UV/vis spectroscopy of metalloporphyrin and metallophthalocyanine monolayers self-assembled on ultrathin gold films

The use of evaporated ultrathin gold films on mica to obtain transmission U V/vis spectra of monomolecular overlayers containing chromophores is demons trated. The gold substrates (thickness, 13-100 Angstrom) were studied by sc anning force microscopy. UV/vis spectroscopy, and X-ray diffraction and fou nd to exhibit an array of {111} textured islands, whose sizes and optical p roperties can be controlled by the evaporation conditions and subsequent an nealing. The use of gold substrates of this kind enables one to clearly res olve UV/vis absorption spectra of (sub)monolayers. This methodology is appl ied to the study of the binding of cobalt and iron tetraphenylporphyrins (C oTPP and FeTPPCl, respectively) and cobalt phthalocyanine (CoPc) to various N-donor ligand monolayers, self-assembled on ultrathin Sold films. Enhance ment of the gold surface plasmon absorption, resulting from molecular self- assembly on the gold island film, is used to semiquantitatively follow porp hyrin binding to the monolayer.