AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP10
Reaction Site Selectivity of Analyte Gases on Metallophthalocyanines: A Density Functional Theory Study

Tuesday, November 1, 2005, 4:00 pm, Room Exhibit Hall C&D

Session: Surface Science Poster Session
Presenter: N.L. Tran, University of California at San Diego
Authors: N.L. Tran, University of California at San Diego
S.R. Bishop, University of California at San Diego
G.C. Poon, University of California at San Diego
A.C. Kummel, University of California at San Diego
Correspondent: Click to Email
Numerous studies have reported the use of metallophthalocyanines (MPcs) as thin film sensors for analyte gases, but a basic understanding of gas chemisorption onto these metal coordination complexes is lacking. Density functional theory was used to investigate the mechanism of chemisorption of two different analytes, NO and NH@sub 3@, onto two different MPcs, CoPc and FePc. Four analyte binding sites on the MPcs were investigated: (i) metal centers, (ii) inner ring nitrogen atoms, (iii) outer ring nitrogen atoms, and (iv) organic rings. For NO on FePc and CoPc, simulations show chemisorption onto the metal centers and physisorption onto the outer ring nitrogens and organic rings. In contrast, NH@sub 3@ chemisorbs onto the FePc metal center and physisorbs onto the Co metal. All other binding sites were not energetically favorable. Additionally, these calculations show a multi-step absorption mechanism in which NO initially binds to the inner ring nitrogens and then undergoes a barrierless migration to the deep chemisorption well on the metal centers for FePc and CoPc. PDOS simulations reveal that the binding of NO and NH@sub 3@ to the FePc metal center significantly alters the electronic structure of the clean FePc. However the two systems have opposite charge transfer mechanisms: charge is accepted by the NO chemisorbate from the Iron metal but is donated from the NH@sub 3@ chemisorbate to the Iron metal. These different charge transfer mechanisms will differentially affect charge relaxation times and the photoconductivity threshold in an MPc film and therefore can be used to identify analytes instead of just measuring analyte concentration. Additionally, simulations are being performed to study the possibility of subsurface diffusion of the NO molecule into the bulk.