“…Miller et al13a found that high-molecular weight fluorene copolymers may not exhibit any emission at longer wavelengths. The photoluminescent quantum yields of PSiloBg1 and PSiloBg3, which are listed in Table , are similar to those of PDHF . The PL quantum yields of PSiloBg1 and PSiloBg3 in solution were 0.83 and 0.86, respectively …”
Section: Resultsmentioning
confidence: 53%
“…The copolymers exhibited good thermal stability. As shown in Figure , the decomposition temperatures for 5% weight loss ( T d ) of the copolymers were above 420 °C, and the copolymers exhibited no significant weight loss upon being heated to ∼400 °C (see Table for T d values). 4 TGA traces and DSC thermograms of the polymers.…”
Section: Resultsmentioning
confidence: 98%
“…Subsequent work has established polyfluorenes as promising candidates for applications requiring blue light-emitting materials. Polyfluorenes have many properties that favor their use over other conjugated polymers in blue light-emitting applications. ,− They exhibit high photoluminescence (PL) and electroluminescence efficiencies, offer facile functionalization at the C-9 position of fluorene, and have good solubility in common organic solvents such as chloroform, toluene, and tetrahydrofuran (THF). − …”
The first novel polyfluorene copolymers containing siloxane bridges were synthesized by Ni(0)-mediated copolymerization between 2,7-dibromo-9,9′-dihexylfluorene and a bridged fluorene monomer containing siloxane linkages. Two such bridged copolymers were prepared: PSiloBg1 (containing 1 mol % siloxane-bridged fluorene unit) and PSiloBg3 (containing 3 mol % siloxane-bridged fluorene unit). PSiloBg1 and PSiloBg3 exhibited good solubility in common organic solvents, thermal stability up to 420°C, and facile film formation. The glass transition temperatures of the bridged polymers (106 and 110°C , respectively) were higher than that of the homo poly(dihexylfluorene) (PDHF). In particular, PSiloBg3 exhibited a polymerization yield (96%) and a molecular weight (MW ) 185 000) higher than those of PDHF (polymerization yield ) 62%, MW ) 82 000). Interestingly, after the bridged polymers had been annealed at 150°C for 4 h in air, their PL spectra showed no significant increase in vibronic structures at 450 and 475 nm and no evidence of aggregation formation and excimers at wavelengths of >500 nm. In addition, the full width at half-maximum (fwhm) of the bridged polymers was very small (fwhm ) 51-52 nm) compared to that of PDHF (fwhm ) 85 nm). Collectively, the results show that the polyfluorenes with siloxane bridges exhibit thermally stable almost pure blue emission, making these polymers promising candidate materials for device applications.
“…Miller et al13a found that high-molecular weight fluorene copolymers may not exhibit any emission at longer wavelengths. The photoluminescent quantum yields of PSiloBg1 and PSiloBg3, which are listed in Table , are similar to those of PDHF . The PL quantum yields of PSiloBg1 and PSiloBg3 in solution were 0.83 and 0.86, respectively …”
Section: Resultsmentioning
confidence: 53%
“…The copolymers exhibited good thermal stability. As shown in Figure , the decomposition temperatures for 5% weight loss ( T d ) of the copolymers were above 420 °C, and the copolymers exhibited no significant weight loss upon being heated to ∼400 °C (see Table for T d values). 4 TGA traces and DSC thermograms of the polymers.…”
Section: Resultsmentioning
confidence: 98%
“…Subsequent work has established polyfluorenes as promising candidates for applications requiring blue light-emitting materials. Polyfluorenes have many properties that favor their use over other conjugated polymers in blue light-emitting applications. ,− They exhibit high photoluminescence (PL) and electroluminescence efficiencies, offer facile functionalization at the C-9 position of fluorene, and have good solubility in common organic solvents such as chloroform, toluene, and tetrahydrofuran (THF). − …”
The first novel polyfluorene copolymers containing siloxane bridges were synthesized by Ni(0)-mediated copolymerization between 2,7-dibromo-9,9′-dihexylfluorene and a bridged fluorene monomer containing siloxane linkages. Two such bridged copolymers were prepared: PSiloBg1 (containing 1 mol % siloxane-bridged fluorene unit) and PSiloBg3 (containing 3 mol % siloxane-bridged fluorene unit). PSiloBg1 and PSiloBg3 exhibited good solubility in common organic solvents, thermal stability up to 420°C, and facile film formation. The glass transition temperatures of the bridged polymers (106 and 110°C , respectively) were higher than that of the homo poly(dihexylfluorene) (PDHF). In particular, PSiloBg3 exhibited a polymerization yield (96%) and a molecular weight (MW ) 185 000) higher than those of PDHF (polymerization yield ) 62%, MW ) 82 000). Interestingly, after the bridged polymers had been annealed at 150°C for 4 h in air, their PL spectra showed no significant increase in vibronic structures at 450 and 475 nm and no evidence of aggregation formation and excimers at wavelengths of >500 nm. In addition, the full width at half-maximum (fwhm) of the bridged polymers was very small (fwhm ) 51-52 nm) compared to that of PDHF (fwhm ) 85 nm). Collectively, the results show that the polyfluorenes with siloxane bridges exhibit thermally stable almost pure blue emission, making these polymers promising candidate materials for device applications.
“…Essa classe de polímeros, alguns dos quais estão mostrados na Figura 2, tem despertado o interesse dos estudiosos por suas propriedades elétricas e ópticas com potencial aplicação para fabricação de dispositivos emissores de luz (LEDs) [22][23][24][25][26][27][28][29][30][31][32][33] . Estes polímeros apresentam algumas propriedades interessantes para essa finalidade destacando-se, entre elas, grande estabilidade química, térmica e oxidativa 18,[34][35][36][37][38] ; alto rendimento quântico de fluorescência tanto em solução quanto no estado sólido 37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] ; possibilidade de formarem materiais líquido-cristalinos 46,[58][59][60][61][62][63][64]…”
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...
“…7,10,42 The amount of anthracene moiety in copolymers was controlled by adjusting the ratio of feeding monomers (9,9-di(2'-ethylhexyl)-2,7-dibromofluorene and 9,10-dibromoanthracene). Details of the synthetic procedure were given in our previous report.…”
UV/vis absorption and photoluminescence (PL) spectroscopy were used to examine the photophysical properties of statistical copolymers, poly(9,9-di(2-ethylhexyl)fluorene-stat-anthracene), with the mole ratio of the anthracene group ranging from 0 to 20%. The incorporation of the anthracene group into the conjugated backbone of the polyfluorene affected the PL pattern and quantum yield of the isolated chain in a dilute solution. An investigation of the photophysical properties in solvent-nonsolvent system revealed the formation of low-energy non-emissive and emissive aggregates. The quantity of these aggregated species depends significantly on the mole ratio of anthracene group in the polymer backbone. The existence of only 5 mol% of anthracene in the copolymer causes significant suppression of the well-known green emission (λ~525 nm). However, a large quantity of non-emissive aggregates indicated by the red-shift peak at ~415 nm in absorption spectra still formed. Increasing the mole ratio of the anthracene group to 20% suppressed both types of aggregates. Measurements of the absorption and PL spectra in the thin films showed consistent results. Although annealing of the homopolymer polyfluorene films at 150 o C in a vacuum oven caused a drastic increase in green emission, only a slight change was detected in the PL spectra of the copolymers. The presence of oxygen during annealing promoted the green emission of the polymer films.
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