Study on the structural properties of merocyanine dye Langmuir-Blodgett films using electron spin resonance spectroscopy

Optical absorption and fluorescence as well as ESR measurements were performed on LB films of binary mixtures of four kinds of merocyanine dyes [DO], [DS], [DSe] and [6Me-DS], where [DS] and [DSe] form J-like aggregates but not [DO] in single component films. The observed optical absorption spectra of mixed films were markedly dependent on the combination of dyes. In [6Me-DS]-[DO] system, a sharp J-band peak linearly shifts to the longer wavelength for replacement of 6Me-Ds by DO. In the [DS]-[DO] system, [DS]:[DO]=1:1 film shows a both sharp J-band absorption and fluorescence peak In particular, [DS]_0.5[DO]_0.5 films show a sharp J-like absorption and a sharp J-band fluorescence peak with a small Stokes shift is observed. These results suggest that most DO molecules associate to form J-like aggregates in [DS]_1-x[DO]_x system. The role of ESR spectroscopy in the characterization of functional LB films is discussed. In structural studies, ESR is of particular importance in the analysis of molecular orientation of LB films. ESR can unambiguously determine the orientation of molecules through g-value anisotropy