Electron spin resonance characterization of Langmuir-Blodgett films containing functional molecules

The role of electron spin resonance (ESR) spectroscopy in the characterization of Langmuir-Blodgett (LB) films containing functional molecules is discussed. Unpaired electrons in LB films are associated with radical molecules produced by charge transfer, paramagnetic metallic ions such as CU2+ and so on. ESR parameters such as g-value and hyperfine coupling provide information of local molecular orientation and electronic states. ESR can unambiguously determine the orientation distribution function of molecules through g-value anisotropy. The case of mixed LB films of a merocyanine dye and arachidic acid is discussed as a typical example. The analysis of the anisotropic ESR spectra of stable radicals existing in these films has revealed detailed in-plane orientation of radicals, which led to the discovery of flow orientation effect during LB dipping process. Light-induced ESR (LESR) is introduced to directly detect the dye radicals generated by photoinduced charge transfer, Observed LESR spectra, associated with a resolved N-14 hyperfine structure, uniquely probe the orientation and electronic states of dye molecules forming the J-aggregates in highly ordered LB matrix. AFM observation of dye domains in these films is also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.