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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.


Chemical structures of C60 liquids 20–22 containing branched alkyl chains.
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Figure 17: Chemical structures of C60 liquids 20–22 containing branched alkyl chains.

Mentions: Our group has synthesized a number of liquid C60 derivatives 20–22 attached by either swallow-tail branched alkyl chains (20–21) or hyperbranched alkyl chains (22) (figure 17) [71]. Compared with the linear alkyl chain-substituted C60 derivatives 14–18, which required a 2,4,6-substitution pattern to reach a room-temperature liquid state, both 20 and 21 needed only two branched chains to generate room-temperature liquids. More significantly, 20 and 21 exhibited not only lower melting points (<−120 °C) but also less viscosity than 14–18. This was because in the case of branched chains, both the vdW interaction of the chains and the π–π interaction among the C60 moieties were strikingly suppressed. Interestingly, the viscosity of 21 (∼260 Pa · s) turned out to be much lower than that of 20 (∼1500 Pa · s) even though 21 had shorter branched alkyl chains. This finding emphasized the importance of substitution at the 2-position on the phenyl unit to produce less viscous C60 liquids.


Alkyl- π engineering in state control toward versatile optoelectronic soft materials
Chemical structures of C60 liquids 20–22 containing branched alkyl chains.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 17: Chemical structures of C60 liquids 20–22 containing branched alkyl chains.
Mentions: Our group has synthesized a number of liquid C60 derivatives 20–22 attached by either swallow-tail branched alkyl chains (20–21) or hyperbranched alkyl chains (22) (figure 17) [71]. Compared with the linear alkyl chain-substituted C60 derivatives 14–18, which required a 2,4,6-substitution pattern to reach a room-temperature liquid state, both 20 and 21 needed only two branched chains to generate room-temperature liquids. More significantly, 20 and 21 exhibited not only lower melting points (<−120 °C) but also less viscosity than 14–18. This was because in the case of branched chains, both the vdW interaction of the chains and the π–π interaction among the C60 moieties were strikingly suppressed. Interestingly, the viscosity of 21 (∼260 Pa · s) turned out to be much lower than that of 20 (∼1500 Pa · s) even though 21 had shorter branched alkyl chains. This finding emphasized the importance of substitution at the 2-position on the phenyl unit to produce less viscous C60 liquids.

View Article: PubMed Central - PubMed

ABSTRACT

Organic &pi;-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 &pi; units were in most cases attached by alkyl chains through chemical modification. Considerable numbers of alkylated-&pi; 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-&pi; molecules with emphasis on the interplay of van der Waals interactions (vdW) of the alkyl chains and &pi;&ndash;&pi; interactions of the &pi; moieties. Based on our comprehensive investigations of the two interactions&rsquo; impacts on the physical states of the molecules, a clear guidance for state control by alkyl-&pi; engineering is proposed. Specifically, either with proper alkyl chain substitution or favorable additives, the vdW and &pi;&ndash;&pi; 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-&pi; chemistry toward wide-spread applications in optoelectronic devices.

No MeSH data available.