M. J. Cook

THE EFFECT OF NO2 ON OPTICAL ABSORPTION IN LANGMUIR-BLODGETT FILMS OF OCTA-SUBSTITUTED AMPHIPHILIC COPPER PHTHALOCYANINE MOLECULES

Thin films consisting of 20 layers of 1,4-bis(4-hydroxybutyl)-8,11,15,18,22,25-hexakisdecyl phthalocyaninato copper (CuAmPc) molecules have been deposited onto pre-cleaned glass slides by the Langmuir-Blodgett (LB) technique. The optical absorption of these films were studied in the range 1.4-4.0 eV in air and also in the presence of NO2 gas at 100 ppm level. Prolonged exposures have resulted in dramatic changes in the visible absorption band with the consequence of disappearance of Davydov splitting. Such effects are caused by the domination of local interaction between the central metal atoms and NO2 molecules resulting in a distorted herring-bone structure. This leads to the broadening of the energy levels a(2u) and e(g). Gas adsorption and desorption processes have been described by exponential functions, both characterised by a single time constant

Formation and characterisation of a self-assembled phthalocyanine monolayer suitable for gas sensing

Abstract The formation and characterisation of a novel self-assembled monolayer film for gas sensing are reported. The phthalocyanine 1,1′4,4′,8,8′,11,11′,15,15′,18,18′,22,22′-tetradecakishexyl-225,25′-(3,3′-dithiodipropyl)diphthalocyanine, has been synthesised from its hydroxypropyl precursor, via a two-step reaction. The disulfide functionality of the molecule has been used to produce a self-assembled phthalocyanine monolayer on a gold substrate. The phthalocyanine monolayer has been characterised using reflection absorption infrared spectroscopy (RAIRS).

Substituted phthalocyanine gas sensors

Abstract Gas sensors are playing an increasingly important role in the monitoring of workplace environments. Sublimed films of metal phthalocyanines have been successfully used as NO2 sensors, but do suffer certain limitations. Langmuir—Blodgett films of many substituted phthalocyanines have proved difficult to prepare reproducibly. An asymmetrically substituted phthalocyanine, 1,4-bis(4-hydroxybutyl) 8,11,15,18,22,25-hexaoctylphthalocyanine, designed specifically to form good-quality Langmuir—Blodgett films, has been successfully deposited. Prepared devices show a useful room-temperature response to NO2. The reproducibility, lifetime, shelflife, specificity and effects of water vapour on these devices have been investigated.

Further optical studies on Langmuir-Blodgett films of octa-substituted metal-free phthalocyanines

Abstract Ellipsometry and optical spectroscopy in the ultraviolet-visible (UV-vis.) and infra-red ranges were used to study the correlation between structure and optical properties of Langmuir-Blodgett (LB) films of octa-substituted metal-free phthalocyanines containing different alkyl chains. The thickness and refractive index of LB films and the orientation of phthalocyanine moieties in the monolayer were obtained from ellipsometric measurements and then data were compared with those from Π A isotherms of the floating layer. UV-vis. absorption spectra of LB films of the molecules show Davydov splitting of the Q band. Small changes in alkyl length lead to significant changes in the Q-band shape. The optical characteristics of monolayers are found to be different from those of multilayer films.

An interpretation of the structure of Langmuir-Blodgett films of octa-substituted metal-free phthalocyanine molecules from optical spectra

Abstract Ultraviolet-visible absorption spectra of Langmuir-Blodgett (LB) films of octa-substituted metal-free phthalocyanine molecules are decomposed into Gaussian-Lorentzian components in order to compare the in-plane molecular arrangements of the two groups of the compounds with short and long alkyl chains. LB films of long-chain molecules represent the Davydov splitting of the Q band, which corresponds to the ‘herringbone’ molecular structure and the angle between the molecules is estimated to be 75°. For short-chain molecules, the largely broadened ‘blue’ component of the Davydov doublets is suppressed and this can be explained by the domination of an anisotropic stack-like molecular arrangement in LB films.

Nanocomposite spun films based upon lead phthalocyanine

Composite phthalocyanine thin films were produced for the first time by exposure of thin films of an organic solvent soluble lead phthalocyanine derivative to H/sub 2/S gas. UV-visible absorption and photoluminescence spectral measurements indicate the probable formation of lead sulfide clusters, while the film structure and morphology were studied with atomic force microscopy.