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 Hg2+ and Ag+, respectively (formation of different complexes). Nonspecific interactions have been observed with other salts, such as KClO4 or Pb(ClO4)(2). Further, dye 1 monolayers on 1 mM Hg(ClO4)(2) solution undergo reversible photoisomerization, in contrast to monolayers on water and other aqueous salt subphases. (C) 2003 Elsevier Inc. All rights reserved.