Helical Sexithiophenes: An Experimental and Theoretical Study of Implicating the Alternating 2,2′:3,3′ Regioisomer as a Reliable Helical Motif.

Marsella, Michael J.; Yoon, Kunsang; Almutairi, Adah; Butt, Sheraz K.; Tham, Fook S.

doi:10.1002/chin.200409089

Cited by 3 publications

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“…Based on this model, the simulated P5HT with 16 units was optimized and found to adopt a helical structure with end units twisted, which is different from the 3 1 helical geometry of oligo(othiophene)s revealed by single X-ray analysis (Figure S9). 6 We then estimated the helical pitch of P5HT as 0.56 nm and diameter of the helix as 1.81 nm, which are consistent with the observed parameters of P5BT by STM. 68 Our simulation result further revealed that the protons on the alkyl chain carbons are oriented closer (<5 Å) to the H4 on the (same) thiophene ring.…”

Section: ■ Results and Discussionsupporting

confidence: 80%

“…Although 2,2′,3,3′-linked oligo(o-thiophene)s have been reported to adopt a helical structure based on single crystal X-ray analysis, one could not presume that 2,3-linked P5AT would necessarily adopt the same helical geometry due to the difference in ring connections and chain length. 6,35 Compared with oligomers, direct analysis of helical geometry of poly(o-arylene)s is more difficult. Although the secondary structure of poly(2,3quinoxaline)s and poly(1,10-phenanthroline-5,6-diyl)s have been experimentally studied by NMR, small-angle X-ray scattering (SAXS), and circular dichroism (CD), 31,36,37 it is still challenging to provide exact helical structure information such as helical pitch and helical sense with these methods.…”

Section: ■ Introductionmentioning

confidence: 99%

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Helical Poly(5-alkyl-2,3-thiophene)s: Controlled Synthesis and Structure Characterization

Zhang

Bonnesen

et al. 2016

Macromolecules

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Whereas poly(3-alkyl-2,5-thiophene)s (P3AT), with many potential applications, have been extensively investigated, their ortho-connected isomers, poly(5-alkyl-2,3-thiophene)s (P5AT), have never been reported because of the difficulty in their syntheses. We herein present the first synthesis of regioregular P5AT via controlled Suzuki cross-coupling polymerization with PEPPSI-IPr as catalyst, affording the polymers with tunable molecular weight, narrow polydispersity (PDI), and well-defined functional end groups at the gram scale. The helical geometry of P5AT was studied by a combination of NMR, small-angle X-ray scattering (SAXS), and scanning tunneling microscopy (STM). Particularly, the single polymer chain of poly(5-butyl-2,3-thiophene) (P5BT) on highly oriented pyrolytic graphite (HOPG) substrates with either M or P helical conformation was directly observed by STM. The comparison of UV−vis absorption between poly(5-hexyl-2,3-thiophene) (P5HT) (λ = 345 nm) and poly(3-hexyl-2,5-thiophene) (P3HT) (λ = 450 nm) indicated that the degree of conjugation of the backbone in P5HT is less than in P3HT, which may be a consequence of the helical geometry of the former compared to the more planar geometry of the latter. Moreover, we found that P5HT can emit green fluorescence under UV (λ = 360 nm) irradiation. ■ INTRODUCTIONConjugated polyarylenes have found a wide range of applications including optical sensors, electrochromic devices, field effect transistors, and organic solar cells. 1−3 Their physical properties are controlled by the manner in which their rings are connected. As a result, ortho-, meta-, and para-linked polyarylenes each show distinctive optoelectronic properties and accordingly constitute different classes of functional polymers. 4,5 Although meta-and para-linked polyarylenes have been extensively investigated over the past decades, the study of poly(o-arylene)s is still at an early stage because of the synthesis challenges.It has been reported recently that oligo(o-arylene)s intrinsically possess a compressed helical structure with a helical pitch of 0.3−0.5 nm in the solid state as revealed by single crystal X-ray analysis, including oligo(o-phenylene)s, oligo(o-thiophene)s, oligo(o-thiazole)s, and oligo(o-furan)s. 6−10 Moreover, Hartley and co-workers disclosed that this compressed helical structure of oligo(o-arylene)s is stabilized by aromatic stacking interactions, 11,12 which is different from traditional helical polymers commonly stabilized by steric effects or hydrogen bonding. 13−15 Thus, due to their helical structures, oligo(o-arylene)s are reported to possess certain unique properties with potential applications different from their meta-or para-counterparts. 16 For example, Fukushima and Aida et al. reported that oligo(ophenylene)s possessed a main chain redox active property that responded to electrical inputs by a conformation change and acted as surface modifiers for homeotropic columnar ordering of discotic liquid crystals. 8,17 Ito and co-workers reported poly-(quinoxaline-2,3-diyl)s...

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Section: ■ Results and Discussionsupporting

confidence: 80%

Section: ■ Introductionmentioning

confidence: 99%

Helical Poly(5-alkyl-2,3-thiophene)s: Controlled Synthesis and Structure Characterization

Zhang

Bonnesen

et al. 2016

Macromolecules

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“…48 Several analogues based on five-membered aromatic heterocycles have also been reported. In general, good folding may be observed in the solid state 49,50 but solution-phase behavior is complex in the absence of secondary interactions between appended units. 51 Unlike o-phenylenes, conformational exchange in oligomers of five-membered heterocycles appears to be fast on the NMR time scale.…”

Section: ■ Heterocyclic Analogues Of O-phenylenesmentioning

confidence: 99%

Folding of ortho-Phenylenes

2016

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In nature, the folding of oligomers and polymers is used to generate complex three-dimensional structures, yielding macromolecules with diverse functions in catalysis, recognition, transport, and charge- and energy-transfer. Over the past 20-30 years, chemists have sought to replicate this strategy by developing new foldamers: oligomers that fold into well-defined secondary structures in solution. A wide array of abiotic foldamers have been developed, ranging from non-natural peptides to aromatics. The ortho-phenylenes represent a recent addition to the family of aromatic foldamers. Despite their structural simplicity (chains of benzenes connected at the ortho positions), it was not until 2010 that systematic studies of o-phenylenes showed that they reliably fold into helices in solution (and in the solid state). This conformational behavior is of fundamental interest: o-Arylene and o-heteroarylene structures are found embedded within many other systems, part of an emerging interest in sterically congested polyphenylenes. Further, o-phenylenes are increasingly straightforward to synthesize because of continuing developments in arene-arene coupling, the Asao-Yamamoto benzannulation, and benzyne polymerization. In this Account, we discuss the folding of o-phenylenes with emphasis on features that make them unique among aromatic foldamers. Interconversion between their different backbone conformers is slow on the NMR time scale around room temperature. The (1)H NMR spectra of oligomers can therefore be deconvoluted to give sets of chemical shifts for different folding states. The chemical shifts are both highly sensitive to conformation and readily predicted using ab initio methods, affording critical information about the conformational distribution. The picture that emerges is that o-phenylenes fold into helices with offset stacking between every third repeat unit. In general, misfolding occurs primarily at the oligomer termini (i.e., "frayed ends"). Because of their structural simplicity, the folding can be described by straightforward models. The overall population can be divided into two enantiomeric pools, with racemization and misfolding as two distinct processes. Examination of substituent effects on folding reveals that the determinant of the relative stability of different conformers is (offset) aromatic stacking interactions parallel to the helical axis. That is, the folding of o-phenylenes is analogous to that of α-helices, with aromatic stacking in place of hydrogen bonding. The folding propensity can be tuned using well-known substituent effects on aromatic stacking, with moderate electron-withdrawing substituents giving nearly perfect folding. The combination of a simple folding mechanism and readily characterized conformational populations makes o-phenylenes attractive structural motifs for incorporation into more-complex architectures, an important part of the next phase of foldamer research.

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“…Rev. 2018, 118, 4731−4816 i v i d u a l n o t d i r e c t l y a s s o c i a t e d w i t h s c i t e i s p r o h i b i t e d .65b, left) 824. Furthermore, the oxidized form of poly28-S shows a weak CD signal because of the planarity of the structure and the intercalation of the dopant (ClO 4 −…”

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confidence: 99%

Conducting Polymers in the Fields of Energy, Environmental Remediation, and Chemical–Chiral Sensors

et al. 2018

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Conducting polymers (CPs), thanks to their unique properties, structures made on-demand, new composite mixtures, and possibility of deposit on a surface by chemical, physical, or electrochemical methodologies, have shown in the last years a renaissance and have been widely used in important fields of chemistry and materials science. Due to the extent of the literature on CPs, this review, after a concise introduction about the interrelationship between electrochemistry and conducting polymers, is focused exclusively on the following applications: energy (energy storage devices and solar cells), use in environmental remediation (anion and cation trapping, electrocatalytic reduction/oxidation of pollutants on CP based electrodes, and adsorption of pollutants) and finally electroanalysis as chemical sensors in solution, gas phase, and chiral molecules. This review is expected to be comprehensive, authoritative, and useful to the chemical community interested in CPs and their applications.

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Helical Sexithiophenes: An Experimental and Theoretical Study of Implicating the Alternating 2,2′:3,3′ Regioisomer as a Reliable Helical Motif.

Abstract: The syntheses of compounds 1a and 1b were reported previously, 6 and the synthesis of 1c is a simple modification (NCS exchanged for NBS; 60 ˚C) of the conversion of 1a to 1b. Crystal structures confirm structure and composition of 1a-c.

Cited by 3 publications

References 1 publication

Helical Poly(5-alkyl-2,3-thiophene)s: Controlled Synthesis and Structure Characterization

Helical Poly(5-alkyl-2,3-thiophene)s: Controlled Synthesis and Structure Characterization

Folding of ortho-Phenylenes

Conducting Polymers in the Fields of Energy, Environmental Remediation, and Chemical–Chiral Sensors

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