Oligothiophene wires: impact of torsional conformation on the electronic structure

Kislitsyn, Dmitry A.; Taber, Benjamen N.; Gervasi, Christian F.; Zhang, L.; Mannsfeld, Stefan C. B.; Prell, James S.; Briseño, Alejandro L.; Nazin, George V.

doi:10.1039/c5cp07092a

Cited by 12 publications

(8 citation statements)

References 66 publications

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“…Based on the crystal structure of 5,4′,3″,5‴-tetramethyl-2,2′:5′,2″:5″,2‴-quaterthiophene, the dihedral angle between the interior thiophene rings was found to be 19.8° even as a majority of the molecules were found to adopt the anti–anti–anti-orientation of the thiophene rings. , The adjacent outer and inner rings were found to be more coplanar, the dihedral angles between the mean planes being 2.1 and 5.3° for the two pairs. Different alkyl-substituted oligothiophenes displaying varied torsional conformations on the Au(111) surface were also previously studied, showing that cis–trans torsional disorder may not be a significant source of electronic disorder for oligothiophenes . In separate studies on the torsional motion about the central dihedral angles of oligothiophene, it was interestingly found that nonzero degrees of charge transport were predicted even at 90° twists and that the twisting potentials are highly dependent on chain length. , These studies provided a better understanding on the correlation of torsional flexibility of oligothiophenes and their resulting electronic properties.…”

Section: Introductionmentioning

confidence: 94%

“…Different alkyl-substituted oligothiophenes displaying varied torsional conformations on the Au(111) surface were also previously studied, showing that cis−trans torsional disorder may not be a significant source of electronic disorder for oligothiophenes. 12 In separate studies on the torsional motion about the central dihedral angles of oligothiophene, it was interestingly found that nonzero degrees of charge transport were predicted even at 90°twists and that the twisting potentials are highly dependent on chain length. 13,14 These studies provided a better understanding on the correlation of torsional flexibility of oligothiophenes and their resulting electronic properties.…”

Section: ■ Introductionmentioning

confidence: 99%

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Torsional Impacts on Quaterthiophene Segments Confined within Peptidic Nanostructures

et al. 2019

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The co-assembly behavior of peptide−π–peptide and peptide–alkyl–peptide triblock molecules that form one-dimensional (1D) nanostructures under acidic, aqueous environments is dependent on the peptide sequence and the torsional constraints imposed within the nanomaterial volume. Although a hydrophilic tripeptide sequence (Asp–Asp–Asp, DDD-) previously promoted isolation/dilution of minority π-electron components in the matrix of aliphatic peptides, a β-sheet promoting sequence (Asp–Val–Val, DVV-) led to blocks of the two components distributed within larger 1D self-assembled nanostructures. Furthermore, torsional restrictions exerted on the oligoaromatic π-electron unit by the self-assembly process can lead to changes in its conformation (for example, planarity), which has ramifications on its functionality within the peptide matrix. Here, we study this impact on thiophene-based π-electron units with inherently different geometries, viz., relatively planar 2,2′:5′,2″:5″,2‴-quaterthiophene and 3″,4′-dimethyl-2,2′:5′,2″:5″,2‴-quaterthiophene, which is twisted at the core bithiophene unit due to the presence of two methyl groups. These peptides were co-assembled at 5 and 20 mol % with peptide–n-decyl–peptide triblock molecules, and the resultant assemblies were studied using UV–vis absorption, photoluminescence, and circular dichroism spectroscopies. We found that torsional restriction in dimethylated quaterthiophene units can impact the stacking behavior of these 1D peptide nanoassemblies and have consequences on their photophysical properties. Additionally, these insights help in the understanding of the dependence of the optoelectronic properties of these materials on both the intrinsic conformation of π-units and the geometric constraints imposed by their immediate local environment under aqueous conditions.

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Section: Introductionmentioning

confidence: 94%

Section: ■ Introductionmentioning

confidence: 99%

Torsional Impacts on Quaterthiophene Segments Confined within Peptidic Nanostructures

et al. 2019

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“…The delocalized electronic system of polythiophene and oligo-thiophene enables conductance of this material [30][31][32]. The lowest unoccupied orbital of each of the thiophene rings couples electronically to its neighbors and forms a set of particlein-a-box-like states [33,34]. The LUMO to LUMO+1 level spacing of the quinquethiophene (5T) backbone is approx.…”

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confidence: 99%

“…The delocalized electronic system of polythiophene and oligothiophene enables conductance of this material [30,49,50]. The lowest unoccupied orbital of each of the thiophene rings couples electronically to its neighbors and forms a set of particle-ina-box-like states [51,52]. The lowest-energy unoccupied molecular orbital (LUMO) to LUMO þ 1 level spacing of the quinquethiophene (5T) backbone is approximately 0.7 eV [51], which is in good agreement with the energy difference calculated for free 5T based on DFT, as shown in Fig.…”

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confidence: 99%

Apparent Reversal of Molecular Orbitals Reveals Entanglement

Kocić

Repp

et al. 2017

Phys. Rev. Lett.

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The frontier orbital sequence of individual dicyanovinyl-substituted oligothiophene molecules is studied by means of scanning tunneling microscopy. On NaCl=Cuð111Þ, the molecules are neutral, and the two lowest unoccupied molecular states are observed in the expected order of increasing energy. On NaCl=Cuð311Þ, where the molecules are negatively charged, the sequence of two observed molecular orbitals is reversed, such that the one with one more nodal plane appears lower in energy. These experimental results, in open contradiction with a single-particle interpretation, are explained by a manybody theory predicting a strongly entangled doubly charged ground state. DOI: 10.1103/PhysRevLett.119.056801 For the use of single molecules as devices, engineering and control of their intrinsic electronic properties is all important. In this context, quantum effects such as electronic interference have recently shifted into the focus [1][2][3][4][5][6][7]. Most intriguing in this respect are electron correlation effects [8][9][10][11][12][13][14], which are intrinsically strong in molecules due to their small size [15][16][17][18][19].In general, Coulomb charging energies strongly depend on the localization of electrons and hence, on the spatial extent of the orbitals they occupy. Therefore, the orbital sequence of a given molecule can reverse upon electron attachment or removal if some of the frontier orbitals are strongly localized while others are not, like in, e.g., phthalocyanines [20][21][22][23][24]. Coulomb interaction may also lead to much more complex manifestations such as quantum entanglement of delocalized molecular orbitals.Here, we show that the energy spacing of the frontier orbitals in a single molecular wire of individual dicyanovinyl-substituted quinquethiophene (DCV5T) can be engineered to achieve near degeneracy of the two lowest-lying unoccupied molecular orbitals, leading to a strongly entangled ground state of DCV5T 2− . These orbitals are the lowest two of a set of particle-in-a-box-like states and differ only by one additional nodal plane across the center of the wire. Hence, according to the fundamental oscillation theorem of the Sturm-Liouville theory, their sequence has to be set with an increasing number of nodal planes, which is one of the basic principles of quantum mechanics [25,26]. This is evidenced and visualized from scanning tunneling microscopy (STM) and spectroscopy (STS) of DCV5T on ultrathin insulating films. Upon lowering the substrate's work function, the molecule becomes charged, leading to a reversal of the sequence of the two orbitals. The fundamental oscillation theorem seems strikingly violated since the state with one more nodal plane appears lower in energy. This contradiction can be solved, though, by considering intramolecular correlation leading to a strong entanglement in the ground state of DCV5T 2− . The experiments were carried out with a home-built combined STM and atomic force microscopy (AFM) using a qPlus sensor [27] operated in ultrahigh vacuum at a temperat...

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“…The STS measurements on 3T and 6T in a single molecular level reveal that the longer oligothiophene has the smaller HOMO–LUMO gap and that experimentally obtained HOMO–LUMO gaps are consistent with theoretically obtained ones. However, little is known about quaterthiophene (4T) and septithiophene (7T), which are composed of four and seven thiophene units, respectively (for the structural formulas, see Figure ), though alkyl-substituted 4T and 7T have been studied. , …”

Section: Introductionmentioning

confidence: 99%

Electronic Structures of Quaterthiophene and Septithiophene on Cu(111): Spatial Distribution of Adsorption-Induced States Studied by STM and DFT Calculation

et al. 2016

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The oligothiophene molecule family has a tunable energy gap between the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) as the function of the number of thiophene units. This tunability is of great use to controlling carrier injection at the molecule/electrode interface in molecule-based electronic devices. We investigate quaterthiophene (4T) and septithiophene (7T) molecules adsorbed on Cu(111) surfaces by scanning tunneling microscopy and spectroscopy (STM and STS) at room temperature. Both oligothiophene molecules form one-dimensional (1D) chain structures on Cu(111), and each molecule in the 1D structures is observed as a row of bright ovals corresponding to thiophene units. Observed features of 4T and 7T molecules differ from those expected from the HOMO and LUMO of the free-standing molecules, and density-functional calculations of a 4T molecule together with a Cu(111) surface reproduce the experimental STM images as they reflect characteristic spatial distribution of adsorption-induced states. In other words, the adsorption-induced states are spatially protruding out from the molecule and not completely localized in the space between the molecule and the Cu(111) surface.

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Oligothiophene wires: impact of torsional conformation on the electronic structure

Cited by 12 publications

References 66 publications

Torsional Impacts on Quaterthiophene Segments Confined within Peptidic Nanostructures

Torsional Impacts on Quaterthiophene Segments Confined within Peptidic Nanostructures

Apparent Reversal of Molecular Orbitals Reveals Entanglement

Electronic Structures of Quaterthiophene and Septithiophene on Cu(111): Spatial Distribution of Adsorption-Induced States Studied by STM and DFT Calculation

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