Amorphous 1,4-dimethylnaphthalene, DMN, that can be prepared by vacuum deposition on Al2O3 exhibits relatively intense excimer fluorescence. Upon heating the surface, the adlayer undergoes a disorder-to-order transition, signaled by a decrease in excimer and an increase in monomer fluorescence. In a bilayer experiment, water, which has a lower desorption temperature than DMN, is vacuum deposited first, followed by DMN. When the surface is heated, water percolates through the DMN and forms a molecular H2O-DMN surface complex that desorbs simultaneously. The stoichiometric ratio of this complex was determined to be (DMN)(1.4 +/- 0.3)center dot H2O. When the bilayer was formed with p-xylene, a complex of DMN-p-xylene was observed that had the stoichiometry of (DMN)(7.9 +/- 1)center dot p-xylene.