MULTILAYER FILMS OF CHROMOPHORIC CELLULOSE OCTADECANOATES STUDIED BY FLUORESCENCE SPECTROSCOPY

Multilayer films of pyrene-labeled cellulose octadecanoate were investigated by fluorescence spectroscopy. Cellulose trioctadecanoate forms a homogeneous monolayer at the air/water interface. The surface pressure (pi)-area (A) isotherms indicate that the introduction of pyrenyl groups as much as 7% (by side chain mole base) does not essentially alter the monolayer characteristics. The monolayer on the water surface was transferred successfully onto a substrate by a horizontal lifting method to form a Y-type multilayer film. The fluorescent properties (fluorescence spectrum and decay curve) were independent of the number of layers, which suggests no interlayer excimer formation and no interlayer energy transfer. Analysis of the fluorescent quenching efficiency as a function of pyrenyl content revealed that the pyrenyl groups are two-dimensionally randomly distributed within each layer. Furthermore, in the multilayer film with high pyrenyl concentration, the formation of two types of excimers was demonstrated by time-resolved fluorescence spectroscopy. One is a sandwich excimer and the other is a partially overlapped one. The existence of the latter excimer means that the conformational change of side chains in such a system with a condensed structure is appreciably restricted.