Fine Tuning of the Electronic Properties of Linear π‐Conjugated Oligomers by Covalent Bridging

Blanchard, Philippe; Verlhac, Patrick; Michaux, Laurent; Frère, Pierre; Roncali, Jean

doi:10.1002/chem.200500853

Cited by 34 publications

(24 citation statements)

References 58 publications

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“…As expected, covalent rigidification of the precursor produces a significant reduction of the band gap of the corresponding polymer; however, the magnitude of this reduction is limited by the remaining possible inter‐ring rotations in the conjugated backbone. More recent work has shown that covalent rigidification is also effective for reducing the gap of extended oligo(thienylene vinylene)s 23. To summarize, covalent rigidification of π‐conjugated systems represents an efficient strategy for band gap control.…”

Section: Synthetic Principles For Band‐gap Engineering “The Tool Box”mentioning

confidence: 99%

Molecular Engineering of the Band Gap of π‐Conjugated Systems: Facing Technological Applications

Roncali

2007

Macromol. Rapid Commun.

668

538

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IntroductionThe control of the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap of p-conjugated systems and hence of the band gap of the corresponding materials has been in the centre of the synthetic chemistry of functional p-conjugated systems for more than twenty years. Following the discovery of the metallic conductivity of doped polyacetylene, [1] conjugated polymers derived from heteroaromatic units such as polypyrrole [2] or polythiophene (PT) [3] emerged in the early eighties as an answer to the problems posed by the lack of stability of polyacetylene in atmospheric conditions. Owing to a unique combination of environmental stability, conductivity, moderate band gap and structural versatility, thiophenebased p-conjugated systems have progressively supplanted other classes of systems in both fundamental and technologically-oriented research.[4]Whereas band gap control has been a target already at an early stage of research on conjugated polymers, during the past two decades the field has undergone major changes in both its finalities and synthetic approaches. During the 1980-1990 period conducting polymers were essentially considered as possible alternatives for metals or metal oxides in bulk applications such as electrode Feature ArticleFor almost two decades, the search of an intrinsically-conductive organic metal has represented the major driving force for research on control of the band gap of extended p-conjugated systems. However, the emergence of the application of p-conjugated oligomers and polymers in field-effect transistors, light-emitting diodes, electrochromic devices and solar cells has introduced major changes in the chemistry of gap engineering. Besides controlled band gap, active materials for electronic and photonic applications must present appropriate absorption and/or emission properties, highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) energy levels and charge-transport properties. The aim of this short review is to present an overview of the recent trends in this area in order to identify possible directions for future research. Consequently, while considerable research effort was invested in the optimization of the conductivity of doped conjugated polymers, the search for a zero-band-gap polymer capable of forming an intrinsically conductive material, namely a true organic metal, represented the ''Holy Grail'' for the chemistry of conjugated systems.[5]The turn of the nineties has been marked by a progressive decline of research on the bulk applications of conducting polymers, with the parallel emergence of research focused on the applications of conjugated systems in electronic and photonic devices such as field-effect transistors (FETs), light-emitting diodes (LEDs) and solar cells. [6][7][8] These applications, based on the electronic properties of the neutral semiconducting form of conjugated systems, have had a profound impact on the chemistry of these systems by providing new finalities. This new situation ...

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Section: Synthetic Principles For Band‐gap Engineering “The Tool Box”mentioning

confidence: 99%

Molecular Engineering of the Band Gap of π‐Conjugated Systems: Facing Technological Applications

Roncali

2007

Macromol. Rapid Commun.

668

538

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“…Several publications have shown that the hybrid functional B3LYP is adequate for studying the electronic structures of π-conjugated systems such as those involving a phosphole moiety, [34] EDOT [35] or π-conjugated oligomers. [36] Second derivatives were calculated in order to check that the optimised structures are true minima on the potential energy surface. All total energies have been zero-point-energy (ZPE) and temperature-corrected using unscaled density functional frequencies.…”

Section: Theoretical Sectionmentioning

confidence: 99%

How to Build Fully π‐Conjugated Architectures with Thienylene and Phenylene Fragments

et al. 2007

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A series of small-sized model π-conjugated oligomers have been prepared from thienylene and phenylene or dimethylor dimethoxy-substituted phenylene units. Crystallographic data for the methoxylated compound show a quasi-planar conformation with a non-covalent S-O interaction. The resulting strong conjugation in the gas phase has also been highlighted by UV/photoelectron spectroscopy and theoretical calculations (DFT). Indeed, for these compounds there is a large energy gap ∆E π arising from the interaction between the molecular orbitals of the isolated thienylene-phenylene species. This can be explained in terms of the energies of the two π orbitals of the dimethoxyphenylene unit, the shape of these molecular orbitals in a three-orbital interaction diagram and by the presence of the S···O interaction which re-

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“…It is known that the highest occupied molecular orbitallowest unoccupied molecular orbital (HOMO-LUMO) energy gap of π-conjugated systems containing heteroaromatic units depends on various structural factors such as bond length alternation, planarity, aromatic resonance energy, and electronic effects promoted by side chain substituents. 8 In the present study, the spectral and photophysical properties of three of these alternating copolymers were investigated in solution (room and low temperature) and in the solid state (thin films). With one of the copolymers, samples of two different molecular weights and polydispersities were studied to see whether this has any effects on either photophysical or film-forming properties.…”

Section: Introductionmentioning

confidence: 99%

Spectral and Photophysical Studies of Poly[2,6-(1,5-dioctylnaphthalene)]thiophenes

et al. 2007

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A complete spectroscopic and photophysical study of three alternating naphthalene-R-thiophene copolymers was undertaken in solution (room and low temperature) and in the solid state (thin films in a Zeonex matrix). The study comprises absorption, emission, and triplet-triplet spectra together with quantitative measurements of quantum yield (fluorescence, intersystem-crossing, internal conversion, and singlet oxygen formation) lifetimes and singlet and triplet energies. The overall data allow the determination of the rate constants for all the decay processes. Comparison between the behavior of analogous 1-naphthyl(oligo)thiophenes and the 2,6-naphthalene(oligo)thiophene copolymers allows several important observations. First, the polymers display higher fluorescence quantum yields and lower S 1 ∼∼fT 1 intersystem-crossing yields than the oligomers. This can be attributed to the presence of the 1,5-dioctyloxynaphthalene groups in the copolymers leading to a more rigid polymer backbone, which decreases radiationless deactivation and increases the radiative efficiency. Second, the singlet and triplet energies are significantly lower in the polymers than with the corresponding oligomers. This implies a lower HOMO-LUMO energy difference in the polymers due to an extended π-delocalization. Third, the singlet-to-triplet (S 1-T 1) energy splitting is higher in the oligomers than with the polymers, even though the former display higher intersystem-crossing yields. It is suggested that this may result from intersystem-crossing in the oligomers involving significant charge-transfer (CT) character (spinorbit coupling is mediated by CT mixing involving the singlet and triplet states in matrix elements of the type 〈 1 Ψ CT |H′| 3 Ψ 1 〉) of the relevant excited states but that is less important with the polymers. We believe that this may be relevant to understanding the nature of CT states in conjugated copolymers.

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Fine Tuning of the Electronic Properties of Linear π‐Conjugated Oligomers by Covalent Bridging

Cited by 34 publications

References 58 publications

Molecular Engineering of the Band Gap of π‐Conjugated Systems: Facing Technological Applications

Molecular Engineering of the Band Gap of π‐Conjugated Systems: Facing Technological Applications

How to Build Fully π‐Conjugated Architectures with Thienylene and Phenylene Fragments

Spectral and Photophysical Studies of Poly[2,6-(1,5-dioctylnaphthalene)]thiophenes

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