Optical studies of organized dye multilayers

Abstract

The optical studies of organized dye multilayers constructed by the Langmuir- Blodgett technique are described. A number of different organic dye materials are examined; and some warrant special attention. They are S120 a cyanine, the squaraines and perylene. It is shown that these dyes form particularly well ordered films with unique optical properties. S120 forms J-aggregates, Sql and Sq3 both squaraines form hypsochromicaly shifted complexes (possibly H-aggregates) and Sq2 another squaraine exhibits band splitting (possibly Davydov). Fluorescence studies of perylene:tricosanoic acid films show that monomer and dimer species exist at room temperature, whilst at low temperature a third emitter is observed (excimer).Structural studies of perylene:tricosanoic acid films reveal a high degree of order. From the isotherms and polarized absorption spectra it is seen that the molecules are on their edges, tilted with respect to the substrate. RHEED measurements confirm the high degree of structural order. The dependence of surface plasmon resonance on the overlayers is demonstrated. The silver thickness and history are shown to be important in subsequent surface plasmon resonance measurements. An overlayer containing a dye with a sharp intense absorption band can interact with the surface plasmons to give anomalous dispersion (backbending). Only single backbending is observed for 8120 and Sql, indicating anisotropic films. Good agreement is found between 8120 backbending and data reported in the literature.