AGGREGATION-INDUCED REABSORPTION OF P-QUATERPHENYL ASSEMBLED IN LANGMUIR-BLODGETT-FILMS - A FLUORESCENCE STUDY

Nonamphiphilic p-quaterphenyl (QP) molecules mixed with stearic acid (SA) form highly stable monolayers at the air-water interface that may be transferred on to solid substrates as Langmuir-Blodgett (LB) films. The surface pressure versus area per molecule isotherms indicate that the QP molecules stand almost vertically at the air-water interface. The plot of the average area per molecule of the mixed system versus the molar concentration of QP as well as the Gibbs free energy measurements of the mixed films at the air-water interface indicate a repulsive type of interaction between the SA and QP molecules that simulates the formation of aggregates. Spectroscopic studies of QP in the LB films and in the binary mixture of ethanol and water are similar and indicate strong reabsorption effects. Moreover, the manifestation of the weak (l)L(b) bands in the excitation spectra of the LB films as well as in the binary mixture of ethanol and water has been attributed to the formation of organized aggregates of QP.