Stirring Effects on the Spontaneous Formation of Chirality in the Homoassociation of Diprotonatedmeso-Tetraphenylsulfonato Porphyrins

Abstract

Homoassociates of the achiral title porphyrins in acid solutions show spontaneous symmetry breaking, which can be detected by circular dichroism (CD). The CD spectra are due to differential scattering and differential absorption contributions, the relative significance of which is related to the shape and size of the homoassociate. When an earlier model, designed for the association of these diprotonated porphyrins (J aggregates with the geometry of stepped sheets of intramolecularstabilised zwitterions), was applied to an exciton-coupling point-dipole approximation, the folding of the onedimensional homoassociates explained the CD signals detected. An effect of the vortex direction, caused by stirring or rotary evaporation, upon the exciton chirality sign was detected. In the case of H 2 TPPS 3 , the number of experiments performed gave a statistical significance to this effect. This vortex effect can be attributed to enhancement of the chirality fluctuations that originate in the diffusion-limited aggregation to highmolecular-weight homoassociates. In this sense, the phenomenon could be general for supramolecular systems that are obtained under kinetic control, and its detection would be possible when inherent chiral chromophores were being generated in the association process. H , B J and Q bands of all compounds and experiments. Example of the evolution of a metastable solution.

Exciton relaxation in nanotubular TPPS4 aggregates in water solution and in polymeric matrix

“…Various spectroscopic methods have been applied to define electronic structure [14][15][16][17][18] and exciton dynamics [19][20][21][22] in TPPS 4 aggregates. Recent investigation of TPPS 4 J-aggregates in polyvinyl-alcohol by means of electroabsorption spectroscopy suggested that excitons in these structures are coherently delocalised over 60-80 monomer molecules [23].…”

A Supramolecular Chiroptical Switch Based on Chitosan and Anionic Porphyrin Complex Film

“…It is well known that TPPS aggregates are easily induced to show CD activity by achiral molecules or even by mechanical stirring. 31 The chirality of TPPS aggregates is normally attributed to the helical formation of the TPPS aggregates due to the broken of the mirror-symmetry of the diprotonated porphyrins in the TPPS aggregates or the formation of a 90 fold of the TPPS aggregates. 31 It has been reported that in tryptophan chiral L-or D-isomers solutions, the chirality of the TPPS aggregates always follows the chiral molecules and the TPPS aggregates form Lor D-helix respectively.…”

“…31 The chirality of TPPS aggregates is normally attributed to the helical formation of the TPPS aggregates due to the broken of the mirror-symmetry of the diprotonated porphyrins in the TPPS aggregates or the formation of a 90 fold of the TPPS aggregates. 31 It has been reported that in tryptophan chiral L-or D-isomers solutions, the chirality of the TPPS aggregates always follows the chiral molecules and the TPPS aggregates form Lor D-helix respectively. 45 Moreover, the chirality of the TPPS J-aggregates in the complex L-or D-Trp multiplayer films formed via ex situ also follows the chirality of films.…”

An Introduction to Chirality at the Nanoscale

“…There has been considerable interest in the possibility that vortex motion in a conical swirl might be exploited to induce absolute enantioselection, but until recently no convincing example has been demonstrated experimentally [67]. Then -several years ago reports appeared of mirror-symmetry breaking in homoassociation of achiral diprotonated porphyrins where helical conformations were generated by stirring in a rotary evaporator with the sense of chirality, detected by circular dichroism, being selected by the sense of stirring [70,71]. In a later report, the same group claimed to have achieved similar results through magnetic stirring in a small tube, and went on to provide an explanation in terms of hydrodynamic effects of the vortex at the walls of the container [72].…”