SPECTROSCOPIC STUDY OF NONAMPHIPHILIC 9-PHENYLCARBAZOLE ASSEMBLED IN LANGMUIR-BLODGETT-FILMS

The monolayer characteristics of nonamphiphilic 9-phenylcarbazole (PCB ) mixed with stearic acid (SA) have been studied at the air-water inte rface. Miscibility studies as well as the Gibbs free energy measuremen ts indicate a repulsive type of interaction between the two component molecules in the mixture that results in the formation of aggregates o f PCB. Spectroscopic studies reveal that PCB in mixed LB films is high ly fluorescent and forms organized aggregates. The high-energy phospho rescence emission bands in an ethanol-glass matrix are quenched wherea s the low-energy bands are manifested in the LB films. This has been a ttributed to aggregation-induced reabsorption, which is unusual for si nglet-triplet transitions. The large difference in phosphorescence lif etime in two different microenvironments supports the formation of sma ll microcrystalline domains in LB films at 77 K. Scanning electron mic rographs clearly demonstrate the existence of such aggregates in the f ilms, and the size of the aggregates is in the range 0.1-4 mu m.