Characterization of interfacial effects in organic macrocycles Langmuir and Langmuir–Blodgett layers studied by surface potential and FT–IR spectroscopy examination

Abstract

Surface potential (SP) examination and FT–IR (infrared) reflection–absorption spectra were used for the characterization of interfacial effects in organic dye thin layer on solid substrates. Surface potentials of magnesium tetranaphtylporphyrin (MgTNP), magnesium or lead phthalocyanine monolayer on the water subphase were measured and the dipole moments of the investigated dyes were evaluated (1.07 D, 0.52 D and 0.31 D for MgTNP, MgPc and PbPc, respectively). The differences between the dipolar moment values were attributed to the differences between porphyrin and phthalocyanines molecular structures and to the differences in metal electronegativity and metal ion distortion in the molecular frame. Also asymmetry in the covalent linkage and coordination bonding in the center of the molecular skeleton and the differences in polarisablility of the dye molecules as sources of the difference in the dipolar moment values were taken into consideration. The FT–IR reflection–absorption spectra were used for the characterization of the magnesium phthalocyanines Langmuir–Blodgett (LB) layer formed on semiconducting (In 2O 3) or Au substrates. The modification of the IR spectra upon Langmuir–Blodgett dye layer deposition was attributed to the redistribution of electrons at the semiconducting (metallic)/dye layer interface and to different substrate morphology. The difference in the band splitting for dye on Au and In 2O 3 was related to the smaller amount of charge transferred to the dye film from In 2O 3 than from Au substrate and to the changes in the topology of the different substrates after coating with the dye layer.