The Langmuir-blodgett (lb), Two Amphiphilic Porphyrin Derivatives, The Nature Of The Film

Porphyrin derivatives have been extensively studied from the view point of modeling electron transfer processes in biological systems due to their special optical, electronic and magnetic properties and rigid macrocyclic structure. The Langmuir-Blodgett technique is a conventional and highly sophisticated method for fabricating organic ultra thin films in nanometer dimension, which are made by stepwise deposition of monolayer of amphiphilic from the air/water interface onto a solid substrate. Over the past decade, the Langmuir-Blodgett method has been widely used to construct ordered molecular assemblies of porphyrin. Porphyrin LB films show the properties of semiconductors, photoconductors, photovoltaic effects and nonlinear optical effects, and have potential applications as molecular devices and photoelectronic devices in the future. These properties are dependent on the electron interactions between porphyrin macrocycles in the films. The porphyrin macrocycle orientation and the intermolecular distances are important parameters for electron interactions. To realize molecular electronics or photoelectronics devices, it is necessary to handle the orientation of porphyrin macrocycles in LB films.It was reported that tetraphenylporphyrin (TPP) had a bad film-forming property on the air/water interface. In this thesis, three amphiphilic "tailed" porphyrin was designed and synthesized. Experiment results showed that stable monolayers could be formed.5, 10, 15-tri(p-chlorphenyl)-20-m-oxy(α-stearic acid)phenylporphyrin (TSPP) and 5, 10, 15-tri(p-chlorphenyl)-20-m-(6-chlortriethylene glycol)phenylporphyrin (TOPP) have been synthesized by reaction of 5, 10, 15-tri(p-chlorphenyl)-20-m-hydroxy phenylporphyrin with ethylα-bromostearate and dichloride of triethylene glycol. 5, 10, 15-tri(p-chlorphenyl)-20-m-(6-chlortriethylene glycol)phenylporphyrinCu (TOPPCu(II)) was obtained by the reaction of TOPP with Cu(OAc)2. These compounds were characterized by elemental analysis, IR, UV and ~1H NMR, respectively.The film-forming properties of three amphiphilic porphyrin on the air/water interface have been studied by surface pressure-area (π-A) isotherms. Effects of concentration and consumption of solution were also discussed. Theπ-A isotherms for these porphyrin derivatives showed that stable monolayers could be formed. Schematic models of amphiphilic porphyrin Langmuir monolayer formed at the air/water interface were suggested based on all considerations of surface pressure-area (π-A) isotherms, differential curves and static elasticity curves.The monolayers and multilayers of amphiphilic porphyrin were successfully deposited on the mica substrates by Langmuir-Blodgett method. The morphology of amphiphilic porphyrin LB films and spin-coating films were investigated by atomic force microscopy (AFM). The results showed that the optimal transfer surface pressure of TSPP, TOPP and TOPPCu(II) LB films were 35 mN/m, 27 mN/m and 30 mN/m, respectively. Compared with LB films of TSPP and TOPPCu(II) the TOPP LB films presented a relatively less flattened and condensed surface because of its weak adsorption to the substrate surface. However, the spin-coating films of TOPP were composed of a great number of identical shaped aggregations which were in a dot array arrangement. Further study is now in progress.The monolayers and multilayers of amphiphilic porphyrin LB films were deposited on hydrophilic quartz substrates by using the vertical dipping method at the optimal transfer surface pressure. Structures of LB films were investigated by UV-vis absorption spectrometry, small angle X-ray diffraction (SAXD) and nano-etching method. The UV-vis absorption peaks of LB films were red shifted compared with those in solution, indicating the existence of strong molecular interaction. The molecules of TSPP and TOPPCu(II) formed well-ordered stable monolayers with a face-to-face orientation and edge-on configuration on the air/water interface and solid substrates. Multilayers of TSPP and TOPPCu(II) LB films had good stability, homogeneity and periodicity. The orientation angles of the porphyrin macrocyclic of TOPPCu(II) and the alkyl chain of TSPP with respect to the substrate were calculated to be 59.6°and 52.3°, respectively.The electrochemical behaviors of TOPP and TOPPCu(II) LB films on glass carbon electrode and in DMF were investigated with cyclic voltammetry.