The fluorescence quenching behavior of thin films of poly[1-(trimethylsilyl)phenyl-2-phenylacetylene] (PTMSDPA) was investigated for the purpose of application of this polymer to mono-and multicolor FL imaging. When the film was exposed to 365-nm UV light with a power of 18.6 mW/cm(2) in air at room temperature, the fluorescence band with a maximum at 530 nm rapidly decreased, and then finely resolved fluorescent images were easily obtained using photomasks. After a prolonged irradiation time of 30 min, the PTMSDPA film exhibited an IR absorption peak at 1650 cm(-1) due to the carbonyl group. On this basis, we presumed that the fluorescence quenching reaction was due to a small amount of diradical formed initially upon UV irradiation. The fluorescence of the PTMSDPA film was little quenched under an irradiance less than 1.15 MW/cm(2) even for tens of minutes, whereas the fluorescence of a highly photosensitive dye, such as Nile red, was readily quenched because of the high polarity in the excited state. As a result, the Nile-red-dispersed PTMSDPA film provided multicolor fluorescent images upon an irradiance of 1.15 mW/cm(2). The portions exposed through the photomask appeared the yellowish-green color of PTMSDPA, whereas the protected portions were the reddish-orange color of Nile red.