AGGREGATE FORMATION OF CROCETINDIALDEHYDE IN LANGMUIR-BLODGETT-FILM - A SPECTROSCOPIC STUDY

The miscibility of crocetindialdehyde (CDA) and stearic acid (SA) in air-water subphase has been studied from the surface pressure-area isotherms by using the surface phase rule and excess area criterion. Positive deviation from the additivity rule and positive values of Gibb's free energy indicate strong repulsive interaction between CDA and SA molecules. This repulsive interaction may facilitate aggregate formation of CDA in air-water subphase. CDA has been incorporated into Langmuir-Blodgett (LB) films when mixed with SA. Absorption and emission spectra of CDA have been studied in solution, in LB films, and in an ethanol-water mixture. The resemblence between the absorption spectrum of CDA in a ethanol-water mixture and in LB film supports aggregate formation of CDA. Dual fluorescence of CDA has been observed in solution and in LB films and for the first time in an organized molecular layer of a carotenoid. A comparison of emission and absorption spectra of CDA in solution and in LB films confirms formation of aggregates in LB films. The aggregate formation of carotenoids has been discussed in the framework of possible self-organization in biological membranes.