Langmuir-Blodgett films of Cu(II)-tetrakis(3,3-dimethylbutoxycarbonyl)phthalocyanine: A spectrophotometric and TEM analysis of their structure and morphology

Langmuir-Blodgett (LB) films of copper(II)-tetrakis(3,3-dimethylbutoxycarbonyl)phthalocyanine [Cu(dmbc)Pc] have been prepared from toluene solutions; multilayers (up to 80 layers) were deposited onto hydrophobic quartz substrates. The refractive index n and extinction coefficient k at normal incidence have been determined from both transmission and reflection measurements carried out in the 400-800 nm spectral range. The optical absorption spectrum as a function of the incident photon energy was also registered in order to determine the optical transition type in Cu(dmbc)Pc LB films by using a band model approach. Linearly polarised light absorbance measurements were performed at room temperature in the same spectral range. The average orientation of the phthalocyanine molecular rings in the LB film, with respect to the normal to the substrate and the dipping direction, has been evaluated. We have found that such orientation differs from that determined for LB films deposited from ethyl acetate solutions. Structural and morphological analysis were also carried out by transmission electron microscopy techniques. Small ordered domains in a low range order matrix were observed by high resolution images. The structure of the material in the substrate plane has been determined by electron diffraction performed on single ordered domains.