INFLUENCE OF THE PHASE STATE OF PHOSPHATIDYLCHOLINE MATRIX MONOLAYERSON THE PHOTOPHYSICAL CHARACTERISTICS OF AN AMPHIPHILIC OXACYANINE DYEAT THE AIR-WATER-INTERFACE

The photophysical characteristics of an amphiphilic oxacyanine dye emb edded in phospholipid matrix monolayers at the air/water interface are reported. The matrix molecule used in the present study was dimyristo yl phosphatidyl-choline. Surface pressure-, reflection- and fluorescen ce- area isotherms along with fluorescence and reflection spectra were measured as a function of dye/lipid molar ratio and subphase temperat ure. It is observed that the photophysical properties of oxacyanine dy e depend sensitively on the molecular organization parameters of the m atrix monolayer. The surface density normalized fluorescence intensity shows a strong increase with increasing surface pressure. The reflect ion-area isotherms along with the reflection spectra show no evidence of dimer formation up to a dye/lipid molar ratio of 1:5. Further incre ase of dye concentration leads to changes in reflection spectra indica ting dimer and higher aggregate formation. The fluorescence intensity varies linearly with dye concentration up to a dye/lipid molar ratio o f 1:50. The fluorescence quantum yield increases strongly with decreas ing temperature (275-300 K) of the subphase. The dependence of photoph ysical properties of the dye on various molecular organization paramet ers is discussed in terms of phase transitions and fluidity of the mat rix monolayer.