In this work, supramolecular l - l -diphenylalanine (Phe–Phe) nanostructures were self-assembled in solvents of distinct polarity and in the presence of luminescent additives of distinct conjugation length that physically adhere to the nanostructures to provide growth environments of distinct properties. When the additive is poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], an electron donor polymer, and solvent is tetrahydrofuran (THF), Phe–Phe vesicle-like structures are obtained, whereas in water and in the presence of a similar additive in structure, poly[5-methoxy-2-(3-sulfopropoxy)-1,4-phenylenevinylene], nanotubes are formed. In contrast, when 9-vinyl-carbazole, an electron acceptor additive is used, nanotubes are formed even when THF is the solvent. The same structures are obtained when the additive is the macromolecule poly(vinyl carbazole). The morphologies of these self-assembled structures were observed by scanning electron microscopy, and their photophysical behavior was determined by steady-state fluorescence spectroscopy and time-resolved fluorescence spectroscopy. These data analyzed altogether inform about the formation mechanisms of such structures and about the influence that distinct interactions exert on self-assembling and charge-transfer processes through formation of complexes between the luminescent additives and the Phe–Phe nano- and microstructures.
It is incontestable that the interactions and bonds that keep molecules united to generate unique supramolecular compounds, with individual properties, morphologies and behaviour, are of special dynamics and singular forces. Therefore, it is necessary to discuss and consider the types of interactions that may occur in a determined system, their dynamics and number, which directly act on the energetic balance that strengthen the union between participants and give rise to a supramolecule.In this chapter, a number of such supramolecular systems that find application as any component of a biosensor are presented and discussed, considering intermolecular interaction forces that confer them shape, function and unique properties. To better understand their structural dynamics and the mechanisms through which they can be used in biosensing, a brief explanation on the interaction thermodynamics, types of intermolecular interactions that compete against each other and the energetic equilibrium that originate and stabilize supramolecular systems is given. To explain how this balance of forces can be extensively exploited to develop methods to produce supramolecular compounds, an overview on supramolecular strategies is presented and their contribution is explored in each example presented in this text, to evidence the importance of planning and developing methodologies of preparation, based on
This work will show an overview of the hydrogen production from ethanol by steam reforming method, using distinct catalysts, resulting in low carbon monoxide content in H2 produced; a thermodynamic analysis of reforming employing entropy maximization, the ideal condition for ethanol, and other steam reforming reactions, the state of the art of steam reforming catalysts for H2 production with low CO content. Moreover, in the second part, there will be an overview of the use of hydrogen in a proton exchange membrane fuel cell (PEMFC), the fuel cell operational conditions, a thermodynamic analysis of PEMFC, the catalysts used in the electrodes of the fuel cell, consequences of the CO presence in the hydrogen fuel feed in PEMFC, and the operation conditions for maximum output power density.
In this work, single-layered, bi-layered and tri-layered poly(vinyl-carbazole) (PVK) thin films were produced by spin-coating and self-assembling techniques and their morphological and photophysical properties were determined by time-resolved fluorescence spectroscopy, atomic force microscopy (AFM) and fluorescence microscopy. The effect of distinct aggregates formed in thin films on their photophysical and morphological properties was determined, evidencing that procedure control is essential to determine PVK thin film application. It was found that sandwich excimers are dominant in self-assembled films, evidenced by longer fluorescence lifetimes and red-shifted emissions, while in spin-coated films, shorter fluorescence lifetimes evidenced more efficient non-radiative energy transfer. AFM showed that consecutive deposited layers result in more uniform, thinner films when produced by spin-coating, but showing aggregation heterogeneity as evidenced by fluorescence spectroscopy. Yet, self-assembled films are rough, heterogeneous and thicker, showing prevalence of less variety of aggregates. These are crucial findings to address PVK application.
Kinetic rates of energy production are extremely controlled by the competing processes that occur in systems capable of energy transfer. Besides organic and inorganic compounds already known as electronically actives, supramolecular systems can be thought to form energy transfer complexes to efficiently convert, for instance, light into electricity and the mechanisms for that can be of any kind. Photophysical and photochemical processes can simultaneously occur in such systems to provide energy conversion, by competing mechanisms or collaborative ones. Thus, to investigate the kinetic rates of each process and to understand the dynamics of the electronic excited states population and depopulation in strategically structured materials, can offer important tools to efficiently make use of this not always so evident power of supramolecular materials. In this chapter, we present the state-of-the-art of the use of photophysical processes and photochemical changes, presented by new materials and devices to provide a control of energy transfer processes and enable distinct applications, since energy conversion to sensing and imaging techniques to material characterization.
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