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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.

No MeSH data available.


(a) Chemical structures of C60 derivatives 11a-11c containing branched alkyl chains. POM images of 11a (b), 11b (c) and 11c (d) taken in their mesophases. (e) Schematic of the BHJ cell. (f) J(V) curves of binary mixtures of PCBM/P3HT (curve i), 11a/P3HT (curve ii) and 3a/P3HT (curve iii), respectively. Reprinted from [71].
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Figure 13: (a) Chemical structures of C60 derivatives 11a-11c containing branched alkyl chains. POM images of 11a (b), 11b (c) and 11c (d) taken in their mesophases. (e) Schematic of the BHJ cell. (f) J(V) curves of binary mixtures of PCBM/P3HT (curve i), 11a/P3HT (curve ii) and 3a/P3HT (curve iii), respectively. Reprinted from [71].

Mentions: Figure 13(a) shows three C60 derivatives 11a-11c substituted by branched alkyl chains, all of which exhibited a thermotropic smectic phase observed by POM (figures 13(b)–(d)) [71]. Compound 11a with branched 2-octyldodecyl (2-C8C12) chains had a mesophase to isotropic phase transition at 84 °C, which was much lower than that of compound 3a (193 °C) attached by linear eicosyl (n-C20H41) chains, indicating the better softening effect and lower crystalline tendency of branched chains. With shorter branched chains, compound 11b (2-C6C10) exhibited a mesophase-to-isotropic phase transition at 148 °C, which is 64 °C higher than that of 11a. In sharp contrast, with linear chains, molecule 1a (n-C16H33) only showed a 30 °C increase of such a phase transition compared with 3a, proving the stronger ability of branched chains to regulate the thermotropic behavior of alkylated π molecules. Moreover, by simply changing the substitution position of 11a from (3-, 5-) positions to (3-, 4-) positions, the resulting compound 11c showed a drastic increase in the phase transition temperature (196.2 °C), which was attributed to the greater vdW interaction caused by densely packed alkyl chains. As a result, chain length, substitution position and branched extent have all played significant roles in the thermotropic behavior of the alkylated C60 derivatives.


Alkyl- π engineering in state control toward versatile optoelectronic soft materials
(a) Chemical structures of C60 derivatives 11a-11c containing branched alkyl chains. POM images of 11a (b), 11b (c) and 11c (d) taken in their mesophases. (e) Schematic of the BHJ cell. (f) J(V) curves of binary mixtures of PCBM/P3HT (curve i), 11a/P3HT (curve ii) and 3a/P3HT (curve iii), respectively. Reprinted from [71].
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Related In: Results  -  Collection

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Figure 13: (a) Chemical structures of C60 derivatives 11a-11c containing branched alkyl chains. POM images of 11a (b), 11b (c) and 11c (d) taken in their mesophases. (e) Schematic of the BHJ cell. (f) J(V) curves of binary mixtures of PCBM/P3HT (curve i), 11a/P3HT (curve ii) and 3a/P3HT (curve iii), respectively. Reprinted from [71].
Mentions: Figure 13(a) shows three C60 derivatives 11a-11c substituted by branched alkyl chains, all of which exhibited a thermotropic smectic phase observed by POM (figures 13(b)–(d)) [71]. Compound 11a with branched 2-octyldodecyl (2-C8C12) chains had a mesophase to isotropic phase transition at 84 °C, which was much lower than that of compound 3a (193 °C) attached by linear eicosyl (n-C20H41) chains, indicating the better softening effect and lower crystalline tendency of branched chains. With shorter branched chains, compound 11b (2-C6C10) exhibited a mesophase-to-isotropic phase transition at 148 °C, which is 64 °C higher than that of 11a. In sharp contrast, with linear chains, molecule 1a (n-C16H33) only showed a 30 °C increase of such a phase transition compared with 3a, proving the stronger ability of branched chains to regulate the thermotropic behavior of alkylated π molecules. Moreover, by simply changing the substitution position of 11a from (3-, 5-) positions to (3-, 4-) positions, the resulting compound 11c showed a drastic increase in the phase transition temperature (196.2 °C), which was attributed to the greater vdW interaction caused by densely packed alkyl chains. As a result, chain length, substitution position and branched extent have all played significant roles in the thermotropic behavior of the alkylated C60 derivatives.

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.