The novel amphiphilic benzodithia-18-crown-6 butadienyl dye (1) forms relatively stable insoluble monolayers on distilled water (collapse pressure of 41 mN/m) and on aqueous subphases containing alkali metal or heavy metal salts (collapse pressures in the range of 27-38 mN/m, respectively). The dye 1 monolayer organization depends on chromophore association and interactions (especially complex formation) with heavy and alkali metal ions as deduced from surface pressure-area and surface potential-area isotherms as well as reflection spectra and Brewster angle microscopy observations. Dye 1 undergoes specific interactions with Hg 2 + and Ag + , respectively (formation of different complexes). Nonspecific interactions have been observed with other salts, such as KClO 4 or Pb(ClO 4 ) 2 . Further, dye 1 monolayers on 1 mM Hg(ClO 4 ) 2 solution undergo reversible photoisomerization, in contrast to monolayers on water and other aqueous salt subphases.