Aggregate formation of crocetindialdehyde in Langmuir-Blodgett film: a spectroscopic study

Abstract

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 excess area criterion. Positive deviation from the additivity rule and positive values of Gibb's free enerty 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 incorporate 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 ethanol-water mixture and in LB films supports aggregates formation of CDA. Dual fluorscence 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 aggregate in LB films. The aggregates formation of carotenoids has been discussed in the framework of possible self-organization in biological membranes.