Studies On The Sensing Films For Dicarboxylic Acids Based On Molecular Recognition

In recent years, monomolecular assemblies on solid surfaces have attracted growing attention due to their potential application in creation of novel electronic, photo-electronic and sensing films. Chemical immobilization of small molecules onto substrate surface is one of the important approaches to prepare monomolecular assemblies and provides a convenient way to produce surfaces with specific chemical functionalities that allow the precise turning of surface properties. The properties of the modified surfaces depend upon a number of factors, including, at least, the nature of the small molecules, the properties of the substrate surface, the structure of the spacer, which links the small molecule and the substrate, and the density of the small molecules on the substrate surface. Clearly, a variety of functional films with ideal properties may be prepared by careful selection and combination of the small molecules, the substrate and the spacer.Based upon this methodology, a number of functional films with pyrene (Py) as a fluorescence active molecule have been prepared and studied as sensing materials in our laboratory. It has been demonstrated that the intensity and/or the profile of the fluorescence emission of the films are sensitive to the purity of water, the presence of nitrite in aqueous phase, and nitromethane in methanol, ethanol or water. Simple embedding of Py into chitosan (CS) film results in a medium polarity sensitive film. It is to be noted that all the sensing films reported from our laboratory have been designed with short or even no spacer, and the sensing principles of the films are based on the hydrophobic aggregation of the sensing element, Py, and its dependence on the presence of analytes.Based on the above-mentioned research works and the concepts of molecular recognition, imino units were intentionally introduced into a spacer, via which Py was immobilized on a substrate surface. Imino units were chosen due to its character to form hydrogen bond with carboxyhydroxy group. It was expected that the specific interaction of the imino group with carboxyhydroxy group would result in insertion of dicarboxylic acids into the space between neighboring spacers, altering the spatial distribution of the sensing element, Py, and thereby changing the photophysical behaviors of it. In thisdissertation, three films with different linker structures were designed and prepared. The photophysical behavior and sensing properties of the films have been studied using various steady-state and time-resolved fluorescence techniques.First, a novel photo-induced luminescence film has been prepared by immobilizing pyrene on quartz plate surface via flexible long spacer, ethylenediamine and 3-glycidoxypropyltrimethoxysilane. The film shows combined monomer and excimer emission of pyrene both in wet and dry states, and the excimer emission is mainly from ground state dimers, including both "sandwich" like and partially overlapped structures. The emission of the film is sensitive to the presence of dicarboxylic acids. The emission in the monomer and excimer region increases along with addition of the acids. The time needed for the emission to reach equilibrium depends upon the nature of the acids. It has been shown that the longer of the chains of the acids, the longer of the time is needed. This observation is explained by considering the conformational reorganization of the immobilized pyrene due to insertion of the dicarboxylic acids into the space between neighboring spacers.Considering the long responsive time of the film to dicarboxylic acids, we increase the length of the spacer and try to obtain another better sensing film. Using 1, 3-dianinopropane to replace ethylenediamine, we prepared another film. It is observed that the sensitivity of the film to dicarboxtlic acids is significantly improved, even though the photophysical behaviors of the new film is similar to the original one.In the third part of this dissertation, diethylenetriamine was employed to prepare a similar film. It is expected...