Novel amphiphilic phthalocyanines: Formation of Langmuir-Blodgett and cast thin films

The synthesis and solution and thin film characterization of four octasubstituted phthalocyanines (Pcs) are reported. [2,3,9,10,16,17,23,24-octakis(dodecylcarboxylato)phthalocyaninato]copper, [2,3,9,10,16,17,-23,24-octakis(N-dodecylamide)phthalocyaninato]copper, and [2,3,9,10,16,17,23,24-octakis(2-(benzyloxy)-ethoxy)phthalocyaninato]copper, and the corresponding zinc phthalocyanine analog, were prepared and their aggregation properties characterized in chloroform solutions. The octa-ester-modified Pes showed the greatest tendency toward solution aggregation (K_agg ≥ 4.8 × 10⁶), and the octakis((benzyloxy)ethoxy)-modified Pcs showed the least tendency toward aggregation (290 ≤ K_agg ≤ 1300). Both cast and Langmuir-Blodgett (LB) thin films of these compounds showed the tendency toward formation of columnar aggregates, as evidenced by their blue-shifted Q-band absorbance spectra. Fully compressed thin films of these Pcs show the rings tilted by ca. 50-60° with respect to the surface normal, with essentially cylindrical symmetry of the side chains about each aggregate. The octaester Pcs, which showed the strongest solution aggregation tendencies, proved to form the most highly ordered LB thin films, as evidenced by the dichroism in several key vibrational bands. Molecular dynamics simulations are presented which show hypothetical structures for single molecules of each of the above compounds, as well as pentamer linear cofacial aggregates which demonstrated stability in these calculations and which are structures consistent with the spectroscopic characterizations of these materials.