Electron affinity of adsorbed dye monolayers

Abstract

We have calculated the electron affinity of dye molecules and compared it with experimental results from the electron beam retardation method. The calculations were performed on the dye pinacyanol adsorbed on CdS. First, we calculated the single molecule electron affinity which corresponds to the vapour state electron affinity. Next, we calculated the electron affinity of a molecule in a linear aggregate, considering the neighbouring molecules, and finally, the electron affinity of molecules in aggregates adsorbed on an ideal crystal substrate and on a substrate with defects. We prove that there is a distribution of electron affinities which is caused by random defects on the substrate surface. The experimental electron affinity for monolayers of pinacyanol on CdS corresponds to the highest electron affinities in the distribution. We propose that this is caused by electron diffusion in the dye, and present additional experimental evidence which supports our conclusion. The effects of various interactions are evaluated ; these are nearly independent of the SCF-LCAO method used, since they are found by taking the difference of two calculations. These results are compared with the corresponding ionization energies, which have been verified by photoionization experiments.