Temperature-dependent photoluminescence of organic semiconductors with varying backbone conformation

Guha, S.; Rice, J. D.; Yau, Y. T.; Martin, C. M.; Chandrasekhar, M.; Chandrasekhar, H. R.; Guentner, R.; Freitas, P. Scanduicci de; Scherf, Ullrich

doi:10.1103/physrevb.67.125204

Cited by 139 publications

(120 citation statements)

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“…Upon increasing the temperature, the singlet excitons typically become more localized in smaller conjugated chain segments. 10 This localization results in a higher value for S with increasing temperatures. The red-shift of the PL spectra upon increasing pressures is a clear sign of an enhanced effective conjugation and thus represents a higher delocalization of the excited state.…”

Section: A Discussion Of Pl Resultsmentioning

confidence: 97%

Tuning Intermolecular Interactions in Dioctyl-Substituted Polyfluorene via Hydrostatic Pressure

et al. 2010

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Polyfluorenes (PFs) represent a unique class of poly para-phenylene based blue-emitting polymers with intriguing structure-property relationships. Slight variations in the choice of functionalizing side chains result in dramatic differences in the inter-and intra-chain structures in PFs. We present photoluminescence (PL) and Raman scattering studies of bulk samples and thin films of dioctylsubstituted PF (PF8) under hydrostatic pressure. The bulk sample was further thermally annealed at 1.9 GPa. The PL vibronics of the as-is sample red-shift at an average rate of 26 meV/GPa.The thermally annealed sample is characterized by at least two phase transitions at 1.1 GPa and 4.2 GPa, each of which has a different pressure coefficient for PL vibronics. The Huang-Rhys factor, a measure of the electron-phonon interaction, is found to increase with increasing pressures signaling a higher geometric relaxation of the electronic states. The Raman peaks harden with increasing pressures; the intra-ring C-C stretch frequency at 1600 cm −1 has a pressure coefficient of 7.2 cm −1 /GPa and exhibits asymmetric line shapes at higher pressures, characteristic of a strong electron-phonon interaction. The optical properties of PF8 under high pressure are further contrasted with those of a branched side chain substituted PF.

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Section: A Discussion Of Pl Resultsmentioning

confidence: 97%

Tuning Intermolecular Interactions in Dioctyl-Substituted Polyfluorene via Hydrostatic Pressure

et al. 2010

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“…For this new configuration, the tunneling is much slower, but as it requires less energy to be reached, it is associated with lower activation energy. We have not been able to find direct measurements of the phonon temperature associated with the charge transport, but the one associated with exciton emission in conjugated polymers is in the range of 300-500 K. [8,9] Namely, in most temperaturedependent measurements this effect will be highly influential, and may mask the effects that are dominant in hard materials. We will come back to the issue of polaronic transfer rate in the context of nonequilibrium transport further ahead in this paper.…”

Section: Reviewmentioning

confidence: 98%

Charge Transport in Disordered Organic Materials and Its Relevance to Thin‐Film Devices: A Tutorial Review

et al. 2009

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In this review, we describe a variety of models or theoretical approaches to transport in disordered media and discuss the implication to modern organic devices. There are far too many models or variations, so our aim is not to try to cover them all. Instead, we show that when the different models are presented along with the assumptions included while being developed, they can all teach us and help us to develop some intuition regarding what goes on in nonordered materials. One may encounter debates regarding a model being wrong, but it is our belief that only when the models are used out of context (not within their basic assumptions) the obtained results could be false.One of the things one encounters while starting to study organic semiconductors is that the textbook models taught in semiconductor-device courses have to be revisited, and one has to look for ''old'' books that were written before silicon technology took over. With this spirit, we start a few years back, or a century ago. In 1900, three years after the discovery of the electron by Thomson, Drude proposed a model that explained the known conductivity phenomenon in metals and other types of materials.[1] This model was based on the assumption that electrons classically accelerate under an applied electric field and collide with the lattice's heavy positive ions. Upon collision, the electrons were assumed to scatter into a random angle and at a speed that was on average consistent with the local temperature. It would then go on accelerating until the next scattering event. This model, although erroneous in the assumption that the basic scattering centers were the lattice ions, was able to physically explain the already known Ohm's law and the Joule heating effect. Along with the debut of quantum mechanics came the quantum mechanical description of matter and the realization that in a well-ordered lattice electrons should be mathematically described as Bloch waves, and that the scattering was not the result of collisions with any lattice ion but rather scattering from defects, contaminations, and phonons. Nevertheless, the Drude model, under the semiclassical approximation, is conceptually appropriate for describing electron transport through crystal lattices, that is, freely roaming charge carriers that scatter upon collisions with defects, contaminations, and phonons. The carriers earn the name ''free'' whenever the material properties are such that the mean free path between collisions, L, is much longer than the typical carrier's Bloch wavelength, thus the carriers have very broad wavefunctions extending over many lattice units.However, as was historically elucidated by Anderson, [2] introducing disorder into the lattice and breaking the crystal symmetry results in the wavefunctions becoming localized and in the formation of energy states in the forbidden band-gap. The Drude concepts, and others deriving on its intuitive approach, can no longer serve us in explaining transport under such circumstances. Since the materials we are interested in a...

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“…Utilizando-se os valores das intensidades das bandas e o nú-mero de onda obtido através do espectro vibracional, pode-se obter o parâmetro de Huang-Rhys (S) e a energia de relaxação de decaimento eletrônico (E Rel ), através da Equação 1 [102][103][104]109,110 . Quando polímeros conjugados são utilizados, além dos estados eletrônicos envolvidos, existem outras variáveis que controlam a região espectral e o perfil da banda.…”

Section: Propriedades Fotofísicas Dos Polímeros Eletroluminescentesunclassified

Dispositivos poliméricos eletroluminescentes

Oliveira¹,

Cossiello²,

Atvars³

et al. 2006

Quím. Nova

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Recebido em 29/9/04; aceito em 21/6/05; publicado na web em 1/12/05 POLYMERIC LIGHT EMITTING DEVICES. Here we present an overview of electroluminescent devices that use conjugated polymers as the active media. The principal components of the devices are described and we show some examples of conjugated polymers and copolymers usually employed in polymeric light emitting devices (PLED). Some aspects of the photo and electroluminescence properties as well as of the energy transfer processes are discussed. As an example, we present some of the photophysical properties of poly(fluorene)s, a class of conjugated polymers with blue emission.Keywords: polymer; photoluminescence; electroluminescence. INTRODUÇÃOOs primeiros trabalhos sobre condução eletrônica em polímeros conjugados datam de 1970 1,2 sendo que a eletroluminescência (EL) em polímeros foi relatada pela primeira vez em 1989 3 . O uso de polímeros conjugados com um sistema de elétrons π delocalizados em dispositivos optoeletrônicos, conhecidos como OPLEDs ("Organic Polymeric Light Emission Devices"), tem crescido desde então. Na atualidade, monitores coloridos na forma de matriz ativa, fabricados com polímeros orgânicos emissores de luz (OPLEDs) estão na fronteira de serem comercializados. As razões para o sucesso dos OPLEDs devem-se às múltiplas possibilidades de estruturas químicas dos compostos possíveis, às várias possibilidades de formas de montagem dos dispositivos, aliadas à alta performance e ao menor custo de produção 4 . A tecnologia de exibição não é, entretanto, o único campo em que materiais orgânicos em geral, e poliméricos conjugados em particular, aparecem com um futuro promissor. Entre esses novos campos aparecem as novas tecnologias de células solares 5-8 , transistores 9-11 , emissores tipo laser, sistemas de armazenamento e circuitos integrados poliméricos [12][13][14][15][16][17] . O uso de materiais orgânicos, poliméricos ou não, nos vários tipos de dispositivos tem, entre suas principais vantagens, a imensa possibilidade de preparação de estruturas químicas diferentes, além de poderem ser misturados, formando sistemas com outras propriedades. Têm, entretanto, alguns problemas tecnológicos importantes ainda não resolvidos, relacionados com a menor estabilidade química quando comparados com materiais inorgânicos ou organo-metálicos. Entretanto, a possibilidade de mistura física entre componentes permitindo a obtenção de sistemas com diferentes propriedades é, sem dúvida, uma forma atraente e de custo reduzido de preparação de novos materiais. Essa flexibilidade nas formas de preparação de sistemas é particularmente interessante no caso de polímeros eletroluminescentes para os quais pequenas alterações nas rotas de síntese podem levar a materiais com diferentes estruturas e, o fato de apresentarem diferentes estruturas químicas, leva a que os materiais passem a emitir em diferentes regiões do espectro [18][19][20][21] . As diferenças nos processos sintéticos podem, também, envolver reações de copolimerização, permitindo a geração de materi...

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Temperature-dependent photoluminescence of organic semiconductors with varying backbone conformation

Cited by 139 publications

References 36 publications

Tuning Intermolecular Interactions in Dioctyl-Substituted Polyfluorene via Hydrostatic Pressure

Tuning Intermolecular Interactions in Dioctyl-Substituted Polyfluorene via Hydrostatic Pressure

Charge Transport in Disordered Organic Materials and Its Relevance to Thin‐Film Devices: A Tutorial Review

Dispositivos poliméricos eletroluminescentes

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