Studies on the photochemical stabilities of some fluorescent films based on pyrene and pyrenyl derivatives

• The photochemical stability of a number of pyrene and pyrenyl derivatives-based fluorescent films was studied systematically.
• Mechanism studies revealed that photochemically the pyrene and pyrenyl derivatives-based films decomposed via two channels.
• 1H NMR, FTIR and high-resolution MS studies revealed that ring-opening and oxidation of the saturated carbon next to pyrenyl structure are two of the important results of the photochemical degradation of the fluorophores tested.

Photo-degradation is one of the most challenging problems to limit the re-usability of fluorescent film sensors, and thereby, it is a necessity to evaluate the photochemical stability of a fluorescent film before it is put into practical uses. Accordingly, the photochemical stability of some widely used pyrene and its derivatives-based fluorescent films were studied under mild conditions (i.e., in air and at room temperature) with ultraviolet (UV) or visible light as the light source. It was found that the fluorophores based films fabricated in physical ways are all un-stable to the irritation of light, in particular when UV is employed as a light source. 1H NMR, FTIR and high-resolution MS studies revealed that ring-opening and oxidation of the saturated carbon next to pyrenyl structure are two of the important results of the photochemical degradation of the fluorophores tested. But it is to be noted that photo-chemically pyrene is much more stable than its derivatives no matter what kind of substituent is introduced. Furthermore, the films are only sensitive to the illumination of UV light rather than visible light. Mechanism studies revealed that the pyrene and pyrene derivatives-based films decomposed via two channels under light irritation. One is the photo-decomposition without the participation of other chemicals, and the other is photo-degradation via reaction with the chemicals. Kinetic study demonstrated that the films lost their fluorescence mainly via the second channel. It is believed that this finding is of interest to the development of novel pyrenyl derivatives-based fluorescent film sensors.

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