Surface plasmon resonance studies on Langmuir-Blodgett films of novel octa-substituted metal-free phthalocyanine molecules

The surface plasmon resonance technique is employed to characterize Langmuir-Blodgett (LB) films of novel amphiphilic octa-substituted metal-free phthalocyanine molecules. The refractive index n(c) is determined as a function of film thickness by fitting the experimental reflected intensity data to the exact Fresnel reflection formula. The angle of resonance is changed by about 0.33 degrees corresponding to a change in the phase velocity of 1.4 x 10(6) m s(-1) for each additional monolayer. A value of 1.6 for n(c) is believed to be reasonable in the light of data available for other phthalocyanine compounds. The monolayer thickness is estimated to be 1.7 nm and the molecular planes are believed to be stacked at an angle of 47.7 degrees to the substrate. The inner radiation arising from the LB coating of phthalocyanine molecules is found to be ten times greater than radiation damping, contributing significantly to the reduced depth of resonance.