Langmuir−Blodgett Films of Bis(octakispropyloxy) Samarium Bisphthalocyanine. Spectroscopic and Gas-Sensing Properties

Abstract

In this work, the synthesis of a novel substituted bisphthalocyanine, the bis[octakis(propyloxy)phthalocyaninato] samarium(III) complex, is reported. Langmuir−Blodgett (LB) films of this compound have been prepared. The influence of the propyloxy groups in the structure of the LB films and in their spectroscopic, chemical, electrochromic, and gas-sensing properties has been evaluated. The π−A isotherms exhibit greater monolayer stability than that observed in the unsubstituted analogue. The compressed monolayers are easily transferred by Y-type deposition resulting in red films instead of the expected green monolayers. The LB films have been characterized spectroscopically using UV−vis, near-IR, and FTIR techniques. The UV−vis spectra show that the Q-band splits into two peaks on passing from the chloroform solution to the LB films. This is the first example of a Davydov splitting in a bisphthalocyanine compound. The Davydov splitting, which is responsible for the red color of the LB films, is characteristic of crystalline order. The FTIR spectra also indicate the presence of long-range order in the LB films. Electrochromism is clearly observed in cast films but appears attenuated in LB films due to the coincidence of the electronic absorption bands of the blue and red forms with the bands corresponding to the Davydov splitting. Finally, LB films deposited onto ITO microelectrodes (spacing of 75 microns) show an appreciable conductivity. The resistance of the devices varies reversibly when they are exposed to several volatile organic compounds. Although the resistance of the LB films is higher than that observed in similar gas sensors prepared from unsubstituted or tertbutyl-substituted bisphthalocyanines, the response toward the vapors is more intense.