Monomolecular layers of pyrene as a sensor to dicarboxylic acids

A novel photoinduced luminescence film has been prepared by immobilizing pyrene on a quartz plate surface via a flexible long spacer. The film shows combined monomer and excimer emission of pyrene both in wet and dry states, and the excimer may be formed mainly by direct excitation of ground-state dimers and/or monomers in aggregates. Classical Birks' scheme plays a little role in the formation of the excimers. The emission of the film is sensitive,to the presence of dicarboxylic acids, including ethanedioic acid, malonic acid, succinic acid, etc. The emission in the monomer and excimer region increases with addition of the acids. The time needed for the emission to reach equilibrium depends on the nature of the acids. It has been shown that the longer the chains of the acids, the more 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. Experimental results from similar studies using formic acid and acetic acid are in support of this explanation. Furthermore, the response of the film to dicarboxylic acids is reversible.