Organization at higher levels is extremely intriguing in the case of achiral molecules that self-assemble in the presence of a chiral bias to afford chiral supramolecular complex structures. J-aggregates of the achiral TPPS4 porphyrin represent a nice example that recently is gaining attention for their peculiar optical and structural features. The use of optically active tartaric acid as chiral inducer has been reported as the first example of organic aggregates showing magneto-chiral dichroism. As part of our interest, we have also shown an interesting structural transition from fractal to rod-like aggregates, that depends on the porphyrin concentration and the ionic strength and that is responsible for a peculiar inversion of the circular dichroism spectra with the same templating enantiomer. Chiral porphyrin nanoaggregates have been confined into microemulsions water pools achieving a remarkable scaling of the quality of the circular dichroism signal on the dimension from the nano- up to mesoscopic regime. Here we report on the chiral induction mediated by the two different isomers of the i) tartaric acid, ii) mandelic acid and iii) camphorsulfonic acid. The acids have been selected to have variability in terms of structure and strength. The results obtained have allowed to gain important information in the field of supramolecular architectures, highlighting the importance of the role of experimental parameters such as concentration and/or mixing order of the reagents. The systems have been investigated through a combination of UV/Vis absorption, circular dichroism and resonance light scattering. In the case of tartaric acid, the kinetics of growth for chiral TPPS4 J-aggregates have been fully investigated under different experimental conditions. We anticipate that, depending on the overall rate of the process, a distinctive kinetic difference, together with a variance in the extent of the chiral transfer, is clearly evident for the two enantiomers of the tartaric acid
Optically active TPPS J-Aggregates induced by chiral acids
R Zagami;A Romeo;
2013
Abstract
Organization at higher levels is extremely intriguing in the case of achiral molecules that self-assemble in the presence of a chiral bias to afford chiral supramolecular complex structures. J-aggregates of the achiral TPPS4 porphyrin represent a nice example that recently is gaining attention for their peculiar optical and structural features. The use of optically active tartaric acid as chiral inducer has been reported as the first example of organic aggregates showing magneto-chiral dichroism. As part of our interest, we have also shown an interesting structural transition from fractal to rod-like aggregates, that depends on the porphyrin concentration and the ionic strength and that is responsible for a peculiar inversion of the circular dichroism spectra with the same templating enantiomer. Chiral porphyrin nanoaggregates have been confined into microemulsions water pools achieving a remarkable scaling of the quality of the circular dichroism signal on the dimension from the nano- up to mesoscopic regime. Here we report on the chiral induction mediated by the two different isomers of the i) tartaric acid, ii) mandelic acid and iii) camphorsulfonic acid. The acids have been selected to have variability in terms of structure and strength. The results obtained have allowed to gain important information in the field of supramolecular architectures, highlighting the importance of the role of experimental parameters such as concentration and/or mixing order of the reagents. The systems have been investigated through a combination of UV/Vis absorption, circular dichroism and resonance light scattering. In the case of tartaric acid, the kinetics of growth for chiral TPPS4 J-aggregates have been fully investigated under different experimental conditions. We anticipate that, depending on the overall rate of the process, a distinctive kinetic difference, together with a variance in the extent of the chiral transfer, is clearly evident for the two enantiomers of the tartaric acidI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
