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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.


Polarized optical microscopy images of 3a at 190 °C (a), 1a at 202 °C (b) and 3b at 200 °C (c) upon cooling from the isotropic state. (d) XRD patterns of 3a at 185 °C. Reprinted with permission from T Nakanishi et al 2008 J. Am. Chem. Soc.130 9236, © 2008 American Chemical Society. (e) Proposed lamellar organization of 3a (redrawn from [70]).
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Figure 12: Polarized optical microscopy images of 3a at 190 °C (a), 1a at 202 °C (b) and 3b at 200 °C (c) upon cooling from the isotropic state. (d) XRD patterns of 3a at 185 °C. Reprinted with permission from T Nakanishi et al 2008 J. Am. Chem. Soc.130 9236, © 2008 American Chemical Society. (e) Proposed lamellar organization of 3a (redrawn from [70]).

Mentions: In spite of the promising semiconducting properties of C60, C60-containing thermotropic LCs are seldom reported, not to mention their low carrier mobility due to their moderately ordered structure and low content of C60 in the mesophase [68]. In view of the high C60 content of our alkylated-C60, based on the compact molecular design, the thermal properties of the above-mentioned C60 derivatives were investigated. 1a, 3a and 3b exhibited thermotropic polymorphism and showed unprecedentedly advantageous carrier mobility in their thermotropic mesophase [69]. For all three compounds, two endothermic peaks corresponding to crystalline-to-mesomorphic and mesomorphic-to-isotropic phase transitions were observed from differential scanning calorimetry (DSC) analysis upon heating of each sample. The thermotropic mesophase of 3a formed in a temperature range from 62 °C to 193 °C, within which an optical texture exhibiting birefringence and fluid nature was observed under polarized optical microscopy (POM) (figure 12(a)). 1a and 3b showed similar LC characteristics in temperature ranges from 33 °C to 223 °C (figure 12(b)) and from 44 °C to 226 °C (figure 12(c)), respectively. Significantly, the mesophase of 3a was able to retain the electrochemical and photoconductive properties of pristine C60, featuring both reversible electrochemistry (Ered,1 = −0.70 V and Ered,2 = −0.87 V versus Ag/AgCl) above the crystalline-to-liquid-crystalline transition temperature (62 °C) and relatively high electron mobility of ∼3 × 10−3 cm2 V−1 s−1 at 120 °C, evaluated by a conventional time-of-flight (TOF) set-up.


Alkyl- π engineering in state control toward versatile optoelectronic soft materials
Polarized optical microscopy images of 3a at 190 °C (a), 1a at 202 °C (b) and 3b at 200 °C (c) upon cooling from the isotropic state. (d) XRD patterns of 3a at 185 °C. Reprinted with permission from T Nakanishi et al 2008 J. Am. Chem. Soc.130 9236, © 2008 American Chemical Society. (e) Proposed lamellar organization of 3a (redrawn from [70]).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 12: Polarized optical microscopy images of 3a at 190 °C (a), 1a at 202 °C (b) and 3b at 200 °C (c) upon cooling from the isotropic state. (d) XRD patterns of 3a at 185 °C. Reprinted with permission from T Nakanishi et al 2008 J. Am. Chem. Soc.130 9236, © 2008 American Chemical Society. (e) Proposed lamellar organization of 3a (redrawn from [70]).
Mentions: In spite of the promising semiconducting properties of C60, C60-containing thermotropic LCs are seldom reported, not to mention their low carrier mobility due to their moderately ordered structure and low content of C60 in the mesophase [68]. In view of the high C60 content of our alkylated-C60, based on the compact molecular design, the thermal properties of the above-mentioned C60 derivatives were investigated. 1a, 3a and 3b exhibited thermotropic polymorphism and showed unprecedentedly advantageous carrier mobility in their thermotropic mesophase [69]. For all three compounds, two endothermic peaks corresponding to crystalline-to-mesomorphic and mesomorphic-to-isotropic phase transitions were observed from differential scanning calorimetry (DSC) analysis upon heating of each sample. The thermotropic mesophase of 3a formed in a temperature range from 62 °C to 193 °C, within which an optical texture exhibiting birefringence and fluid nature was observed under polarized optical microscopy (POM) (figure 12(a)). 1a and 3b showed similar LC characteristics in temperature ranges from 33 °C to 223 °C (figure 12(b)) and from 44 °C to 226 °C (figure 12(c)), respectively. Significantly, the mesophase of 3a was able to retain the electrochemical and photoconductive properties of pristine C60, featuring both reversible electrochemistry (Ered,1 = −0.70 V and Ered,2 = −0.87 V versus Ag/AgCl) above the crystalline-to-liquid-crystalline transition temperature (62 °C) and relatively high electron mobility of ∼3 × 10−3 cm2 V−1 s−1 at 120 °C, evaluated by a conventional time-of-flight (TOF) set-up.

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.