Azulene-based conjugated polymers: unique seven-membered ring connectivity leading to stimuli-responsiveness

Murai, Masahito; Amir, Elizabeth; Amir, Roey J.; Hawker, Craig J.

doi:10.1039/c2sc20615c

Cited by 79 publications

(58 citation statements)

References 45 publications

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“…Mater. [ 34,44,45 ] Consistent with these observations, we found that the original properties of the copolymers could be recovered after neutralization of the acidic polymer solutions. Interestingly, a strong solvatochromic effect was also observed with signifi cant emission occurring from THF solutions compared to only weak fl uorescence of the polymers in chloroform.…”

Section: Resultssupporting

confidence: 86%

“…[33][34][35][36] Despite its potential, most materials incorporating azulene as a building block have been limited to functionalization by various electrophilic transformations, leading to oligomers and polymers with the azulene nucleus connected exclusively through the 5-membered ring (1,3-connectivity). [ 44,45 ] Building on these fi ndings, the combination of both the 1,3-and 4,7-regioisomers of azulene could have important implications for materials design. [ 44,45 ] Building on these fi ndings, the combination of both the 1,3-and 4,7-regioisomers of azulene could have important implications for materials design.…”

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confidence: 99%

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Modulating the Properties of Azulene‐Containing Polymers through Controlled Incorporation of Regioisomers

Tsurui

Murai

et al. 2014

Adv Funct Materials

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wileyonlinelibrary.comits constitutional isomer, naphthalene, azulene is a bright blue compound that exhibits large dipolar character (1.08 D) due to resonance delocalization that results in an electron-rich 5-membered ring and an electron-poor 7-membered ring. [23][24][25] The unique photophysical properties of azulene arise from a dissimilar distribution of electron density between the HOMO and LUMO leading to a relatively small electron repulsion energy in the fi rst excited singlet state. [ 25 ] These attributes, coupled with its stimuli-responsive behavior in acidic environments, make azulene a promising building block for the construction of new conjugated polymers with unique properties. [26][27][28][29] Responsive materials that exhibit dramatic changes in optical properties upon the introduction of external stimuli are promising for a number of applications including sensing technologies. [30][31][32] In the case of azulene-containing materials, protonation leads to the formation of a stable tropylium cation with signifi cantly different spectroscopic properties than the neutral species. [33][34][35][36] Despite its potential, most materials incorporating azulene as a building block have been limited to functionalization by various electrophilic transformations, leading to oligomers and polymers with the azulene nucleus connected exclusively through the 5-membered ring (1,3-connectivity). [37][38][39][40][41][42][43] We recently demonstrated that azulene-based materials connected through the electron-poor 7-membered ring (4,7-connectivity) exhibit unique properties, in part due to the conservation of π-conjugation after protonation. [ 44,45 ] Building on these fi ndings, the combination of both the 1,3-and 4,7-regioisomers of azulene could have important implications for materials design. In analogy to random D-A copolymers that comprise multiple types of randomly distributed donor and/or acceptor units, [ 13,[46][47][48][49][50][51][52] we hypothesized that conjugated polymers with tunable electronic properties could be accessed by incorporation of different regioisomeric azulene building blocks in which their connectivity (electron-rich or electron-poor 5-and 7-membered rings) is varied along the polymer chain.Herein, we describe the synthesis and evaluation of a series of random copolymers incorporating the azulene building block with varying ratios of 1,3-and 4,7-connectivity. Both bithiophene and fl uorene comonomers were investigated leading to two new libraries of random conjugated copolymers. Signifi cantly, we demonstrate that the optoelectronic properties Two libraries of random conjugated polymers are presented that incorporate varying ratios of regioisomeric azulene units connected via the 5-membered or 7-membered ring in combination with bithiophene or fl uorene comonomers. It is demonstrated that the optoelectronic and stimuli-responsive properties of the materials can be systematically modulated by tuning the relative percentage of each azulene building block in the polymer backbone. Signi...

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Section: Resultssupporting

confidence: 86%

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confidence: 99%

Modulating the Properties of Azulene‐Containing Polymers through Controlled Incorporation of Regioisomers

Tsurui

Murai

et al. 2014

Adv Funct Materials

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“…Moreover, polyazulenes with a seven‐membered ring structure are valuable for the formation and stabilization of azulenium cations. [ 49 ] Poly(4,7‐azulenes) ( P2 – P4 ) have been synthesized through the Yamamoto coupling of 4,7‐dibromoazulenes ( Figure a). The extended conjugation effectively stabilizes P2 – P4 through substitutions on the seven‐membered ring (Figure 8b).…”

Section: Linear Polymersmentioning

confidence: 99%

Azulene‐Based Molecules, Polymers, and Frameworks for Optoelectronic and Energy Applications

Huang

Zhao

et al. 2020

Small Methods

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has a large dipole moment of 1.08 D. [2] By contrast, naphthalene, which only contains two fused six-membered rings, has a dipole moment of 0 D. Azulene, which was discovered and named by Piesse in 1863, has attracted considerable interest since its discovery in petroleum exploitation. [3] In 1937, Plattner and Pfau published their pioneering report on the synthesis of azulene. [4] However, their method was not practical due to its low azulene yield. In the 1950s, Ziegler and Hafner formulated a highly efficient and practical method for synthesizing azulene and its derivatives. [5] Because azulene is difficult to synthesize and has a low natural abundance, research on azulene-based molecules and materials is less advanced relative to research on its isomer. Direct functionalization of 1-and/ or 3-positions is a common and effective method of producing azulene derivatives. However, direct functionalization of other positions is much harder, e.g., bromination of 6-and 1,3-positions, [6] nucleophilic addition to obtain 6-subsituted azulene, [7] borylation at 2-position, [8] arylation at the 2-position, [9] and so on. The electron distribution in the front-line molecular orbitals (MOs) must usually be considered when functionalizing azulene. Because of resonance delocalization, the oddnumbered position of azulene, which is electron-rich, easily reacts with electrophilic compounds. Among the odd-numbered azulene varieties, 1-and 3-azulene have the highest activity. [10] By Azulene has a considerably larger dipole moment than its isomer naphthalene; it also has unique physicochemical properties, including different reactivities on five-and seven-membered rings, a dark color, a narrow gap between the highest occupied molecular orbital and lowest unoccupied molecular orbital, and stimulus response. Although azulene was discovered more than 100 years ago, the use of azulene-based derivatives can be traced back to five centuries ago. Due to its unusual structure, azulene-based molecules and materials are widely used in various fields. However, studies on azulene-based materials have long been hindered by difficulties in the synthesis. Considerably fewer studies have been conducted on azulene-based derivatives than on naphthalene-based derivatives. This perspective paper mainly introduces recent reports on the synthesis of azulene-based aromatic molecules, conjugated polymers, and coordination polymers, in addition to azulene-based frameworks. The structure-property relationship, optoelectronic applications, and energy-related applications of azulene-based derivatives are reviewed, including their use in near-infrared absorption, organic field-effect transistors, organic solar cells, and microsupercapacitors.

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“…By far the most abundant connection to prepare azulene materials is through the 1,3 positions as established initially through electropolymerization and since used for homo and copolymer studies . Other connections have emerged recently, such as Craig Hawker's azulene‐4,7‐diyl copolymers and Jun‐ichiro Kitai et al. 's 5,6‐linked molecular photochromes .…”

Section: Hückel's N = 2: Azulenementioning

confidence: 99%

Prospecting in Hückel‐space: From Hinokitiol to Non‐benzenoid Organic Electronics

Tovar

2014

The Chemical Record

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Azulene-based conjugated polymers: unique seven-membered ring connectivity leading to stimuli-responsiveness

Cited by 79 publications

References 45 publications

Modulating the Properties of Azulene‐Containing Polymers through Controlled Incorporation of Regioisomers

Modulating the Properties of Azulene‐Containing Polymers through Controlled Incorporation of Regioisomers

Azulene‐Based Molecules, Polymers, and Frameworks for Optoelectronic and Energy Applications

Prospecting in Hückel‐space: From Hinokitiol to Non‐benzenoid Organic Electronics

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