Oligo(<i>p</i>-phenyleneethynylene)s with Hydrogen-Bonded Coplanar Conformation

Hu, Wei; Zhu, Na; Tang, Wen; Zhao, Dahui

doi:10.1021/ol800753z

Cited by 68 publications

(74 citation statements)

References 37 publications

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“…Conformers with more coplanar arenes are better conjugated and exhibit higher conductivity and smaller band gaps. 54 Perpendicular orientation of adjacent arenes disrupts conjugation, lowers conductivity, and increases band gaps of OPE conformers. In B10, the OPE scaffold is deplanarized because intramolecular attraction between the weakly π-acidic, nonhalogenated NDIs fails to compensate charge repulsion between the side chains.…”

Section: Resultsmentioning

confidence: 99%

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

et al. 2009

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The photophysical properties of two hybrid multichromophoric systems consisting of an oligophenylethynyl (OPE) scaffold decorated by 10 red or blue naphthalene diimides (NDIs) have been investigated using femtosecond spectroscopy. Ultrafast charge separation was observed with both red and blue systems. However, the nature of the charge-separated state and its lifetime were found to differ substantially. For the red system, electron transfer occurs from the OPE scaffold to an NDI unit, independently of whether the OPE or an NDI is initially excited. However, charge separation upon OPE excitation is about 10 times faster, and takes place with a 100 fs time constant. The average lifetime of the ensuing charge-separated state amounts to about 650 ps. Charge separation in the blue system depends on which of the OPE scaffold or an NDI is excited. In the first case, an electron is transferred from the OPE to an NDI and the hole subsequently shifts to another NDI unit, whereas in the second case symmetry-breaking charge separation between two NDI units occurs. Although the charges are located on two NDIs in both cases, different recombination dynamics are observed. This is explained by the location of the ionic NDI moieties that depends on the charge separation pathway, hence on the excitation wavelength. The very different dynamics observed with red and blue systems can be accounted for by the oxidation potentials of the respective NDIs that are higher and lower than that of the OPE scaffold. Because of this, the relative energies of the two charge-separated states (hole on the OPE or an NDI) are inverted.

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Section: Resultsmentioning

confidence: 99%

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

et al. 2009

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“…OPE planarization was expected for the zipper architecture, and should give rise to higher charge mobility of the p-semiconductor. [27,28] Femtosecond fluorescence and transient absorption spectroscopy provided further support for the high photoactivity of OPEs ( Figure 4 a; Supporting Information, Figures S17-22). The appearance of OPE bleaching at 415 nm together with the broad NDI radical anion band around 600 nm indicated that, independent of the initially excited chromophore, very fast electron transfer takes place from OPE to NDI, and that the formed charge separated state (OPEC + -NDIC À pair) of 2 is relatively long-lived (flash photolysis lifetime t 4 = 270 ns; Supporting Information, Table S4).…”

mentioning

confidence: 81%

Topologically Matching Supramolecular n/p‐Heterojunction Architectures

et al. 2009

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“…In the previous study, [18] we showed that the effective conjugation length of the oligomers was extended by restraining the rotational motion of the phenylene units in the OPE backbone and confining them into a co-planar conformation by virtue of intramolecular hydrogen bonds. This was evidenced by a bathochromic shift of the absorption band, relative to that of analogous OPEs without such intramolecular hydrogen bonds.…”

Section: H Nmr Study Of Key Monomersmentioning

confidence: 97%

“…1 a 402 (2.6) [b] 1 b 456 (7.1) [b] 1 c 471 (11) [b] (11) [a] The precision of the extinction coefficient (e) was approximately AE 15 %. [b] Taken from reference [18].…”

Section: H Nmr Study Of Key Monomersmentioning

confidence: 99%

“…[17] Previously, we synthesised a series of OPEs in which intramolecular hydrogen bonds were implemented between neighbouring phenylene pairs in the backbone (1 a-c, Scheme 1). [18] The hydrogenbond donors were the NH protons of the alkanamido groups, and the acceptors were the ester carbonyl oxygen atoms on every other phenylA C H T U N G T R E N N U N G (ene) unit. Upon formation of the intramolecular hydrogen bonds, all of the phenylA C H T U N G T R E N N U N G (ene) rings in the backbone were constrained in a co-planar conformation.…”

Section: Introductionmentioning

confidence: 99%

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Oligo(p‐phenylene‐ethynylene)s with Backbone Conformation Controlled by Competitive Intramolecular Hydrogen Bonds

Yan

Zhao

2011

Chemistry A European J

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A series of conjugated oligo(p-phenylene-ethynylene) (OPE) molecules with backbone conformations (that is, the relative orientations of the contained phenylene units) controlled by competitive intramolecular hydrogen bonds to be either co-planar or random were synthesised and studied. In these oligomers, carboxylate and amido substituents were attached to alternate phenylene units in the OPE backbone. These functional groups were able to form intramolecular hydrogen bonds between neighbouring phenylene units. Thereby, all phenylene units in the backbone were confined in a co-planar conformation. This planarised structure featured a more extended effective conjugation length than that of regular OPEs with phenylene units adopting random orientation due to a low rotational-energy barrier. However, if a tri(ethylene glycol) (Tg) side chain was appended to the amido group, it enabled another type of intramolecular hydrogen bond, formed by the Tg chain folding back and the contained ether oxygen atom competing with the ester carbonyl group as the hydrogen-bond acceptor. The outcome of this competition was proven to depend on the length of the alkylene linker joining the ether oxygen atom to the amido group. Specifically, if the Tg chain folded back to form a five-membered cyclic structure, this hydrogen-bonding motif was sufficiently robust to overrule the hydrogen bonds between adjacent phenylene units. Consequently, the oligomers assumed non-planar conformations. However, if the side chain formed a six-membered ring by hydrogen bonding with the amido NH group, such a motif was much less stable and yielded in the competition with the ester carbonyl group from the adjacent phenylene unit. Thus, the hydrogen bonds between the phenylene units remained, and the co-planar conformation was manifested. In our system, the hydrogen bonds formed by the back-folded Tg chain and amido NH group relied on a single oxygen atom as the hydrogen-bond acceptor. The additional oxygen atoms in the Tg chain made a negligible contribution. A bifurcated hydrogen-bond motif was unimportant. From our results, in combination with the results from an independent study by Meijer et al., it is evident that intramolecular hydrogen bonds involving back-folded oligo(ethylene glycol) moieties may differ in their structural details. Absorption spectroscopy served as a convenient yet sensitive technique for analysing hydrogen-bonding motifs in our study.

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Oligo(p-phenyleneethynylene)s with Hydrogen-Bonded Coplanar Conformation

Cited by 68 publications

References 37 publications

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

Topologically Matching Supramolecular n/p‐Heterojunction Architectures

Oligo(p‐phenylene‐ethynylene)s with Backbone Conformation Controlled by Competitive Intramolecular Hydrogen Bonds

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