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

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.


Chemical structure of a carbazole liquid 29.
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Figure 22: Chemical structure of a carbazole liquid 29.

Mentions: Through attachment of a 2-C2C6 chain to the nitrogen atom, a room-temperature carbazole liquid 29 (figure 22) was obtained, which was employed as a ‘solvent’ in the ellipsometry measurement for the determination of electric-field-induced birefringence in photorefractive polymer composites [94]. Later, the Wada group investigated the hole mobility of 29, which was determined to be 4 × 10−6 cm2 V−1 s−1 by TOF experiment [95]. More recently, the Adachi group applied 29 as a liquid-emitting layer in organic light-emitting diodes (OLED) [96]. Such liquid emitters, although suffering inevitable long-term degradation in an OLED, could be facilely replaced by a flow of fresh ones, which effectively solved the problem of OLED degradation resulting from the decomposition of organic materials. Moreover, even with significant device bending, the detachment between the liquid-emitting layer and electrodes could be completely avoided, allowing the realization of flexible displays. Significantly, by doping a small amount of electrolytes into the liquid-emitting layer to decrease the driving voltage and by inserting a TiO2 hole-blocking layer to improve the carrier balance, the liquid OLED exhibited a maximum external electroluminescence (EL) quantum yield of 0.31 ± 0.07% and a maximum luminance of nearly 100 cd m−2.


Alkyl- π engineering in state control toward versatile optoelectronic soft materials
Chemical structure of a carbazole liquid 29.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 22: Chemical structure of a carbazole liquid 29.
Mentions: Through attachment of a 2-C2C6 chain to the nitrogen atom, a room-temperature carbazole liquid 29 (figure 22) was obtained, which was employed as a ‘solvent’ in the ellipsometry measurement for the determination of electric-field-induced birefringence in photorefractive polymer composites [94]. Later, the Wada group investigated the hole mobility of 29, which was determined to be 4 × 10−6 cm2 V−1 s−1 by TOF experiment [95]. More recently, the Adachi group applied 29 as a liquid-emitting layer in organic light-emitting diodes (OLED) [96]. Such liquid emitters, although suffering inevitable long-term degradation in an OLED, could be facilely replaced by a flow of fresh ones, which effectively solved the problem of OLED degradation resulting from the decomposition of organic materials. Moreover, even with significant device bending, the detachment between the liquid-emitting layer and electrodes could be completely avoided, allowing the realization of flexible displays. Significantly, by doping a small amount of electrolytes into the liquid-emitting layer to decrease the driving voltage and by inserting a TiO2 hole-blocking layer to improve the carrier balance, the liquid OLED exhibited a maximum external electroluminescence (EL) quantum yield of 0.31 ± 0.07% and a maximum luminance of nearly 100 cd m−2.

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.