Host−Guest Chemistry Using an Oriented Mesoporous Host:  Alignment and Isolation of a Semiconducting Polymer in the Nanopores of an Ordered Silica Matrix

Abstract

Oriented polymer/silica composites have been synthesized by incorporating the conjugated semiconducting polymer MEH-PPV into the pores of an aligned, hexagonally ordered mesoporous silica. The ordered silica framework is synthesized by a silica/surfactant coorganization process that proceeds via a silicate/surfactant liquid crystalline intermediate. Magnetic fields are used to orient this liquid crystalline intermediate, followed by chemical cross-linking of the silica framework and removal of the surfactant. Hexagonally ordered (p6mm) aligned silica samples are treated with organic chlorosilanes to optimize interactions between the polymer and the silica surface. Polymers are incorporated from solution; thermal cycling is used to drive the polymers into the pores. The resultant polymer incorporation is monitored by polarized photoluminescence spectroscopy. Polymer chains which are oriented in the aligned nanoporous silica show strong polarization anisotropy in their photoluminescence (I VV/I VH = 4.4, I HH/I HV = 0.68 for vertically oriented pores). Spectroscopic results are compared to the results of a geometric model for transition dipole orientations and used to conclude that as much as 0.8 of the incorporated polymer is isolated within the nanopores of the silica matrix, while as little as 0.2 is located in the macroporous regions formed between grains of the silica host. Intentional oxidation can be used to degrade the polymer not isolated within the porous silica. After oxidation, essentially all of the photoactive polymer appears to be contained within the oriented silica matrix (I VV/I VH = 5.7, I HH/I HV = 0.71). The results prove that a semiconducting polymer can be isolated within the pores of an ordered silica host and that this isolation can be used to control the optical properties of the guest molecules (in this case the polarization). Further, the ability to simply characterize the degree of polymer incorporation using optical techniques allows us to learn about the effects of processing variables such as the role of surface chemistry, pore size, and thermal cycling on the final degree of polymer incorporation.

Determination of the Hyperpolarizability Components of Hemicyanine Dyes by Measuring the Anisotropic Fluorescence and Second Harmonic of the Dyes Uniformly Aligned within Zeolite Channels

“…Previous SHG experiment found the alignment of the dyes is not only uniform, but also quite unidirectional when the alkyl chain at one end of the molecule becomes long enough. 28 With the very unidirectional angular distribution as well as the molecules in isolation with minimal interaction with the host matrix, 26,27 our sample is a very good system for studying various optical properties. We utilized it to determine the hyperpolarizability components of the embedded hemicyanine molecules.…”

“…Light-emitting polymer molecules were incorporated into uniformly aligned channels of mesoporous silica to realize an artificial light-harvesting unit. 26,27 In that work with a rather large-sized pore (22 Å), the alignment of the polymer chains as inferred from polarization dependence of fluorescence was less than ideal as the main focus of the work was not the alignment of chromophores, but controlled energy migration. To characterize various optical properties as well as for practical applications such as lasers and nonlinear optical media, it would be highly desirable to have a matrix of macroscopic size where molecules can be embedded in a uniformly aligned way.…”

Películas fluorescentes azules basadas en derivados de poli-2,7-fluorenofenilideno

“…Sin embargo, hay que tener presente que se modifican o cambian las propiedades de los polímeros conjugados dependiendo de la capacidad de dispersión de cada lote de fabricación (7). La obtención de polímeros conjugados cargados mejoraría la aplicabilidad de las sondas fluorescentes en análisis directos de moléculas biológicas (7,8) o en la incorporación de composiciones iniciales de matrices inorgánicas (9,10).…”

“…Esta metodología de trabajo permite controlar las propiedades macroscópicas del composite y se convierte en una sugerente propuesta para la búsqueda de nuevos materiales (10). Algunas de las sugerencias más interesantes que aporte mejoras en sus propiedades ópticas se están desarrollando mediante sistemas hidrofílicos-hidrofó-bicos en la preparación de estructuras hexagonales altamente ordenadas y con un preciso control en el tamaño del poro obtenido (12).…”

Study of Anisotropic Photoluminescence and Energy Transfer in Oriented Dye-incorporating Zeolite-L Monolayer

“…Interestingly, the direction of energy transfer is the opposite to the case of polymer-containing mesoporous silica. [19][20][21] For more quantitative interpretation of energy transfer among the intrachannel and external PyB + ions, we investigate the angle-dependent changes of IVθ/IVH and IHθ/IHV ratios, where IVθ and IHθ represent the intensity of the spectrum of 'PyB Compared with polymeric fluorescent, it is expected that PyB + ions relatively easy to intercalate and be aligned within porous materials due to small size and light weight. And, based on the fact that our surface treatment of 'v-(PyB + )L-g' is crucial for preventing the egress of the incorporated PyB + ions from the channels to the solution, we believe that it plays an important role to enhance the anisotropic luminescence.…”