Charge–transfer organic crystals: Molecular vibrations and spectroscopic effects of electron–molecular vibration coupling of the strong electron acceptor TCNQF4

Meneghetti, Moreno; Pecile, Cesare

doi:10.1063/1.450086

Cited by 142 publications

(165 citation statements)

References 59 publications

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“…Note that the alkyl chains are omitted for clarity. The electronic states of the TTF units and F 4 -TCNQ molecules in the nanowire, as well as the (2)(F 4 -TCNQ) 2 crystal, are in a fully charged transferred state, as seen by comparing the IR spectra with that of a reported complex (33) and (1a)(F 4 -TCNQ) 2 (34).…”

Section: Resultsmentioning

confidence: 93%

Formation of oriented molecular nanowires on mica surface

Akutagawa

Ohta

Hasegawa

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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Molecular ''nanowire'' structures composed of the charge transfer complex of a bis-tetrathiafulvalene substituted macrocycle and tetrafluorotetracyanoquinodimethane were constructed on mica substrates by employing the Langmuir-Blodgett technique. The nanowires transferred from a dilute aqueous potassium chloride subphase had typical dimensions of 2.5 nm ؋ 50 nm ؋ 1 m. The nanowires are oriented to specific directions, corresponding to the directions of the potassium-ion array on the mica surface having sixfold symmetry. Such correlation between the nanowires and the substrate surface was also observed when a dilute aqueous rubidium chloride subphase was used. On the other hand, the correlation completely disappeared when the subphase contained divalent cations, indicating that the molecular nanowires orient by recognizing the monocation array on the mica surface. The nanowires formed by the vertical dipping method coexist with the monolayers. Only nanowire structures are, however, observed when we apply the horizontal lifting method. Based on the crystal structure of a related complex, a possible structure of the nanowires is presented. The conductivity of the nanowires was estimated to be of the order of 10 ؊3 S⅐cm ؊1 . The nanowires formed specific (regular) structures such as T-shape junctions, suggesting their use in construction of future molecular nanoscale devices.

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Section: Resultsmentioning

confidence: 93%

Formation of oriented molecular nanowires on mica surface

Akutagawa

Ohta

Hasegawa

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

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“…The vibrational bands in the 2,800-3,000 cm À 1 region originate from the alkyl side chains of the polymers. F4-TCNQ vibrations, either in neutral or charged state 51 , are not apparent due to the low dopant concentrations.…”

Section: Discussionmentioning

confidence: 99%

How intermolecular geometrical disorder affects the molecular doping of donor–acceptor copolymers

et al. 2015

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Molecular doping of conjugated polymers represents an important strategy for improving organic electronic devices. However, the widely reported low efficiency of doping remains a crucial limitation to obtain high performance. Here we investigate how charge transfer between dopant and donor-acceptor copolymers is affected by the spatial arrangement of the dopant molecule with respect to the copolymer repeat unit. We p-dope a donor-acceptor copolymer and probe its charge-sensitive molecular vibrations in films by infrared spectroscopy. We find that, compared with a related homopolymer, a four times higher dopant/ polymer molar ratio is needed to observe signatures of charges. By DFT methods, we simulate the vibrational spectra, moving the dopant along the copolymer backbone and finding that efficient charge transfer occurs only when the dopant is close to the donor moiety. Our results show that the donor-acceptor structure poses an obstacle to efficient doping, with the acceptor moiety being inactive for p-type doping.

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“…Iwasa et al used the TCNQ b 1u ν 19 CN stretching frequency to estimate ρ, obtaining a change from 0.59 to 0.69 at the transition [46]. However, it is well known that the CN stretching frequency gives unreliable (generally overestimated) values of ρ since it suffers from uncertainty about the correct assignment, and is subject to extrinsic effects due to the interactions with the surrounding molecules [48]. For this reason, Castagnetti et al used the well tested charge sensitive TCNQ b 1u ν 20 C=C stretching, that in TMB-TCNQ moves from 1532 to 1528 cm −1 , corresponding to a ρ increase from 0.29 to 0.41 [19].…”

Section: Tmb-tcnqmentioning

confidence: 99%

Phenomenology of the Neutral-Ionic Valence Instability in Mixed Stack Charge-Transfer Crystals

2017

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Organic charge-transfer (CT) crystals constitute an important class of functional materials, characterized by the directional charge-transfer interaction between π-electron Donor (D) and Acceptor (A) molecules, with the formation of one-dimensional ...DADAD... stacks. Among the many different and often unique phenomena displayed by this class of crystals, Neutral-Ionic phase transition (NIT) occupies a special place, as it implies a collective electron transfer along the stack. The analysis of such a complex yet fascinating phenomenon has required many years of investigation, and still presents some open questions and challenges. We present an updated and extensive summary of the phenomenology of the temperature induced NIT, with emphasis on the spectroscopic signatures of the transition. A much shorter summary is given for the NIT induced by pressure. Finally, we report on the exploration, by chemical substitution, of the phase space of ...DADAD... CT crystals, aimed at finding materials with important semiconducting or ferroelectric properties, and at understanding the subtle factors determining the crystal packing.

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Charge–transfer organic crystals: Molecular vibrations and spectroscopic effects of electron–molecular vibration coupling of the strong electron acceptor TCNQF4

Cited by 142 publications

References 59 publications

Formation of oriented molecular nanowires on mica surface

Formation of oriented molecular nanowires on mica surface

How intermolecular geometrical disorder affects the molecular doping of donor–acceptor copolymers

Phenomenology of the Neutral-Ionic Valence Instability in Mixed Stack Charge-Transfer Crystals

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