||Several organic-inorganic hybrid layer-by-layer self-assembled multilayer films and their conversion to functional films by various methods were developed for two application objectives: high performance multi-purpose electrochemical sensing to detect biologically important redox-active species and electrochromic coating materials. Chapter 1 is a brief introduction to the background and the current hotspots of layer-by-layer self-assembly method closely related to the main objectives of this thesis, including the assembly principle, characterization methods and specific applications. Chapter 2 describes the self-assembly of layer-by-layer molecular films with viologen (and viologen-derivatives) and heteropoly oxometalate on various substrates (e.g. glassy carbon, ITO) by alternatively dipping the substrates in anionic and cationic species. Electrochemical method, UV-Vis and FT-IR spectroscopies were employed to characterize the multilayer films. The successful applications of newly developed films in bifunctional electrochemical sensing of H2O2/ascorbic acid and O2/NO are demonstrated. Chapter 3 presents the fabrication of layer-by-layer self-assembled multilayer molecular films with viologen (and viologen-derivatives) and heteropoly oxometalate and their application in electrochromism. The assembly process was monitored by electrochemical method, UV-Vis and FT-IR spectroscopies. Spectroelectrochemistry, which couples the UV-Vis absorption with electrochemistry, was employed to study the reversible electrochromic behavior of the multilayer films. Chapter 4 reports the preparation, characterization of hybrid films containing metalloporphyrins and metal nanoparticles converted from self-assembled multilayer films and their applications in biosensing. UV-Vis spectroscopy, AFM, XPS and electrochemical method were employed to characterize the films. The electrocatalytic behaviors of the films were studied in detail, including catalytic reduction of oxygen and catalytic oxidation of nitric oxide. Chapter 5 focuses on a novel method to fabricate hybrid films containing metalloporphyrins and bimetallic nanoparticles by electrochemical or photochemical conversion of layer-by-layer assembled multilayer films. The assembling process and hybrid films were characterized by UV-Vis spectroscopy, electrochemical method, XPS, SEM and ICP-MS. The bimetallic nanoparticles can serve as catalysts in bifunctional sensing of O2 and NO. Chapter 6 demonstrates a novel method to prepare three-dimensional fractal Au nanostructure by its electrodeposition on polycation/polyanion multilayer films fabricated by layer-by-layer assembly. The fractal nanostructures were characterized by UV-Vis spectroscopy, SEM, AFM, XPS and electrochemical methods. The electrode modified with Au fractal nanostructures exhibits very high electrocatalytic activity towards the oxidation of NO. Chapter 7 summarizes the major findings of this thesis and outlines my personal perspective for this project on the basis of my research experiences and thinkings.