Immobilization of pyrene via diethylenetriamine on quartz plate surface for recognition of dicarboxylic acids

A novel photo-luminescence film has been prepared by immobilizing pyrene on a quartz plate surface via diethylenetriamine. Imino structure was intentionally introduced into the long flexible spacer due to their hydrogen bond forming abilities with carboxylic acids. It has been found that the film shows combined monomer and excimer emission of pyrene both in wet and dry states. Steady-state and time-resolved fluorescence emission measurements demonstrated that the excimer emission mainly came from direct excitation of ground state dimers, and/or monomers in aggregated state. The structures of the excimers formed during the excitation are mixtures of “standard excimers” and “distorted excimers” of the fluorophore moieties. Fluorescence lifetime measurements showed that the decay of the film is complex, and a four exponential fit is necessary for getting a satisfied result. The photophysical behavior of the present film could be rationalized by employing the model proposed before. Sensing property studies showed that the emission of the film is sensitive to the presence of dicarboxylic acids, including ethanedioic acid, malonic acid, etc. In contrast, presence of monocarboxylic acids, such as formic acid and acetic acid, had little effect upon the fluorescence emission of the film. Compared with the films taking ethylenediamine or 1,3-diaminopropane as their spacer component, introduction of diethylenetriamine into the spacer improved the performance of the film greatly. In addition, the sensing process is reversible, and the film is stable within a number of months provided it is properly preserved. These characteristics showed that the film is worthwhile for further exploration.