Fabrication and characterization of dicyanopyrazine-linked porphyrin Langmuir-Blodgett films

Abstract

Porphyrin is a heterocyclic macrocycle comprised of four pyrrole subunits linked through methane bridges. Unique properties of the porphyrin can be achieved by the introduction of functional groups such as electrochemically or photochemically active molecules. Porphyrin and its derivatives have recently received much attention because of their potential applications in photosensitizers, photodynamic therapy, photovoltaic cells, and optical sensors. One important consideration in such applications is the possibility of forming the organic compounds into thin films. The Langmuir-Blodgett (LB) technique is one of the most popular methods for fabricating molecularly assembled thin films on solid substrates with well-defined molecular orientation and well-ordered layer structures. This technique is useful for not only fabricating monomer films but also polymer films on various solid substrates such as glass, chromium, quartz, and silicon. In this work, we have fabricated dicyanopyrazine-linked porphyrin mono and multilayer films on polycrystalline gold and quartz substrates using the Langmuir-Blodgett (LB) technique. X-ray photoelectron spectroscopy (XPS) has been used to analyze the structural compositions of dicyanopyrazine-linked porphyrin LB films. Ultraviolet photoelectron spectroscopy (UPS) has been used to compare the valence electronic states between the porphyrin monolayer and multilayer LB films. Atomic force microscopy (AFM) and contact angle measurement have been used to analyze the surface morphology of the LB films, and ellipsometry has been used to measure the thickness of the LB films.