fulltext42 - Ordered Self-assembly of Protonated Porphyrin...

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Ordered Self-assembly of Protonated Porphyrin Induced by the Aqueous Environment of Biomimetic Systems S UZANA M. A NDRADE AND ILVIA M. B. C OSTA Centro de Qu´ ımica Estrutural, Complexo 1, Instituto Superior T´ecnico, Lisbon, Portugal Water-soluble ionic porphyrins show an interesting self-association pattern in acidic conditions under which highly ordered aggregates are stabilized. Herein we give an overview of the tem- plate effect of biological interfaces in tetrakis(4-sulfonatophenyl)porphyrin TSPP self-aggregation, in which we point out the possibility of tuning this process by screening the charge repulsion through ionic strength and pH. We give special emphasis to the use of fluorescence lifetime imag- ing microscopy and of fluorescence correlation spectroscopy to visualize and characterize these molecular aggregates. Key words: self-assembly; light harvesting; porphyrin; proteins; reverse micelles; vesicles; carbon nanotubes; fluorescence lifetime imaging microscopy; fluorescence correlation spectroscopy Introduction In recent years, much attention has been focused on finding suitable conditions for the formation of nanostructured self-associated assemblies, which are expected to have important applications for the devel- opment of new technologies. Often these were inspired by attempts to mimic the highly efficient electron and energy transfer processes that take place in the light- harvesting complexes and reaction centers of photo- synthetic organisms. 1 Molecular dye aggregates also play an important role in many technological appli- cations and have been used as photoinduced molecu- lar switches, fluorescence sensors, photonic wires, and molecular elements for information storage. 2 The design of supramolecular assemblies based on porphyrinoids (e.g., porphyrins, phthalocyanines, chlo- rins, and porphyrazines) which display a rich variety of photonic properties has remained a challenge due on one hand to the difficulty of controlling the molecu- lar orientation in a desired fashion and on the other to overcome the lack of robustness that the relatively weak intermolecular forces involved confer to the material and prevent their incorporation into devices. 3 , 4 Thus, effective noncovalent synthesis requires an ensemble of Address for correspondence: Suzana M. Andrade, Centro de Qu´ ımica Estrutural, Complexo 1, Instituto Superior T´ecnico, 1049-001 Lisbon, Portugal. Voice: + 351-21-8419389; fax: + 351-21-8464455/7. suzana.andrade@ist.utl.pt interactions, such as hydrogen bonding, electrostatic, van der Waals, and hydrophobic, to build well-defined supramolecular structures. Molecular Aggregates Electronic excitation of molecular aggregates often results in emission dynamics that differ from that of isolated molecules due to the formation of Frenkel ex- citons. These excitons are delocalized as a result of in- termolecular coupling between molecules. Sharing of excitation, leads to aggregates with unique electronic and spectroscopic properties. J- or H-aggregates are
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This note was uploaded on 07/11/2010 for the course SPECTOGRAP 545 taught by Professor Gdf during the Spring '10 term at AIB College of Business.

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fulltext42 - Ordered Self-assembly of Protonated Porphyrin...

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