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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 dendronized conjugated molecules 5 and 6. (b) High-resolution STM image of the 5a monolayer on the HOPG surface. (c) Schematic model of the 5a monolayer adopting an edge-on stacking pattern, and an enlarged structural model showing hydrogen bonds by blue dashed lines. (d) Side-view model of an individual 5a molecule on the HOPG surface. (e) High-resolution STM image of 5b on the HOPG surface; inset, proposed structural model of the 5b adlayer. (f) High-resolution STM image of the self-assembly of 6 on the HOPG surface; inset, a possible packing pattern of the molecular lamellar structure of 6. Reprinted from Y Yang et al 2012 Appl. Surf. Sci.263 73, © 2012 with permission from Elsevier.
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Figure 8: (a) Chemical structures of dendronized conjugated molecules 5 and 6. (b) High-resolution STM image of the 5a monolayer on the HOPG surface. (c) Schematic model of the 5a monolayer adopting an edge-on stacking pattern, and an enlarged structural model showing hydrogen bonds by blue dashed lines. (d) Side-view model of an individual 5a molecule on the HOPG surface. (e) High-resolution STM image of 5b on the HOPG surface; inset, proposed structural model of the 5b adlayer. (f) High-resolution STM image of the self-assembly of 6 on the HOPG surface; inset, a possible packing pattern of the molecular lamellar structure of 6. Reprinted from Y Yang et al 2012 Appl. Surf. Sci.263 73, © 2012 with permission from Elsevier.

Mentions: In addition, the aligning strategy on the substrate surface constructed here has been generalized to other functional molecules. The Miao group have investigated a series of dendronized molecules 5a, 5b and 6 (figure 8(a)), which formed 2D self-organized monolayers on the HOPG surface through solution evaporation of the molecules under ambient conditions [52]. As a result of the π–π interactions, the dendronized conjugated moieties of all the compounds adopted an edge-on arrangement on the HOPG surface. Substituted by a hydroxyl group, molecule 5a stood perpendicularly to the substrate surface, resulting from both intermolecular π–π interactions and hydrogen bonding (figures 8(b)–(d)). Molecule 5b, however, attached by one long alkyl chain, was subjected not only to the π–π interactions but also to the vdW interactions of alkyl chains, as well as the interactions between the alkyl chains and the HOPG substrate. As a consequence, the alkyl chains laid flat on the substrate, while the conjugated units stood perpendicular to the HOPG surface (figure 8(e)). Compound 6 exhibited a similar 2D adsorbed structure to that of 5b, except for the slightly larger intermolecular spacing, which was due to the tilted conjugated units from the HOPG surface (figure 8(f)). In addition, both 5b and 6 displayed zigzag carbon skeletons of the alkane molecules relative to the HOPG substrate, which was due to a subtle interplay of packing and entropic effects [53].


Alkyl- π engineering in state control toward versatile optoelectronic soft materials
(a) Chemical structures of dendronized conjugated molecules 5 and 6. (b) High-resolution STM image of the 5a monolayer on the HOPG surface. (c) Schematic model of the 5a monolayer adopting an edge-on stacking pattern, and an enlarged structural model showing hydrogen bonds by blue dashed lines. (d) Side-view model of an individual 5a molecule on the HOPG surface. (e) High-resolution STM image of 5b on the HOPG surface; inset, proposed structural model of the 5b adlayer. (f) High-resolution STM image of the self-assembly of 6 on the HOPG surface; inset, a possible packing pattern of the molecular lamellar structure of 6. Reprinted from Y Yang et al 2012 Appl. Surf. Sci.263 73, © 2012 with permission from Elsevier.
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Related In: Results  -  Collection

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Figure 8: (a) Chemical structures of dendronized conjugated molecules 5 and 6. (b) High-resolution STM image of the 5a monolayer on the HOPG surface. (c) Schematic model of the 5a monolayer adopting an edge-on stacking pattern, and an enlarged structural model showing hydrogen bonds by blue dashed lines. (d) Side-view model of an individual 5a molecule on the HOPG surface. (e) High-resolution STM image of 5b on the HOPG surface; inset, proposed structural model of the 5b adlayer. (f) High-resolution STM image of the self-assembly of 6 on the HOPG surface; inset, a possible packing pattern of the molecular lamellar structure of 6. Reprinted from Y Yang et al 2012 Appl. Surf. Sci.263 73, © 2012 with permission from Elsevier.
Mentions: In addition, the aligning strategy on the substrate surface constructed here has been generalized to other functional molecules. The Miao group have investigated a series of dendronized molecules 5a, 5b and 6 (figure 8(a)), which formed 2D self-organized monolayers on the HOPG surface through solution evaporation of the molecules under ambient conditions [52]. As a result of the π–π interactions, the dendronized conjugated moieties of all the compounds adopted an edge-on arrangement on the HOPG surface. Substituted by a hydroxyl group, molecule 5a stood perpendicularly to the substrate surface, resulting from both intermolecular π–π interactions and hydrogen bonding (figures 8(b)–(d)). Molecule 5b, however, attached by one long alkyl chain, was subjected not only to the π–π interactions but also to the vdW interactions of alkyl chains, as well as the interactions between the alkyl chains and the HOPG substrate. As a consequence, the alkyl chains laid flat on the substrate, while the conjugated units stood perpendicular to the HOPG surface (figure 8(e)). Compound 6 exhibited a similar 2D adsorbed structure to that of 5b, except for the slightly larger intermolecular spacing, which was due to the tilted conjugated units from the HOPG surface (figure 8(f)). In addition, both 5b and 6 displayed zigzag carbon skeletons of the alkane molecules relative to the HOPG substrate, which was due to a subtle interplay of packing and entropic effects [53].

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.