DISKOTIC MULTIYNE LANGMUIR-BLODGETT-FILMS .2. AGGREGATE AND MONOMER UV-VIS ABSORPTION AND FLUORESCENCE

Absorption and fluorescence spectra of a new multiyne diskotic compound is studied in thin films and solutions. A detailed energy diagram of the monomer absorption transitions is derived. A correlation between the structural organization of the diskotic Langmuir-Blodgett films, characterized in part 1, and their optical properties is found. The significance of the pi-pi interactions in determining the type of the molecular aggregation is illustrated for the disk-shaped aromatic compounds considered in part 1. A set of rules are deduced on the basis of the electrostatic theory of the pi-pi interactions to predict the preferred type of diskotic liquid-crystalline phases depending on the molecular peculiarities and arrangement. The effect of the intra- and interlayer molecular aggregation, environment and ct-electron interactions on the optical properties of the diskotic films is discussed. The preferential orientations of the main transitional dipoles is determined using polarized absorption. The red shift of the J-aggregate bands evidence the nematic arrangement of the disk-like molecules in the monolayers. Anomalous fluorescence with quantum yield of 0.36 is found.