Abstract
The hierarchical self-assembling kinetics of the porphyrin 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2TPPS44−) into J-aggregates at high ionic strength under acidic conditions and eventually in the presence of an added chiral templating agent (tartrate) were investigated through UV/Vis spectroscopy, resonance light scattering, and circular dichroism (CD). The effect of changing the mixing order of the various components in the solution on the kinetic parameters and the expression of chirality on the final J-aggregates was evaluated. In this latter case, only when the chiral tartrate anion is premixed with the porphyrin, the resulting nano-architectures exhibit CD spectra that reflect the handedness of the chiral inducer. We discuss a general mechanistic scheme, with the involvement of ion pairs or dimers that offer an alternative pathway to the aggregation process.
Highlights
Aggregation of porphyrins is a general phenomenon occurring in this class of compounds and is mainly ascribable to different intermolecular forces acting among the basic monomeric units [1]
5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (H2 TPPS4 4− ) have received a lot of attention since they are soluble in water, and aggregation can be triggered by a proper choice of experimental conditions [5,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31]
In previous studies we demonstrated that in a simple acid triggered aggregation, if the acid is added to a pre-diluted porphyrin solution (referred as porphyrin first (PF) protocol), the kinetics evolve through a slow nucleation phase or lag-time, followed by a quite fast autocatalytic growth [27]
Summary
Aggregation of porphyrins is a general phenomenon occurring in this class of compounds and is mainly ascribable to different intermolecular forces acting among the basic monomeric units [1]. On changing the mixing order, the difference in kinetic behavior is so striking that a sort of “YES/NO” effect has been pointed out in literature This occurs especially at low porphyrin concentration, where the concentration effect impacts the rates, slowing down dramatically the aggregation process [23,56]. We showed that using a PL protocol and changing the concentration of porphyrin and the overall ionic strength, different mesoscopic structures were obtained, i.e., fractal clusters at low porphyrin concentration and high ionic strength, and rod-like aggregates at higher porphyrin concentration and lower ionic strength In both regimes, chiral selection has been detected as consequence of the handedness of the inducer (tartrate), even if the sign of the observed CD spectra for the same enantiomeric form of the chiral anion was reversed by changing the overall structural arrangement [24].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
