Monomolecular-layer assembly of oligothiophene on glass wafer surface and its fluorescence sensitization by formaldehyde vapor

A novel oligothiophene, specifically 2,2′:5′,2″-terthiophene (3T), functionalized film was fabricated by monomolecular layer assembly of 3T onto an amine-terminated glass wafer surface. Contact angle, XPS and steady-state fluorescence measurements demonstrated that the fluorophore was successfully immobilized on the substrate surface. The fluorescence emission of the film, however, is not stable in air, and it decreased along with increasing scanning number. Continuous irradiation of the film with UV light (365 nm) decreased, but stabilized the fluorescence emission of the film. Exposure of the specially treated film into formaldehyde (HCHO) vapor generated a new fluorescence emission, which appeared in a shorter wavelength in comparison with that of the original one. The intensity of the emission increased along with increasing the exposure time. Furthermore, interference experiments revealed that the sensitization is selective, and solvents including common acids, base and alcohols have little effect upon the process. More interestingly, the process is reversible. Accordingly, it is believed that the 3T functionalized film should be a strong candidate for developing a novel and sensitive HCHO fluorescent film sensor.