No abstract

Nickel and lead phthalocyanine (NiPc and PbPc) thin films prepared by vacuum sublimation have been investigated for use as gas sensors. High sensitivity (25 ppb), reversibility, and very fast response time (∼ seconds) have been demonstrated for detection of NO2 at room temperature. The sensor output increases by five to seven orders of magnitude as the gas concentration is increased from ∼2×101 to 6×104 ppb. Measurements of transient response characteristics versus gas concentration exhibited a simple logarithmic dependence. Application of this approach to the detection of other agents is discussed. It appears that the unique electrical properties of these films are a result of the film morphology associated with our specific deposition approach. Detection based on optical sensing of NO2 has also been demonstrated.

No abstract

No abstract

This contribution reports an integrated chemical and physicochemical study of the effects of halogen (I2, Br2) doping on the cofacially joined metallomacrocyclic polymers [M(Pc)O],. Resonance Raman and transmission infrared spectroscopy indicates the formation of ( [ M ( P c ) O ]~~~+ (~/ , I , -)~)~, M = Si, Ge, and ([Si(P~)o]y/~+(~/,Br,-)~), materials for y I 1.1. In contrast, for M = Sn, evidence is presented for the destruction of the tin-oxygen bonds upon doping. For M = Si and Ge,the transmission infrared spectra also reveal the progressive growth of electronic absorption with incremental doping; the effect is somewhat stronger for Si than for Ge. Transmission optical spectra of these materials reveal the formation of phthalocyanine x radical cation species and chains of 13-counterions. EPR spectra are also in accord with the ligand-centered P radical character of the halogen oxidation. Studies of the doping process (M = Si, Ge) by X-ray diffractometry indicate that it is inhomogeneous and that a single, limiting phase of stoichiometry y = 1.1 is produced upon halogenation. Structural characterization of the ( [S~(PC)O]I,,,~),, ( [G~(PC)O]I~,,~),, and ([S~(PC)O]B~,,,~), phases by computer analysis of the diffraction data (supported by judiciously selected model compounds) indicates architectural motifs that are essentially isomorphous with Ni(Pc)I, Le., stacks of staggered M(Pc) units and parallel chains of I,-counterions. The data can be indexed in space group P4/mcc, Z = 2, with a = 13.936 (6) A, c = 6.488 (3) A, phthalocyanine staggering angle = 39.5' (Ni); a = 13.97 ( 5 ) A, c = 6.60 (4) A, staggering angle = 39 (3)' (M = Si); a = 13.96 ( 5 ) A, c = 6.96 (4) A, staggering angle = 40 (4)' (M = Ge). Evidence is presented that the I,-(or Br,-) counterions are disordered along c. Variable-temperature static magnetic susceptibility studies of the ([M(Pc)O]I,), polymers reveal a small, sample-dependent Curie component and a Pauli-like, weakly temperature-dependent contribution. The magnitude of the latter is linearly proportional to y and can be associated with the fully doped, y 1.1 phase. The magnitude of the Pauli-like component increases with increasing interplanar ring-ring spacing (Ni -Si -Ge) while bandwidths ( 4 t ) calculated on the basis of a simple tight-binding model decrease. High-resolution 13C NMR spectra ('H decoupled with cross-polarization and magic angle spinning) reveal a downfield shift of [Si(Pc)O], carbon resonances upon doping. Optical reflectivity studies of the M = Si and Ge materials reveal the development of a plasma-like edge in the infrared upon incremental doping with iodine (the effect is stronger for Si than for Ge). Comparison of the data for Ni(Pc)I, ([Si(Pc)O] and ([Ge(Pc)O]I,,,,), reveals the progressive shift of the edge to lower energy with increasing interplanar spacing (Ni -Si -Ge). This trend is paralleled by plasma frequencies (w,) derived from a Drude analysis and tight-binding bandwidths calculated therefrom. Four-probe electrical conductivity measurements for poly...