| Fluorescence and fluorescence polarization were used both independently and in conjunction with electrochemical experiments to study species deposited on surfaces. Metal-free and zinc tetraphenylporphyrin and ruthenium tris(bipyridine) were deposited onto glass, single crystal silicon and electrodes of indium oxide coated glass, pyrolytic graphite and thin gold films. Deposition was accomplished by (a) drying an aliquot of solution that had been loaded by syringe, (b) dipcoating from solution, (c) spincoating a polymeric solution or (d) vacuum deposition.;A theoretical treatment of the polarization of fluorescence from species on a surface was developed for several ideal cases. For transitions parallel to the surface, as the angle of incidence is varied from 0(DEGREES) to 90(DEGREES), the polarization decreases from 1.0 to a final value which depends on the absorption and emission transitions--0.5 for linear oscillators parallel to each other, -0.5 for linear oscillators perpendicular to each other and 0.0 for planar oscillators. For planar oscillators oriented normal to the surface, the polarization ranges from -0.33 to 0.0. Interferences caused by substrate heterogeneity and differences in refractive index are discussed.;The fluorescence polarization for desposits on glass decreases from between 0.2 and 0.3 to 0.0, suggesting parallel orientation to some extent. For thin layers of either TPPs or Ru(bpy)(,3)('2+) on Si, the polarization changes from -0.6 to 0.0. A model is proposed in which transitions parallel to the surface are selectively quenched in that portion of the deposit close to the surface.;On graphite electrodes, only 1% of the molecules in a dipcoated deposit of ZnTPP are electroactive, but oxidation results in strong quenching of luminescence from the deposit. The excitation spectrum of the luminescence on graphite, gold or silicon at low coverages features a very weak contribution from the Soret transition; this transition reappears with heavier coverages of increasing distance from the surface. On indium oxide, the degree of electroactivity is higher, and similar degrees of quenching can be obtained upon oxidation, but there are no unusual spectral modifications in thin layers. A model for the structure of ZnTPP deposits is proposed on the basis of these observations. |
