Multiphoton fluorescence quenching of conjugated polymers for TNT detection

The use of conjugated organic compounds in fluorescence sensing applications has been demonstrated to provide an impressive method to detect energetic nitro-aromatic compounds. The amplified fluorescence quenching in conjugated polymers was used for trace detection of nitro-aromatics. This method, under one-photon excitation, possesses certain limitations such as the use of harmful ultra-violet radiation and relatively high background noise from light scattering. A novel approach that utilizes the additional benefits of nonlinear optical methods involves multiphoton excited fluorescence. This technique employs infrared excitation which is essential for eye-safety applications and allows for deeper penetration through the atmosphere, with relatively low background noise. We herein report, two conjugated polymers which show good multiphoton absorption properties. This is combined with the excellent sensitivity of the multiphoton excited fluorescence to the presence of tri-nitro toluene (TNT). The multiphoton absorption cross-sections are provided and the Stern-Volmer plots are discussed. This technique, in combination with the great analyte sensitivity of various organic materials, promises to be an important sensing technology in the infrared spectral regions.