Investigation of the Aggregation Properties of a Chiral Porphyrin Bearing Citronellal Meso Substituent Groups

A new porphyrin bearing four R or S hydrogenated citronellal units directly bound to the meso positions of the porphyrin ring was synthesized and fully characterized through MALDI-TOF, NMR, UV/Vis absorption, and fluorescence emission spectroscopies. Both enantiomers exhibit a monomeric nature in a series of organic solvents. Acting on 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. Chirality 27:900-906, 2015.