Size and molecular configuration of dye aggregates in mixed Langmuir-Blodgett films based on merocyanine dye

We have studied the blue-shifted and the red-shifted bands formed in mixed Langmuir-Blodgett films of the merocyanine dye (MS)-arachidic acid (C-20)-n-octadecane (AL(18)) ternary system with the molar mixing ratio [MS]:[C-20]:[AL(18)]=1:2:x(0.5 less than or equal to x less than or equal to 5.0). The formation of the blue-shifted and the red-shifted bands depends on the AL(18) content, and shows that the aggregation state can be modulated by changing the AL(18) content. The observed overlapping spectra of the blue-shifted and the red-shifted bands are deconvoluted into two original bands. The extended dipole model has been applied to examine the aggregation state of MS referring to the deconvoluted spectra. Thus the estimated minimum aggregation number N-min and the slip angle alpha between the long axis of the aggregate and the transition dipole moment are N-min=40 and alpha=30 degrees and N-min=40 and alpha=50 degrees for fully-developed J- and H-aggregates, respectively, seen for x less than or equal to 1.5, and N-min tends to decrease with increasing x. (C) 2000 American Institute of Physics. [S0021-8979(00)01422-5].