Fluorescence sensing

Fluorescence-based chemical sensors for explosive compounds, such as nitroaromatics and nitroalkanes, are a significant method of detection due to the sensitive and cost effective nature of this method. Current detection materials that rely on p -stacking interactions for fluorescence quenching of nitroaromatics are ineffective towards nitroalkanes. Nitroalkanes have a 3-D structure that does not easily p-stack and therefore interactions with these materials are difficult. Nitroalkanes also have unfavorable reduction potentials for electron transfer and also lack relevant electronic absorption to facilitate energy transfer. A well-designed sensor should be sensitive, able to detect a variety of analytes both aromatic and alphatic, and able to identify various classes of these compounds.

Zn(salicylaldimine) (ZnL) complexes are attractive candidates for fluorescence based sensing due to their high quantum yields, mixed dynamic and static quenching mechanism, and accessibility in both solution and solid state. We have observed fluorescence quenching with both nitroalkanes and nitroaromatics in solution by a photoinduced electron transfer. We have studied the quenching mechanism at varying concentrations using a family of ZnL complexes that structurally alter the reduction potentials. The solution state structure and dynamics have been characterized, showing a monomer-dimer equilibrium depending on the Lewis basicity of the solvent. In the solid state we have worked to vary stacking interactions to alter emission wavelengths as well as incorporate space for solvent incorporation. We are extending this work into solid state vapor phase quenching, as well as developing a method for identification of individual analytes.