Spectroscopic and gas adsorption properties of thulium bisphthalocyanine Langmuir-Blodgett films

Abstract

Langmuir monolayers of thulium bisphthalocyanine (TmPc 2) were formed on a water subphase with a well defined π-A isotherm and Langmuir-Blodgett (LB) films were fabricated on solid substrates. The spectroscopy of the material and LB films, UV-visible, near-infrared, infrared, Raman, resonance Raman, and surface enhanced Raman scattering, is presented. The tilted molecular orientation of the TmPc 2 molecules in the floating layer, indicated by the limiting area of the π-A isotherm, is also confirmed in the LB films by transmission and reflection-absorption infrared spectroscopy (RAIRS). The characterization includes the assignment of characteristic vibrational frequencies observed in the Raman and infrared spectra. The adsorption of NO x (NO 2/N 2O 4) gas on a bilayer LB film of TmPc 2 has also been studied. The LB film was deposited onto an interdigitated gold electrode and the absorption-desorption process was monitored by the change in electrical conductivity during exposure to NO x gas seeded in N 2. The thermal conductivity of the molecular semiconductor and the kinetics of the gas absorption and desorption processes at different temperatures have been investigated.