Preparation and sensing performance to formaldehyde vapor of quaterthiophene-based fluorescent films

A fluorescent film was fabricated by chemical immobilization of 2, 2':5', 2″:5″, 2″'-quaterthiophene(4T), which was employed as a sensing element, onto an amine-terminated glass wafer surface. It has been demonstrated that the fluorescence emission of the film is not stable in air, and it decreases along with increasing scanning time. However, the emission can be stabilized by treatment of the film under UV light irradiation in air. It was found with interesting that a new emission(λ_em=464 nm) appears after divulging the film in formaldehyde vapor. The intensity of the emission increases along with increasing the exposure time. Further experiments reveale that the fluorescence sensitization is fully reversible and highly selective. Common acids, ammonia and alcohols have little effect upon the fluorescent emission of the film. Therefore, it is anticipated that the film may be developed into a formaldehyde sensor. In addition, a possible sensing mechanism was proposed according to known photochemistry of oligothiophene and the experimental results from present study.