Expression of chirality at the supramolecular level is a complex phenomenon that is strictly dependent on the intermolecular interactions, the intrinsic chiral behavior of the molecular building blocks, and/or any external chiral field able to influence the resulting assemblies.1-2 Organization at higher levels of chiral components could lead to rather peculiar constructions for the development of chiroptical devices, catalysts, or chiral sensors.3 Among various systems, self-assembled porphyrin aggregates are fascinating materials in which the control over the spatial arrangement of the individual components at the nanometer scale can be achieved acting on the substituent groups present on the periphery of the aromatic rings.4-5 In this context, optically active porphyrins bearing a chiral center opportunely located in the periphery of the macrocycle have been synthesized for realizing chiral building blocks able to assemble into supramolecular helical structures.6 Here we report a new optically active porphyrin derivatives functionalized with four R or S citronellal units directly bound to the meso positions of the porphyrin ring. These latter were fully characterized through MALDI-TOF, NMR, UV/Vis absorption and fluorescence emission spectroscopies. These molecules exhibit a monomeric nature in a series of organic solvents. By changing the polarity of the solvent, i.e., increasing the amount of water in mixture with acetone, aggregation occurs as revealed by UV/Vis absorption, fluorescence emission and resonance light scattering. The occurrence of both H- and J-type aggregates was suggested by fluorescence lifetime measurements. In contrast to the monomeric species, these aggregates exhibit CD spectra reflecting the chirality of the building blocks. AFM microscopy shows that micrometer ribbon-like structures form by the casting solution of these porphyrins in acetone/water onto a glass surface. The design of such self-assembled systems allows to demonstrate the role of weak chiral perturbation on the expression and transmission of chirality from the molecular to supramolecular level.
Investigation on the aggregation properties of a chyral porphyrin bearing citronellal meso substituent groups
Roberto Zagami;Mariachiara Trapani;
2015
Abstract
Expression of chirality at the supramolecular level is a complex phenomenon that is strictly dependent on the intermolecular interactions, the intrinsic chiral behavior of the molecular building blocks, and/or any external chiral field able to influence the resulting assemblies.1-2 Organization at higher levels of chiral components could lead to rather peculiar constructions for the development of chiroptical devices, catalysts, or chiral sensors.3 Among various systems, self-assembled porphyrin aggregates are fascinating materials in which the control over the spatial arrangement of the individual components at the nanometer scale can be achieved acting on the substituent groups present on the periphery of the aromatic rings.4-5 In this context, optically active porphyrins bearing a chiral center opportunely located in the periphery of the macrocycle have been synthesized for realizing chiral building blocks able to assemble into supramolecular helical structures.6 Here we report a new optically active porphyrin derivatives functionalized with four R or S citronellal units directly bound to the meso positions of the porphyrin ring. These latter were fully characterized through MALDI-TOF, NMR, UV/Vis absorption and fluorescence emission spectroscopies. These molecules exhibit a monomeric nature in a series of organic solvents. By changing the polarity of the solvent, i.e., increasing the amount of water in mixture with acetone, aggregation occurs as revealed by UV/Vis absorption, fluorescence emission and resonance light scattering. The occurrence of both H- and J-type aggregates was suggested by fluorescence lifetime measurements. In contrast to the monomeric species, these aggregates exhibit CD spectra reflecting the chirality of the building blocks. AFM microscopy shows that micrometer ribbon-like structures form by the casting solution of these porphyrins in acetone/water onto a glass surface. The design of such self-assembled systems allows to demonstrate the role of weak chiral perturbation on the expression and transmission of chirality from the molecular to supramolecular level.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
