Synthesis and photophysical properties of a poly(methyl methacrylate) polymer with carbazolyl side groups

Abstract

As propriedades fotofísicas de um poli(metacrilato de metila) (PMMA) contendo 1,6 mol % de grupos etil-carbazolila aleatoriamente distribuídos pela cadeia, foram estudadas pelas técnicas de espectroscopia de fluorescência em condições fotoestacionárias e com resolução temporal. O material foi preparado a partir da esterificação do poli(metacrilato de metila-co-ácido metacrílico) com 9H-carbazolila-9-etanol. A temperatura ambiente, o espectro de fluorescência que se obtém para a amostra em solução é devido ao lumóforo isolado. Em filme, suas características espectroscópicas se tornam mais complexas, com contribuições do lumóforo isolado, dímeros formados no estado eletrônico fundamental e excímeros. A 77 K, a emissão obtida das amostras, tanto em filme quanto em solução, apresenta também a contribuição da fosforescência, que ocorre na mesma região espectral que a emissão de fluorescência dos agregados emissores. Os diversos tipos de relaxações mecânicas do polímero puderam ser observados através dos espectros de fluorescência do filme, obtidos na faixa de temperatura de 30 a 410 K e são similares àqueles relativos ao PMMA. Os dados obtidos por calorimetria diferencial de varredura (DSC) e análise térmica dinâmico-mecânica (DMTA) são comparados aos dados fornecidos pela espectroscopia de fluorescência e as temperaturas onde ocorrem estas relaxações puderam ser determinadas. Assim os processos da γ-relaxação, que é resultante de movimentos de pequenos segmentos de cadeia, ocorrem a 120-130 K (observados por espectroscopia de fluorescência), a β-relaxação, resultante dos movimentos de grupos éster laterais (observada por DMTA e espectroscopia de fluorescência), a 310 K e α-relaxação (temperatura de transição vítrea) ocorre a 380 K (observada por DSC e DMTA).The photophysical properties of solutions and films of poly(methyl methacrylate) (PMMA) containing 1.6 mol % of randomly distributed pendant ethyl carbazolyl groups have been studied under steady-state and time-resolved conditions. The polymer was prepared by esterification of poly(methyl methacrylate-co-methacrylic acid) by 9H-carbazole-9-ethanol. At room temperature, the steady-state fluorescence spectrum is attributed to isolated lumophores in solution, but is much more complex in films where emission is detected from isolated groups, ground-state dimers and excimers. At 77 K, emission from both solutions and films contains a component of phosphorescence whose wavelengths overlap fluorescence from excited ground-state dimers and excimers. From the temperature dependence of the steady-state emission spectra of the films, recorded from 30 to 410 K, several types of relaxation processes are identified at temperatures similar to those of unmodified PMMA. Data by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and fluorescence spectroscopy are compared. They include the γ-relaxations from motions of small segments of the chains at 120-130 K (by fluorescence spectroscopy), the β-relaxation from motions of lateral ester groups (by ...

Energy Transfer from Poly(Vinyl Carbazole) to a Fluorene‐Vinylene Copolymer in Solution and in the Solid State†

“…The excitation and PL spectra appear to be mirror images, but the Stokes shift is greater (2237 cm −1 , considering the band peak) than that observed in solution, suggesting that this polymer undergoes aggregation in the solid state. The Stokes shift also indicates that several types of relaxation processes become possible after excitation (including energy migration), as has been observed for other conjugated polymers (31).…”

“…This blue‐edge component may be attributed to the excitonic splitting of the π‐π stacking aggregates (15,51). Aggregation by π‐π stacking is very common in conjugated polymers with planar conformations (14,15,31,44–47). The PL spectrum (λ exc = 450 nm) is also broader and redshifted with the zero‐phonon band at 514 nm and the 0–1 transition at 541 nm.…”

“…The steady-state emission of the isolated carbazolyl groups is observed as a shoulder in the blue-edge of the emission band centered at k em = 400 nm; thus, the component with s F1 = 1.83 ns may be attributed to the carbazolyl groups undergoing quenching due to their proximity to longer sequences of carbazolyl moieties. The slower component may be attributed to excimer emission (28)(29)(30)(31)(32)(33)(34)(35). Figure 2 also shows a strong overlap between the PL spectrum of the PVK and PFO-MEHPV electronic absorption spectra, suggesting that mixtures of these two materials may undergo either FRET or trivial energy transfer from PVK to the polyfluorene.…”

“…Poly(vinyl carbazole) has very complex intrinsic photophysical pathways after electronic photoexcitation that competes with the energy transfer process to an extrinsic acceptor (28)(29)(30)(31)(32)(33)(34)(35)(36). Some of these pathways are related to the presence of intrachain trapping centers, such as the excimer-forming traps (27)(28)(29)(30)(31)(32)(33)(34)(35). When the monomer-like emission (singlet excitons) is absent, as observed in the present system, the energy migration from the excited state monomer units toward the excimer-like trap is very efficient.…”

Relaxation Processes and Polymeric Chain Interpenetration in a PMMA-Cz/ MEH-PPV Blend Studied by Fluorescence Spectroscopy

“…Blends were prepared from Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]-MEH-PPV (Sigma-Aldrich, Mn=84,000 g/mol) and a pre-obtained poly(methyl methacrylate -co-methacrylic acid) 1.0:0.016 (Mn ~ 15 kg mol-1 e Mw ~ 34 kg mol-1) modified with 9-vinyl-carbazolyl fluorescent pendant groups-PMMA-Cz [9], was characterized by FT-IR spectroscopy, as showed elsewhere [9] and had its molar contents of the carbazolyl moieties determined spectroscopically. UV/Vis absorption spectra were recorded using a dual-beam Perkin-Elmer Lambda-6 spectrophotometer and a calibration curve from standard solutions of 9HCz in chloroform (with molar concentrations ranging from 5 10 -7 to 1 10 -4 mol L -1 ) was plotted.…”