NAPHTHALENE CHROMOPHORE TETHERED IN THE CONSTRAINED ENVIRONMENT OF A SELF-ASSEMBLED MONOLAYER

[11-(2-Naphthyl)undecyl] trichlorosilane and octadecyltrichlorosilane were coadsorbed from hexadecane solution onto quartz. The absorbance ratio of the A-B(b) to A-L(a) transitions of naphthalene in the UV spectra of a monolayer compared to solution spectra indicate an orientation of the naphthalene chromophore with its long axis toward the normal of the substrate surface. Contact angles, transmission FTIR, and fluorescence spectra of adsorbed monolayers with different ratios of the two components show that the distribution of chromophores is homogeneous over the whole range of composition. The exclusive appearance of a high-energy naphthalene excimer with increasing surface concentration of the naphthalene-tagged component is observed and explained by the special geometry in the monolayer. A simple two-dimensional lattice model taking energy migration into account has been applied to explain the dependence of the ratio of excimer to monomer fluorescence on the surface concentration of naphthalene chromophores.