Distribution of Ionization Energies of TCC and TDC Molecular Surfaces

Abstract

We have measured the ionization energy of multimolecular overlayers of dyes on glass. The experimental and theoretical results on the position of the energy levels of the sensitizer dye molecules used, thiacarbocyanine (TCC) and thiadicarbocyanine (TDC), show that the ionization energy of the surface molecules is displaced by their interaction with equivalent point charges in their neighborhood. Such charged sites exist not only on crystalline and amorphous substrates, but also on molecular crystal surfaces. We have extended our earlier calculations for adsorbed molecules of pinacyanole on polycrystalline substrates to molecular layers of TCC and TDC. The results are interpreted in terms of the density of charged defects, the geometry of the external molecular layer and the effective distance of the molecular “ionization center” from the surface.