Influence of magnetic micelles on assembly and deposition of porphyrin J‐aggregates

Clusters of superparamagnetic iron oxide nanoparticles (SPIONs) have been incorporated into the hydrophobic core of polyethylene glycol (PEG)‐modified phospholipid micelles. Two different PEG‐phospholipids have been selected to guarantee water solubility and provide an external corona, bearing neutral (SPIONs@PEG‐micelles) or positively charged amino groups (SPIONs@NH2‐PEG‐micelles). Under acidic conditions and with specific mixing protocols (porphyrin first, PF, or porphyrin last, PL), the water‐soluble 5,10,15,20‐tetrakis‐(4‐ sulfonatophenyl)‐porphyrin (TPPS) forms chiral J‐aggregates, and in the presence of the two different types of magnetic micelles, an increase of the aggregation rates has been generally observed. In the case of the neutral SPIONs@PEG‐micelles, PL protocol affords a stable nanosystem, whereas PF protocol is effective with the charged SPIONs@NH2‐PEG‐micelles. In both cases, chiral J‐aggregates embedded into the magnetic micelles (TPPS@SPIONs@micelles) have been characterized in solution through UV/vis absorption and circular/linear dichroism. An external magnetic field allows depositing films of the TPPS@SPIONs@micelles that retain their chiroptical properties and exhibit a high degree of alignment, which is also confirmed by atomic force microscopy.