Self-assembly of aromatic-derivatized amphiphiles: Phenyl, biphenyl, and terphenyl fatty acids and phospholipids

This paper reports the synthesis of a series of amphiphiles (fatty acids and phosphatidylcholine derivatives) containing phenyl, biphenyl, and terphenyl chromophores inserted in the hydrocarbon chain and a study of their self-assembly in Langmuir-Blodgett films and aqueous dispersions. As observed and reported earlier for amphiphiles containing trans-stilbene, styrylthiophene, or azobenzene chromophores, several of the biphenyl and terphenyl derivatives show strong evidence of ground state association to form "H" aggregates characterized by a blue shift in absorption and a structured red-shifted fluorescence. The phenyl amphiphiles show different behavior, suggesting that, even for pure films or bilayers, there is very little or no ground state association. For the biphenyl and terphenyl phospholipids, aqueous suspensions obtained by sonication are closed bilayer vesicles similar in size to those formed from the corresponding saturated phospholipids. The overall results of the present study indicate that biphenyl and terphenyl amphiphiles undergo aggregation processes to form compact arrays formally similar to those observed with stilbene, tolan, azobenzene, and squaraine derivatives but that the aromatic-aromatic interactions are considerably weaker than those for the more extended aromatics and lead to less distortion of the assembly structure.