A class of fluorescent films in which pyrene was assembled, in a monolayer manner, on glass slide surfaces via various flexible spacers of different lengths and substructures was used for the detection of nitroaromatic compounds (NACs) in vapor phase. This design strategy offers several advantages for thin film fluorescent sensory materials. These advantages have been demonstrated experimentally by the sensitive response of the films to the presence of trace amounts of NACs in vapor phase. The fluorescence quenching of the films upon exposure to NACs vapors depends on several factors, including the evaporate rate of the NAC detected, the length of the spacers connecting the sensing element and the substrate surface, and the density of the sensing element on the substrate surface. Further experimentation showed that the sensing process is reversible and free of commonly encountered interference. The sensitive response, reversibility of the sensing process, and freedom from commonly encountered interference of the specially designed films to NACs qualify these materials as promising NACs fluorescent sensory materials.
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.
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