-segments between the meta-junctions.Complete experimental details and characterization are supplied in the Supplementary Methods section.
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f6: Syntheses of zigzag IMWs 11 and 12 with elongated para-segments between the meta-junctions.Complete experimental details and characterization are supplied in the Supplementary Methods section.

Mentions: Another point of interest is the dependence on para-length of the mobility in the meta-systems. To examine the effect of elongation of the length of the para-segments, zigzag IMWs 11 and 12 containing six and ten PE units between the meta-junctions, respectively, were synthesized (Fig. 6) via Sonogashira copolymerization of 5 with 1,3-diethynylbenzene (to prepare 11) and 7 with 6 (to prepare 12). Notably, when the length between the para-segments of the IMWs 10 was increased from three (10) to ten (12) PE units, the intramolecular charge mobility increased to 8.5 cm2 V−1 s−1 (Supplementary Fig. S11). In general, the cross-boundaries for the hopping and band transport of charge carriers occur when the mobility is in the range 1–10 cm2 V−1 s−1, and thus the value obtained here nearly reaches the highest limit for the mobility of charge carriers transported via inter-site hopping processes. The temperature dependence of the transient photoconductivity was also examined for 12 (Supplementary Fig. S12). The Arrhenius plot was found to have a slope with a low activation energy of 20 meV at 1/T <0.0035, even though a slightly higher energy of 40 meV was observed over the entire temperature range. The energy at the higher temperatures, which was almost equivalent to the thermal energy of electrons, strongly suggests that the charge carrier mobility occurs on the conjugated backbone of 12 in the cross-boundary range for charge carrier transport mechanisms. A much higher value of mobility, 600 cm2 V−1 s−1, has previously been reported, defined as an intramolecular mobility in the electronic band-conduction model, where the phonon scattering of the charge carriers has a negative effect on the overall transport of the charge carriers16. In the present work, hopping transport is the predominant process and 8.5 cm2 V−1 s−1 is the highest mobility value for the one-dimensional intramolecular hopping of holes along a π-conjugated polymer reported thus far25. With an electric field strength of E=25 V cm−1 used in the microwave cavity, the mean local displacement of charge carriers, dx, can be estimated as follows:


Design principle for increasing charge mobility of π-conjugated polymers using regularly localized molecular orbitals.

Terao J, Wadahama A, Matono A, Tada T, Watanabe S, Seki S, Fujihara T, Tsuji Y - Nat Commun (2013)

Syntheses of zigzag IMWs 11 and 12 with elongated para-segments between the meta-junctions.Complete experimental details and characterization are supplied in the Supplementary Methods section.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3644079&req=5

f6: Syntheses of zigzag IMWs 11 and 12 with elongated para-segments between the meta-junctions.Complete experimental details and characterization are supplied in the Supplementary Methods section.
Mentions: Another point of interest is the dependence on para-length of the mobility in the meta-systems. To examine the effect of elongation of the length of the para-segments, zigzag IMWs 11 and 12 containing six and ten PE units between the meta-junctions, respectively, were synthesized (Fig. 6) via Sonogashira copolymerization of 5 with 1,3-diethynylbenzene (to prepare 11) and 7 with 6 (to prepare 12). Notably, when the length between the para-segments of the IMWs 10 was increased from three (10) to ten (12) PE units, the intramolecular charge mobility increased to 8.5 cm2 V−1 s−1 (Supplementary Fig. S11). In general, the cross-boundaries for the hopping and band transport of charge carriers occur when the mobility is in the range 1–10 cm2 V−1 s−1, and thus the value obtained here nearly reaches the highest limit for the mobility of charge carriers transported via inter-site hopping processes. The temperature dependence of the transient photoconductivity was also examined for 12 (Supplementary Fig. S12). The Arrhenius plot was found to have a slope with a low activation energy of 20 meV at 1/T <0.0035, even though a slightly higher energy of 40 meV was observed over the entire temperature range. The energy at the higher temperatures, which was almost equivalent to the thermal energy of electrons, strongly suggests that the charge carrier mobility occurs on the conjugated backbone of 12 in the cross-boundary range for charge carrier transport mechanisms. A much higher value of mobility, 600 cm2 V−1 s−1, has previously been reported, defined as an intramolecular mobility in the electronic band-conduction model, where the phonon scattering of the charge carriers has a negative effect on the overall transport of the charge carriers16. In the present work, hopping transport is the predominant process and 8.5 cm2 V−1 s−1 is the highest mobility value for the one-dimensional intramolecular hopping of holes along a π-conjugated polymer reported thus far25. With an electric field strength of E=25 V cm−1 used in the microwave cavity, the mean local displacement of charge carriers, dx, can be estimated as follows:

Bottom Line: The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires.When the length of the linear region of the zigzag wires was increased to 10 phenylene-ethynylene units, the intramolecular charge mobility increased to 8.5 cm(2) V(-1) s(-1).Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

View Article: PubMed Central - PubMed

Affiliation: Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan. terao@scl.kyoto-u.ac.jp

ABSTRACT
The feasibility of using π-conjugated polymers as next-generation electronic materials is extensively studied; however, their charge mobilities are lower than those of inorganic materials. Here we demonstrate a new design principle for increasing the intramolecular charge mobility of π-conjugated polymers by covering the π-conjugated chain with macrocycles and regularly localizing π-molecular orbitals to realize an ideal orbital alignment for charge hopping. Based on theoretical predictions, insulated wires containing meta-junctioned poly(phenylene-ethynylene) as the backbone units were designed and synthesized. The zigzag wires exhibited higher intramolecular charge mobility than the corresponding linear wires. When the length of the linear region of the zigzag wires was increased to 10 phenylene-ethynylene units, the intramolecular charge mobility increased to 8.5 cm(2) V(-1) s(-1). Theoretical analysis confirmed that this design principle is suitable for obtaining ideal charge mobilities in π-conjugated polymer chains and that it provides the most effective pathways for inter-site hopping processes.

No MeSH data available.