EXCIMER FORMATION AND EXCITATION-ENERGY TRANSFER IN LANGMUIR-BLODGETT-FILMS OF CELLULOSE DERIVATIVES CONTAINING CARBAZOLE

Fluorescence emission spectra are recorded for Langmuir-Blodgett (LB) films prepared from cellulose derivatives containing carbazole as a si dechain substituent. Three samples of differing carbazole content are considered. At low carbazole content, only the fluorescence characteri stic of monomeric carbazole emission is observed. Clear excimer emissi on is, however, evident in the spectra of the more highly substituted derivatives. Since similar excimer formation is not observed in soluti ons or cast films of the same polymers, it is concluded that molecular ordering in the LB films favours the parallel alignment of chromophor e units. For a given polymer of sufficiently high carbazole content, t he relative intensity of the excimer emission increases with the numbe r of transferred layers, indicating the interaction of chromophores in neighbouring layers. Energy transfer between layers is also evident i n experiments involving multilayer assemblies composed of a monolayer of 1-pyrenedodecanoic acid, covered with a varying number of layers of the carbazole-containing polymer; Excitation of carbazole results in strong emission from pyrene, whereas only weak emission is observed fr om carbazole. Ii is therefore concluded that energy transfer from carb azole to pyrene occurs in these LB films.