Study On Preparation And Properties Of Porphyrin LB Films

Porphyrin is a kind of material for maintaining plant and animal life. It can bewidely used in a variety of biological activities. Because of its large conjugatedporphyrin ring structure and pi-conjugated, people also pay large attention to itsspectral properties. LB（Langmuir-Blodgett）technology has a lot of advantages, suchas the molecular order, controllable thickness and so on. So it can be used inbiological membrane and chemically modified aspects. Combining the photoelectricproperties of good prophyrin itself with LB technology, we prepared the porphyrin LBfilms to study the electrochemical and spectral properties. We hope to discuss theporphyrin molecules order and charge transfer on the ITO electrode. Moreover, wereveals the relationship between its structure and function. It has importantsignificance for the charge transfer mechanism on chemically modified electrode fromthe molecular level.In this paper we fistly introduces the method of preparing LB film, porphyrins andfour level energy model theory. Then the porphyrin UV-visible absorption spectra andmainly infrared absorption peaks were identified. We also tested the fluorescencespectra and expounds the fluorescence mechanism. In the fourth chapter the porphyrinLB films prepared on the ITO substrate were assembled by the spectra method(UV-Vis absorption spectroscopy, infrared spectroscopy) and electrochemical(including cyclic voltammetry and constant potential jump method) to study thecharge transfer and storage properties characteristics of porphyrin LB films. Theresults show that the ordering and the layer-number of LB films all affect chargetransfer: As the ordering increases, the conductivity increases; electrical conductivitydecreases with the increase of layer number. UV-Vis spectrum show that orderedfilms form with the surface pressure of about10mN/m and disordered membranesform without surface pressure. The ordered and disordered mix when the surfacepressure is about5mN/m. The formation of ordered membrane has been furtherconfirmed by infrared spectra. With the ordering increasing, the charge amount storedin films which are stretched2times significantly increases. However, in the filmsstretched for4times, the stored charge amount’s changing with the orderingincreasing is not obvious. IR spectra prove that, not only relying on the porphyrin ring, the ordered porphyrin LB films can form head to head interactions, but also form theinteractions of end to end by hydroxyl, which principle affects the charge transfercharacteristics of the porphyrin films.The theoretical calculations show that, the carbon bonds length on porphyrin ringare all between the single and double bonds. Because of π bonding, porphyrin ring forthe overall is performance of conjugation characteristics. When the π bond is preparedorderly, it can effectively release and storage of electronic and has very highelectrochemical activity.