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Alkyl- π engineering in state control toward versatile optoelectronic soft materials

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ABSTRACT

Organic π-conjugated molecules with extremely rich and tailorable electronic and optical properties are frequently utilized for the fabrication of optoelectronic devices. To achieve high solubility for facile solution processing and desirable softness for flexible device fabrication, the rigid π units were in most cases attached by alkyl chains through chemical modification. Considerable numbers of alkylated-π molecular systems with versatile applications have been reported. However, a profound understanding of the molecular state control through proper alkyl chain substitution is still highly demanded because effective applications of these molecules are closely related to their physical states. To explore the underlying rule, we review a large number of alkylated-π molecules with emphasis on the interplay of van der Waals interactions (vdW) of the alkyl chains and π–π interactions of the π moieties. Based on our comprehensive investigations of the two interactions’ impacts on the physical states of the molecules, a clear guidance for state control by alkyl-π engineering is proposed. Specifically, either with proper alkyl chain substitution or favorable additives, the vdW and π–π interactions can be adjusted, resulting in modulation of the physical states and optoelectronic properties of the molecules. We believe the strategy summarized here will significantly benefit the alkyl-π chemistry toward wide-spread applications in optoelectronic devices.

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(a) Chemical structures of HBC derivatives 12a–12b containing branched alkyl chains. POM images of 12a (b) and 12b (c) obtained after cooling from the isotropic state. Reprinted with permission from M Kastler et al 2006 Adv. Mater. 18 2255, © 2006 John Wiley & Sons .
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Figure 14: (a) Chemical structures of HBC derivatives 12a–12b containing branched alkyl chains. POM images of 12a (b) and 12b (c) obtained after cooling from the isotropic state. Reprinted with permission from M Kastler et al 2006 Adv. Mater. 18 2255, © 2006 John Wiley & Sons .

Mentions: Müllen and his coworkers have reported a number of thermotropic LCs based on HBC derivatives substituted with both linear [73, 82] and branched alkyl chains [83, 84] (figure 14). All the linear alkyl chain-substituted HBC derivatives, together with the short branched alkyl chain-equipped HBC compound 12a, exhibited a crystalline-to-LC phase transition around 100 °C and a LC-to-isotropic phase transition around 420 °C. In dramatic contrast, the long-branched alkyl chain-modified HBC derivative, 12b, displayed much lower phase transitions with a crystalline-to-LC phase transition at 17 °C and LC-to-isotropic phase transition at 97 °C, which further confirmed the more profound softening effect of branched chains and their stronger ability to regulate and adjust the thermotropic behavior. At room temperature, the charge carrier mobility for 12b was determined to be 0.73 cm2 V−1 s−1, representing the highest value measured for a noncrystalline discotic LC material.


Alkyl- π engineering in state control toward versatile optoelectronic soft materials
(a) Chemical structures of HBC derivatives 12a–12b containing branched alkyl chains. POM images of 12a (b) and 12b (c) obtained after cooling from the isotropic state. Reprinted with permission from M Kastler et al 2006 Adv. Mater. 18 2255, © 2006 John Wiley & Sons .
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC5036497&req=5

Figure 14: (a) Chemical structures of HBC derivatives 12a–12b containing branched alkyl chains. POM images of 12a (b) and 12b (c) obtained after cooling from the isotropic state. Reprinted with permission from M Kastler et al 2006 Adv. Mater. 18 2255, © 2006 John Wiley & Sons .
Mentions: Müllen and his coworkers have reported a number of thermotropic LCs based on HBC derivatives substituted with both linear [73, 82] and branched alkyl chains [83, 84] (figure 14). All the linear alkyl chain-substituted HBC derivatives, together with the short branched alkyl chain-equipped HBC compound 12a, exhibited a crystalline-to-LC phase transition around 100 °C and a LC-to-isotropic phase transition around 420 °C. In dramatic contrast, the long-branched alkyl chain-modified HBC derivative, 12b, displayed much lower phase transitions with a crystalline-to-LC phase transition at 17 °C and LC-to-isotropic phase transition at 97 °C, which further confirmed the more profound softening effect of branched chains and their stronger ability to regulate and adjust the thermotropic behavior. At room temperature, the charge carrier mobility for 12b was determined to be 0.73 cm2 V−1 s−1, representing the highest value measured for a noncrystalline discotic LC material.

View Article: PubMed Central - PubMed

ABSTRACT

Organic π-conjugated molecules with extremely rich and tailorable electronic and optical properties are frequently utilized for the fabrication of optoelectronic devices. To achieve high solubility for facile solution processing and desirable softness for flexible device fabrication, the rigid π units were in most cases attached by alkyl chains through chemical modification. Considerable numbers of alkylated-π molecular systems with versatile applications have been reported. However, a profound understanding of the molecular state control through proper alkyl chain substitution is still highly demanded because effective applications of these molecules are closely related to their physical states. To explore the underlying rule, we review a large number of alkylated-π molecules with emphasis on the interplay of van der Waals interactions (vdW) of the alkyl chains and π–π interactions of the π moieties. Based on our comprehensive investigations of the two interactions’ impacts on the physical states of the molecules, a clear guidance for state control by alkyl-π engineering is proposed. Specifically, either with proper alkyl chain substitution or favorable additives, the vdW and π–π interactions can be adjusted, resulting in modulation of the physical states and optoelectronic properties of the molecules. We believe the strategy summarized here will significantly benefit the alkyl-π chemistry toward wide-spread applications in optoelectronic devices.

No MeSH data available.