The preparation and characterization of a self-assembled material showing a high nonlinear response and good photostability to ultrashort laser pulses is presented. The material is built by alternate deposition of tetrakis(4-sulfonatophenyl) porphyrin diacid (H4TPPS2-) and poly(diallyldimethylammonium chloride) (PDDA) forming electrostatically self-assembled multilayers (ESAMs). UV-visible absorption and emission experiments show that in this matrix H4TPPS2- is present mainly in its J-aggregated form. Furthermore, linear dichroism experiments on a 3 bilayer film show a preferential alignment of the porphyrin aggregate with the J-band transition dipole moment parallel to the film surface. The two photon absorption (TPA) properties of these films are investigated with the Z-scan technique at 806 nm, employing 130 fs pulses. The samples exhibit strong nonlinearities with a very large two-photon absorption coefficient beta(TPA) of 50 cm GW(-1). The origin of this large response is investigated. It has been already demonstrated that aggregation enhances the molecular TPA cross section of H4TPPS2- from 30 to 1000 GM in water solution thanks to cooperative effects. In a 20 bilayer film a further increase by a factor of 1.7 is observed and explained in terms of preferential alignment of J-aggregates in the multilayer

The structure and composition of the mixed monolayer of hexadecyltrimethylammonium bromide and benzyl alcohol adsorbed at the air−water interface has been measured by using specular neutron reflection. The alkyl chain conformation of the hexadecyltrimethylammonium bromide at a surfactant concentration of 2 × 10-3M is not significantly altered by the addition of benzyl alcohol. However, the addition of benzyl alcohol draws the hexadecyltrimethylammonium bromide alkyl chain closer to the aqueous subphase:  a similar change is observed in the mixed monolayers of hexadecyltrimethylammonium bromide−hexaethylene glycol monododecyl ether and of sodium dodecyl sulfate−dodecanol. The distribution of the benzyl alcohol molecules in the interface is found to be centered on the third methylene group from the headgroup of the alkyl chain of the hexadecyltrimethylammonium bromide cationic surfactant.