Preparation and Characterization of Polyion-Complexed Langmuir−Blodgett Films Containing an NLO Chromophore

Abstract

Polyion complexes formed by monolayers of quaternary ammonium amphiphiles containing the 4-nitro-4'-alkoxy azobenzene chromophore spread at the surface of aqueous solutions of a number of anionic polyelectrolytes were investigated. In general, pi-A isotherms were found to depend on the nature of the polyion present in the subphase, with monolayers of complexes involving polycarboxylates tending to exhibit larger limiting areas than those formed with polysulfonates or polysulfates. Monolayers of the polyion complexes can be transferred to hydrophilic solid substrates to yield Z-type LB films, although some peeling off for more than 10 layers is an impediment. X-ray reflectivity measurements indicate that relatively smooth and uniform films are obtained up to about 10 layers. Average layer thicknesses are, however, significantly smaller than extended molecular lengths, implying that the amphiphiles are strongly inclined from the surface normal. Polarized FT-IR measurements also indicate poor molecular orientation perpendicular to the surface. Preliminary SHG measurements for LB films of two systems, 12Q/CMC-Na and 12Q/PAA, confirm the presence of noncentrosymmetric out-of-plane chromophore ordering. Stable signals are observed for elevated temperatures up to 130 degrees C and for a period of 4 months at room temperature. To the best of our knowledge, this represents the first report of stable SHG in LB films of polyion complexes.

Structural characterization and properties of an azopolymer arranged in Langmuir and Langmuir–Blodgett films

“…Wegner [65] describes the induction of in-plane anisotropy during the deposition process, but in the examples shown in this paper the intensity of the bands increases in the parallel direction to the dipping process. Similar dichroic behavior has been observed previously by Panambur et al [66]. Although, they did not offered a specific mechanism to explain those observations, they proposed that the film anisotropy may be somehow related to the increased peeling off observed as the number of layers increased.…”

Spectroscopic properties of mixed Langmuir–Blodgett films of rhodamine dyes and poly(N,N-diallyl-N-octadecylamine-alt-maleic acid)

“…Since the chemical incorporation of dyes into amphiphilic polymers is painstaking and encounters various practical problems, two alternative strategies have been developed. Either the charged amphiphilic dyes are spread on sub-phases containing an oppositely charged polyelectrolyte, forming a polymer complex at the interface [15][16][17][18][19], or amphiphilic dyes are co-spread with polymeric amphiphiles [19,20] analogous to co-spreading with low-molecular-weight amphiphiles. Both strategies provide good results.…”

Ultrathin Luminescent Films of Rigid Dinuclear Ruthenium(II) Trisbipyridine Complexes

“…The research efforts devoted to the design and synthesis of suitable materials and the subsequent preparation of ordered LB films are mainly driven by the possible application of such films in, e.g., heterogeneous catalysis, [13,14] chemical [10,15] and biological sensors, [16] electrical and optical thin-film devices, [17,18] and (nonlinear) optics. [19][20][21] By virtue of the electronic and optical properties associated with the metal center, transition-metal complexes form another class of interesting compounds for thin-film applications and molecular materials, showing distinct advantages compared to organic molecules. Metal complexes offer the possibility for reversible redox chemistry and, owing to the ambipolar nature of their structure (e.g., oxidation on the metal and reduction on the ligands), the interesting feature of an excited state, created by a charge recombination reaction (electro(chemi)luminescence).…”