Spectroscopic properties of merocyanine J‐aggregate in LB films

Langmuir–Blodgett (LB) films incorporating unsymmetrical merocyanine dyes; MC(X) (X = O, S, Se), have been fabricated. The J‐aggregates of MC(S) and MC(Se) are characterized by a sharp J‐band and resonance fluorescence. The MC(O) aggregate has a broad absorption band and is non‐fluorescent. We have examined the formation of mixed J‐aggregates in the MC(X)/MC(Y) assemblies (X, Y = O, S, Se). It has been found that a homogeneous aggregate of amalgamation type (HA‐aggregate) is formed in the MC(S)/ MC(Se) assembly. The mixed J‐aggregate in the MC(O)/MC(S) and the MC(O)/MC(Se) assemblies are classified into a mosaic (M‐)aggregate in a wide sense. Despite of similar molecular structure of MC(O) with both MC(S) and MC(Se), the growth of the MC(O) aggregate with a help of the J‐aggregate of MC(S) or MC(Se) as a template may hinder the homogeneous mixing of dye molecules. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)