CONTROL OF AGGREGATE FORMATION IN MEROCYANINE LANGMUIR-BLODGETT-FILMS

An H-like band, blue-shifted from an absorption maximum of a monomer b and, has been formed in merocyanine-arachidic acid mixed Langmuir-Blod gett (LB) films by adding n-alkane species of different chain lengths (CH3(CH2)(n-2)CH3, n=18 and 28) as a third component. In each ternary system, the blue-shifted band is prominent or is accompanied by a J-ba nd depending on the preparation conditions. The absorption spectra A(p arallel to) and A(perpendicular to) were measured using a normal incid ent of linearly polarized light with the electric vector either parall el or perpendicular to the dipping direction, respectively. The result s of surface pressure-area isotherm measurements have indicated that t he alkane species remaining in the monolayer and filling empty spaces near surface-active molecules act as the trigger molecules to induce t he H-like aggregates. Comparing these results with the predictions fro m the theory of flow orientation and the extended dipole model, it is suggested that the present blue-shifted H-like band is of an H-aggrega te rather than a dimer. (C) 1998 Elsevier Science S.A. All rights rese rved.