INVERSE KINETIC AND EQUILIBRIUM ISOTOPE EFFECTS ON SELF-ASSEMBLY AND SUPRAMOLECULAR CHIRALITY OF PORPHYRIN J-AGGREGATES

Symmetry breaking in non-covalent supramolecular assemblies of achiral building blocks in the absence of chiral perturbations were greeted, at first, with skepticism. However, now that these findings have been confirmed, considerable attention has been focused on this phenomenon. Achiral chromophores, especially porphyrins, have been of some considerable importance for such symmetry-breaking studies due to their rich spectral properties and their ability (under appropriate conditions) to self-assemble into chiral supramolecular structures. In particular, J-aggregates of the water soluble mesotetrakis( 4-sulfonatophenyl)porphyrin (TPPS4) provide an iconic example of such behaviour.2 Many studies carried out on this system have allowed to gain important information in the field of supramolecular architectures, highlighting the importance of the role of experimental parameters such as kinetic rates, concentration and/or mixing order of the reagents.3,4 Here, we report a kinetic and spectroscopic study on the formation of J-aggregates of TPPS4, using solvent mixtures containing increasing amounts of deuterium. We found that the system exhibits inverse kinetic and equilibrium isotope effects and that the chirality of the nanoaggregates is inverted in the presence of a small amount of deuterium, with respect to the normal protiated solvent.