RESOLUTION OF THE EXCITED-STATES OF THE FLUORESCENCE PROBE TNS USING A TRILINEAR ANALYSIS TECHNIQUE

The technique of trilinear analysis was applied to characterize the st eady-state room-temperature fluorescence of the probe 2-(p-toluidino)n aphthalene-6-sulfonate (TNS) in various solvents. Our approach recogni zes that the fluorescence of a mixture of fluorophores is separately l inear in each of the independent variables of excitation wavelength, e mission wavelength, and probe concentration. We confirmed the sensitiv ity of TNS emission to solvent characteristics and resolved the contri butions of three distinct components to the overall TNS fluorescence s pectrum. Our results are consistent with the existence of three distin ct excited states and further demonstrate that the limitation of previ ous studies to a single excitation wavelength led to an incomplete cha racterization of TNS emission in aqueous solutions. TNS fluorescence i s attributed to emission from the conventional pi --> pi excited stat e with a nonplanar orientation of the phenyl and naphthalene rings, fr om a charge-transfer state with a coplanar arrangement of the ring sys tems, and from a charge-transfer state with a nonplanar ring orientati on induced by protonation of or hydrogen bonding to the bridging nitro gen atom.