Phthalocyanine thin films sensitization

B. A. (1993) Phthalocyanine aggregates on metal dichalcogenide surfeces dye sensitization on tin disulfide semiconductor electrodes by ordered and disordered diloroindium phthalocyanine thin films. J. Phys. Chem., 97, 2690 2698. 

Nonomura, K., T. Loewenstein, E. Michaelis, D. Wohrle, T. Yoshida, H. Minoura, and D. Schlettwein (2006). Photoelectrochemical characterisation and optimisation of electrodeposited ZnO thin films sensitized by porphyrins and phthalocyanines. Phys.Chem.Chem.Phys. submitted. 

Sergeyeva, T.A., et al. Hydrogen peroxide-sensitive enzyme sensor based on phthalocyanine thin film. Analytica Chimica Acta 391(3), 289-297 (1999)... 

Nonomura K, Loewenstein T, Michaelis E, Wohrle D, Oekermann T, Yoshida T, Minoura H, Schlettwein D (2006) Photoelectrochemical characterization of electrodeposited ZnO thin films sensitized by porph5oins and phthalocyanines. Phys Chem Chem Phys 8 3867-3875... 

Idowu M, Loewenstein T, Hastall A, Nyokong T, Schlettwein D (2010) Photoelectrochemical characterization of electrodeposited ZnO thin films sensitized by octacarboxymetallophthalocyanine derivatives. J Porph Phthalocyanin 14 142-149 Masilela N, Nombona N, Loewenstein T, Nyokong T, Sehlettwein D (2010) S5nnmetrically and unsymmetrically substituted carboxy phthalocyanines as sensitizers for nanoporous ZnO films. J Porph Phthalocyanin 14 985-992... 

Phthalocyanines have been used to incorporate semiconductor properties in polymers (182) or to develop a thin-film transistor (183). Phthalocyanines and their derivatives can act as dyes in color photography (qv) (184) or electrophotography (185). Light-sensitive compositions for use on Hthographic plates are comprised in part of copper phthalocyanine blue (186). Dichlorosilicon phthalocyanine [19333-10-9] has been used in the... 

The results illustrated above show that the CFT method is suitable for making chemical-sensor measurements using both bulk polymers and, in particular, thin film materials that are intrinsically weak conductors. Therefore, the CFT looks premising for such materials as poly(phenylacetylene) derivatives 24., for which carefully shielded electrometer measurements have been required in the past because of current levels at the threshold of detectability. Furthermore, the fact that the CFT always makes AC measurements reduces the problem of DC polarization of electrodes. In addition, the CFT approach should be suitable for other "chemiresistor" applications, such as the metal-substituted phthalocyanines proposed by Jarvis et. al. 2 and for Langmuir—Blodgett films 26. which, because they are so thin, may prove impossible to use in parallel-plate form, but which can be routinely used with the high-sensitivity interdigi-tated-electrode approach provided by the CFT. 

Our attention has been directed to modifying Sn02 electrodes and later, metal electrodes with very thin films (10-100 molecular layers) of phthalocyanines which appear to aggregate when sublimed. The oriented phthalocyanine phase or phases sensitize the response of the Sn02 electrodes with efficiencies many times greater than monomolecular layers of covalently attached chromophores or randomly oriented multilayer dye films (9). Our initial studies have been conducted with phthalocya-nines which we expected would orient in a linear "pancake-stack," by virtue of the interaction between the central metal atoms — either a covalent bond or a strong electrostatic interaction. 

Compact chemical sensors can be broadly classified as being based on electronic or optical readout mechanisms [28]. The electronic sensor types would include resistive, capacitive, surface acoustic wave (SAW), electrochemical, and mass (e.g., quartz crystal microbalance (QCM) and microelectromechanical systems (MEMSs)). Chemical specificity of most sensors relies critically on the materials designed either as part of the sensor readout itself (e.g., semiconducting metal oxides, nanoparticle films, or polymers in resistive sensors) or on a chemically sensitive coating (e.g., polymers used in MEMS, QCM, and SAW sensors). This review will focus on the mechanism of sensing in conductivity based chemical sensors that contain a semiconducting thin film of a phthalocyanine or metal phthalocyanine sensing layer. 

Sensor fabrication has been accomplished in various ways. One method [29] combines the phthalocyanine compound with stearic acid to form a bonded substance which is then dissolved in an organic solvent. The mixture is deposited by one of several possible methods onto a substrate and subsequently fired to remove the vehicle. A thin-film model, manufactured by vacuum sublimation over interdigited electrodes on 3 mm x 3 mm alumina substrates [28], exhibited sensitivity to CI2, F2, and BCI3, but not to common reducing species. The films operating continuously did not survive longer than 6 months. 

Hu, W. et al.. The gas sensitivity of a metal-insulator-semiconductor field-effect-transistor based on Langmuir-Blodgett films of a new asymmetrically substituted phthalocyanine. Thin Solid Films, 360, 256, 2000. 

Gu C., Sun L., Zhang T., Li T., and Zhang X., High-sensitivity phthalocyanine LB film gas sensor based on field effect transistors. Thin Solid Films, 327-329, 383-386, 1998. 

Although there is no tt-tt interaction between phthalocyanines/porphyrins and alcohols, there are many works carried out in sensing alcohols by using thin films of phthalocyanines and porphyrins. LB films of tetra-a-(2,2,4-trimethyl-3-pentyloxy) CuPc show good sensitivity to vapor of alcohol [61]. The response time of the LB film to alcohol is 2 minutes and recovery time is 1 minute. The response should be due to the hydrogen bonding between alcohol and the substituents. 

In summary, the position of the frontier electron energy levels (HOMO and LUMO) of porphyrins and phthalocyanines can be finely tuned by the appropriate combination of central metal and substituted ligand as detected in photoelectron spectroscopy or in the redox potentials. A rich redox chemistry in interplay with a number of reactants and counterions has been estabhshed. A systematic consideration of the electrochemical and photoelectrochemical characteristics of porphyrins and phthalocyanines as individual molecules in solution, as molecules adsorbed at surfaces, and as molecular thin films serving to mimic the characteristics of molecular aggregates is of much relevance to the choosing or designing of optimized porphyrin or phthalocyanine sensitizers for DSSCs. 

The photoelectrochemlcal properties of PcIn(Cl) thin films were also investigated on single-crystalhne layered semiconductor electrodes of SnS2 or MoS2 These surfaces turned out to provide a suitable substrate to deposit highly ordered epitaxial phthalocyanine films by OMBE and to also ahow the study of such films as sensitizers for the n-type semiconductors. Very narrow absorption spectra and also photocurrent action spectra could be obtained speaking... 

Kaneko, M., D. Wohrle, D. Schlettwein, and V. Schmidt (1988). Dioxygen sensitivity of a photoexcited thin film of phthalocyanine dispersed in poly(vinylcarbazole). Makromol. Chem. 189, 2419-2425. 

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