A simple interpretation of the vibrational spectra of undoped, doped and photoexcited polyacetylene: Amplitude mode theory in the GF formalism

Castiglioni, Chiara; Navarrete, Juan T. López; Zerbi, G.; Gussoni, M.

doi:10.1016/0038-1098(88)90352-3

Cited by 235 publications

(160 citation statements)

References 13 publications

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“…[27][28][29] As will be shown in the following, the 1.1 THz resonance in pentacene corresponds to nuclear modes that strongly modulate intermolecular electron transfer, i.e., the modes with the largest off-diagonal electron phonon coupling. These are the same modes that limit the charge mobility according to the TO model.…”

Section: ͑1͒mentioning

confidence: 86%

On the mechanism of charge transport in pentacene

Laarhoven

Flipse

Koeberg³

et al. 2008

The Journal of Chemical Physics

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Terahertz transient conductivity measurements are performed on pentacene single crystals, which directly demonstrate a strong coupling of charge carriers to low frequency molecular motions with energies centered around 1.1 THz. We present evidence that the strong coupling to low frequency motions is the factor limiting the conductivity in these organic semiconductors. Our observations explain the apparent paradox of the "bandlike" temperature dependence of the conductivity beyond the validity limit of the band model. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2955462͔Recent years have seen much interest in the conductivity of pentacene and other molecular semiconductors of the oligoacene family, fueled by the unique properties of these materials. Oligoacenes are flexible, cheap, and exhibit relatively high charge carrier mobilities, 1 allowing for novel applications in electronic devices. [2][3][4] Despite this interest, the nature of charge transport in the materials has remained the subject of intense debate.Crystalline organic semiconductors exhibit charge mobilities that decrease with temperature. [5][6][7][8][9] In analogy to inorganic semiconductors, this has been interpreted as an indication of delocalized charge carriers and a "bandlike" transport mechanism. 10-13 Theoretical models based on polaronic band conduction 14 indeed provide a good qualitative description of the bandlike mobility of charge carriers in pentacene, but the factors determining the absolute charge mobility remain unknown. For instance, an analysis of the high temperature mobility has indicated that the mean free path of charge carriers is of the same magnitude as the intermolecular distance. 15 It is not clear as to why the signature of delocalized bandlike transport persists at these temperatures, where the mean free path is smaller than the intermolecular distances. Because of the "softness" of these van der Waals bonded organic crystals, it is possible that the coupling of the carriers with the intermolecular vibrations could play a key role in the description of the charge carrier dynamics. Troisi and Orlandi 16 have recently formulated a model ͑TO model͒ that states that the charge mobility in oligoacenes is limited by large fluctuations of the electronic coupling between adjacent organic molecules due to thermal molecular motions, in particular, the low energetic phonon modes with energies around 1 THz. 17 This model correctly describes the bandlike temperature dependence of the mobility, including its absolute value, outside the validity of delocalized transport models. 16 Direct experimental evidence for the various proposed models has been lacking. In particular, experimental insights into the role of intermolecular low frequency vibrational modes in determining the charge transport mechanism have been missing to date.Terahertz spectroscopy 18 provides the opportunity of studying the response of charge carriers in the frequency range of these modes, and has proven useful for investigating photocarrier dynamics in...

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Section: ͑1͒mentioning

confidence: 86%

On the mechanism of charge transport in pentacene

Laarhoven

Flipse

Koeberg³

et al. 2008

The Journal of Chemical Physics

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“…[66][67][68][69][70] In this field, Raman spectroscopy certainly plays a major role (see for instance ref. [71][72][73][74][75] and references therein).…”

Section: The Ideal Infinite Wire: Interplay Between Electronic and VImentioning

confidence: 99%

“…For instance, it has been verified that the sequence of the interaction stretching force constants involving a given CC bond and a sequence of bonds along a path made by consecutive CC bonds has alternate signs in polyynes, 55,62,73 similarly to polyenes and graphene. 52,[67][68][69]74 As a consequence, the sum in eqn (2) has a negative value. This provides a π-conjugationdependent contribution that lowers the phonon frequency with respect to the value given by the diagonal force constants k 1 , k 2 .…”

Section: The Ideal Infinite Wire: Interplay Between Electronic and VImentioning

confidence: 99%

Carbon-atom wires: 1-D systems with tunable properties

et al. 2016

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This review provides a discussion of the current state of research on linear carbon structures and related materials based on sp-hybridization of carbon atoms ( polyynes and cumulenes). We show that such systems have widely tunable properties and thus represent an intriguing and mostly unexplored field for both fundamental and applied sciences. We discuss the rich interplay between the structural, vibrational, and electronic properties focusing on recent advances and the future perspectives of carbon-atom wires and novel hybrid sp-sp 2 -carbon architectures.

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“…Politiofeno 51 , poli-p-fenileno 52 , polipirrol 53 , polifurano 54 e polip-fenilenovinileno (PPV) 55 são alguns dos polímeros conjugados que tiveram seus espectros Raman interpretados utilizando o ECCM, além do poliacetileno 29,46 . Zerbi et al 18 mostraram que diferentes polímeros conjugados formados por anéis aromáticos apresentam diferentes valores de dispersão Raman e que esta diferença se deve, principalmente, ao grau de confinamento que os elétrons π experimentam dentro do anel aromático.…”

Section: Figura 7 Espectro Eletrônico Do O Poli(iodeto De 2-n-t-butiunclassified

“…No 29,30 constrói uma coordenada de conjugação efetiva (Q ß ) a qual descreve a variação das distâncias das ligações C=C e C-C quando a molécula passa do estado fundamental para o estado excitado. Estes modelos serão discutidos mais amplamente a seguir.…”

Section: Introductionunclassified

Modelos para dispersão Raman em polímeros conjugados

Millen¹,

Faria²,

Temperini³

2005

Quím. Nova

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Recebido em 12/4/04; aceito em 2/9/04; publicado na web em 5/11/04 RAMAN DISPERSION MODELS IN CONJUGATED POLYMERS. Raman dispersion refers to the dependence of the position of Raman bands on the energy of the exciting radiation. In this work, the three main models currently used to explain this phenomenon (Conjugated Length Model, Amplitude Mode Model and Effective Conjugation Coordinate Model) are discussed. Raman dispersion is a consequence of π electron delocalization, but each model describes in a different way how π electron delocalization affects the position of Raman bands. Here the features, qualities and problems of the three models are highlighted.Keywords: vibrational spectroscopy; conjugated polymers; Raman dispersion. INTRODUÇÃOA espectroscopia Raman teve origem em 1928 quando C.V. Raman publicou um artigo onde descrevia a observação experimental do espalhamento inelástico da luz visível 1 , feito este que lhe rendeu o prêmio Nobel de Física em 1930 2 . Assim como a espectroscopia de absorção (ou emissão) no infravermelho, a espectroscopia Raman fornece informações sobre níveis de energia vibracionais e sobre a estrutura molecular. Como os processos físicos envolvidos em cada uma dessas duas técnicas são diferentes, com regras de seleção diferentes, as informações fornecidas por elas não são as mesmas, mas complementares 3 .A energia da radiação inelasticamente espalhada pode ser maior ou menor que a energia incidente (espalhamento anti-Stokes e Stokes, respectivamente) e essa diferença é igual à transição vibracional da molécula. Caso as energias incidente e espalhada tenham os mesmos valores, o espalhamento será elástico (também chamado de espalhamento Rayleigh) e nenhuma informação vibracional molecular estará nele contida. Comumente, o espalhamento Stokes é o mais utilizado pela maior intensidade de seu sinal em relação ao espalhamento anti-Stokes, pois enquanto o primeiro depende da população do estado vibracional fundamental, o último depende da população de estados vibracionais excitados 4 . Esquematicamente podemos representar o espalhamento inelástico e elástico como apresentado na Figura 1.Se a energia da radiação excitante coincidir ou se aproximar da energia de uma transição eletrônica permitida da molécula há a intensificação do sinal espalhado. Esta intensificação, porém, é seletiva e não tem a mesma magnitude para todas as bandas, podendo este ganho de intensidade chegar a cinco ordens de grandeza 5 . Este tipo de intensificação é chamado de efeito Raman ressonante.A intensidade das bandas Raman, no efeito Raman ressonante, foi descrita por Albrecht 6 como a soma de quatro termos, denominados A, B, C e D. Destes, o mais importante na grande maioria dos casos é o termo A, o qual é responsável pela intensificação dos modos totalmente simétricos, enquanto o termo B responde pelo aumento na intensidade dos modos não-totalmente simétricos que intermediam o acoplamento entre o primeiro e o segundo estados eletrônicos excitados (acoplamento vibrônico). O termo C está relacionado com o acopla...

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A simple interpretation of the vibrational spectra of undoped, doped and photoexcited polyacetylene: Amplitude mode theory in the GF formalism

Cited by 235 publications

References 13 publications

On the mechanism of charge transport in pentacene

On the mechanism of charge transport in pentacene

Carbon-atom wires: 1-D systems with tunable properties

Modelos para dispersão Raman em polímeros conjugados

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