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Semiconducting polymers based on tetraizoindole
Journal of Materials Processing Technology 119 (2001) 344±347
Semiconducting polymers based on tetraizoindole C. Boscorneaa,*, St. Tomasa, L.G. Hinescub, C. Tarabasanu-Mihailaa a
Department of Organic Technology, Polytehnica University, Bucharest, Romania b Institute for Microtechnology, Bucharest, Romania
Abstract The growing interest in the production of electronic devices are able to detect very small amounts of cellular second-messengers as NO or for monitoring gases as NO2, O2, CO2, Cl2 or other toxic gases. The metal-complex tetraizoindoles (metal phthalocyanines, MePcs) were previously shown as potential sensor materials for nitrogen oxide-sensing devices. The synthesis of nickel phthalocyanines (NiPcs), copper polyphthalocyanines (CuPcs) and aliphatic amines-condensed CuPc derivatives are described. Three new aliphatic amine-condensed CuPc derivatives as n-type organic semiconductors were obtained using an original technique conventionally used for aromatic derivatives synthesis. NiPc and aliphatic amine-substituted CuPc derivatives were deposited onto glass substrates by a high-vacuum thermal evaporation technique. Microscopic studies (interference) show that thin ®lms of vapor-deposited MePcs had a thickness of 89±220 nm. The optical properties of MePc thin ®lms have been examined by UV±Vis and IR spectrometry and the effect of NOx upon optical properties is in course. The sensor could be prepared by deposition of MePc thin ®lms on a substrate with IPID (in-plane interdigitated) electrodes for the detection of NO2. The ®nal goal of this paper was to extend both the knowledge on the synthesis of organic metal-complex tetraizoindoles and their potential use as semiconductors in NOx sensing devices. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Polyphthalocyanines; Gas sensors
1. Introduction The interaction between complex aromatic dyes and different substrates is largely gone beyond traditional applications as textile printing and hystological dying. They have reached now the hitech domain: sub-micrometric lithography; laser recordings and therapies; molecular-level structured layers; optical memories [1]; photocatalyzers; chemical sensors; biosensors. The main advantages that organic dyes take over inorganic ones are: 1. the magnitude of their nonlinear properties (about 10 times larger than inorganic compounds); 2. the easy fabrication; 3. the diversity of structure, view sensitivities, making them able to satisfy a number of optical and electrical requirements. Metal-phthalocyanines do represent such a class of organic compounds, highly useful for the fabrication of integrated circuits. The main reason lays in their intrinsic structural characteristics, their remarkable chemical and thermal stability. *
Corresponding author.
The most different phthalocyanine have the most different biomedical applications: Photosensitivity: photodynamic cancer therapy (PDT) ZnPc's sensitivity to photo-oxidation process [2]. AlPcs derivatives: subcellular photodynamic targets Ð subcellular localization pattern of dye in LOX cells [3]. SiPc: red absorption and ligands function semblants to blood LDL Ð potential to be accumulated by tumor cells [4]. MePcs (Me: Al, Eu, Nd): tumor marking agents in experimental sets for laser-induced fluorescence diagnosis [3]. Plastic surgery and immunology Pcs included in blue/latex polymer particle Ð detection of very low levels of Ag and Ab in blood serum, urine. AlPcs: sensitize human erythrocytes Ð endpoint to study chemical modification on PDT [5±8]. Antimicrobial Method for inhibiting infection or replication of HIV [9]. AlPcs: in vivo eliminating plaque bacteria from a carious lesion prior to its restoration [9,10]. CoPc: in-modified carbon epoxy electrodes for determination of organophosphate acid carbonate pesticides [11,12].
0924-0136/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 0 1 3 6 ( 0 1 ) 0 0 9 2 2 - 0
C. Boscornea et al. / Journal of Materials Processing Technology 119 (2001) 344±347
Sensors and biosensors A variety of different thin-film structure has been proposed to detect sensitively O2, NO2, O3, NH3, NOx, in the gas phase [13,17±19]. Phthalocyanine is a large planar molecule with a delocalized electron system which can easily be ionized. A phthalocyanine molecule is a good electron donor. The ring of Natoms around the central metal atoms forms a potential-well which is responsible for the semiconducting properties. MePcs were found to be very stable even in very aggressive environments. Transfer of charge between molecules in films or single crystals is only possible by crossing the potential wells. Mesubstituted phthalocyanine are proved to be p-type organic semiconductors, the majority of carriers in cleaned CuPc are p-type carriers [15]. Phthalocyanines exhibit changes of conductance in presence of very small (ppb) concentration of oxidizing/reducing gases; their bulk conductance ranges from 10 6 to 102 ohm 1 cm 1 [1,16]. The polymeric layers are gaining a better electrical conductivity, do not become exhausted in use, as ionic conductors do, and yet are more ¯exible and of lighter coloring than traditional conductive mixtures of carbon with conventional polymers. They are remarkably stable compound which sublimate far over 2008C (mostly >5008C) under vacuum [14,15]; they are attacked only by strong, concentrated acids (and reversibly by excessive moisture).
345
2. Experimental The authors succeeded in synthesizing several phthalocyanines, in order to test and use their electrical and optical properties. The chemical species obtained are metal-substituted derivatives (Cu, Ni, Co, Pb), aminated metal-derivatives and polyCuPc. The usual synthetic routes were applied to obtain the MePcs. A mixture of 1,2-dichlorobenzene, anh. CuCl2, phthalic anhydride and urea was heated and stirred at 1908C for 4 h. After cooling, the blue mixture was diluted with EtOH (5 ml) and the crude product precipitated. This was ®ltered-off and washed with hot EtOH to remove unreacted organic materials. The precipitate was then heated at 808C with DMF and DMSO and ®ltered-off. The blue precipitate was washed with hot EtOH and dried in vacuo. (CuPc)n was obtained by conversion of monobromobenzene to 1,2,4,5-tetrabromobenzene as seen in Fig. 1, and by heating a mixture of pyromellitic dianhydride, copper (2) sulfate (1:1), urea and (NH4)4Mo7O244H2O. As a test vehicle for the NOx sensor, we chose the MOS capacitor, as being the simplest electronic device able to assume detection. Two CMOS devices have been realized: a gate-accessible MOS capacitor, which failed; a gate-accessible MNOS capacitor, both of them based on the same type of substrate and undergoing the same basic processes. The method used for Pc deposition was the EDL (evaporated dyes layers technique), as evaporated Pcs at
Fig. 1. Cu polyphthalocyanine synthesis steps.
346
C. Boscornea et al. / Journal of Materials Processing Technology 119 (2001) 344±347
Fig. 2. Structure of aliphatic amines-condensed MePc derivatives and NiPc.
200±4008C under high vacuum (10 5 Torr) forms a ®lm of 60±90 nm onto glass; both thickness and speed (10 4±1 nm/ s) of deposition were controlled with a quartz balance. For polymeric Pc, much higher temperatures are required (>1200 K, with a step rate of 200 K/min). The layer to be obtained is 30 thicker (300 nm) (Fig. 2). The extended conjugation obtained by polymerization increases the conductivity by a factor of 1012±5 10 2 ohm 1 cm 1 in (CuPc)n (Fig. 3). Mask geometry was designed to offer a permanent reference measurement: a circular capacitor and a crown-shaped capacitor. The metallic substrate was alumina; each sensing site had a Pt heating element. Subsequently, an improvement of the standard MOS technology is used to obtain an Al/Si3N4/SiO2/Si-containing MNOS (see Table 1). Thin ®lm deposition is achieved at 6438C and a Si3N4 layer thickness of 580±600 nm was
Table 1 Test vehicle for gas detection MOS capacitor
MNOS capacitor
Gate accessible
Gate accessible
Monocrystalline Si wafers, n-type (1 0 0), 3±5 W cm, chemical cleaning, preceding ultraclean oxidation Ultraclean oxidation
Treatment of ultraclean oxide Chemical cleaning Ultraclean oxidation xox 45 5 nm Chemical cleaning for Al deposition
Metal configuration Chemical cleaning for postmetal thermal treatment Postmetal thermal treatment Pc deposition Electrochemical characterization
Nitride deposition Thermal deposition 6438C 10 min input 30 min annealing 20 min output Chemical cleaning Ultraclean oxidation xox 45 5 nm Chemical cleaning for Si3N4 deposition Predeposition treatment of Si3N4 Si3N4 deposition (LPCVD, 7308C, 60 10 nm) Metal configuration Chemical cleaning for postmetal thermal treatment Postmetal thermal treatment Pc deposition Pc thermal treatment Electrochemical characterization
rigorously determined. The Si2 curve has been drawn using the standard LPCVD processes. 3. Results and discussion
Fig. 3. Cu polyphthalocyanine.
The MOS capacitor was characterized by drawing the CV curves after depolarization at 5 V and sample heating for 3 min at 2508C. In the Al/Si3N4/SiO2/Si-MOS, following CuPc deposition on the gate, a threshold shift of about
C. Boscornea et al. / Journal of Materials Processing Technology 119 (2001) 344±347
347
4. Conclusions A better response to NOx presence, with MNOS capacitors (limitation of the signal level: 20±40 mV Ð needing to be severely amplified) has been obtained. Threshold voltage (VT) and flat band voltage (VFB) were used to point out the presence of the gas. Time for a sensitive detection falls in a reasonable range: 18±35 min (from no detection to saturation), but must be improved. References Fig. 4. Dynamics of threshold voltage in an MNOS capacitor.
0.1±0.3 V was recorded. A better response to NOx presence was obtained with a gate-accessible MNOS capacitor, based on the same type of substrate and undergoing the same basic processes. Threshold voltage (VT) and ¯at band voltage (VFB) were used to point out the presence of the gas. Changes of VT and VFB show that: 1. MNOS capacitors are fully able to detect small concentrations of NOx (limitation of the signal level: 20±40 nV); 2. the time for a sensitive detection falls in a reasonable range; 3. the signal level too limiting, needing to be amplified. For these two capacitors, we have determined the threshold voltage (VT) value as given in Fig. 4; then ®eld± temperature stresses have been applied (10 min; 2008C; 500 kV/cm) in order to determine the ¯at band voltage (VFB) (see Fig. 5). Changes of these two quantities testify the ability to detect the presence of gas.
Fig. 5. Dynamics of flat bands voltage in an MNOS capacitor.
[1] Q. Chen, D. Gu, J. Shu, X. Tang, F. Gan, Optical recording properties of phthalocyanine copper as a write-once read many recording medium, Proc. SPIE Int. Soc. Opt. Eng. (Adv. Photon.) 2144 (1994) 98±105. [2] V.G. Love, Liposome-mediated delivery of photosensitizers, Photochem. Photobiol. 63 (1996) 661±665. [3] Q. Peng, Subcellular photodynamic action sites of sulfonated aluminium Pcs in a human melanoma cell line, Proc. SPIE Int. Soc. Opt. Eng. 2628 (1996) 102±113. [4] B. Rihter, Three new phthalocyanines with potential for PDT studies, Proc. SPIE Int. Soc. Opt. Eng. 1645 (1992) 251±258. [5] L. Tomilova, et al., Synthesis of new sulfonated mono- and diphthalocyanines d- and f- elements and perspectives of their application in plastic surgery, Proc. SPIE Int. Soc. Opt. Eng. 2623 (1996) 62±65. [6] T. Malinski, S. Patton, B. Pierchala, Frontiers of reactive oxygen species in biology and medicine, Int. Congr. Ser. Ð Excerpta Med. 1058 (1994) 207±210. [7] A.P. Juarranz, Effect of CoPc derivatives on SCE in Brd Usubstituted chromosomes of Allium cepa, J. Plant Physiol. 132 (5) (1988) 557±560. [8] R. Tomoda, Use of CuPc membrane electrode for rapid preliminary detection of polycyclic mutagens, Mutat. Res. 164 (4) (1996) 203±208. [9] D.W. Dixon, Porphyrin and phthalocyanine antiviral compositions, J. Appl. Bacteriol. 60 (5) (1994) 550±554. [10] A.P.F. Turner, Electrochemical sensors for continuous monitoring during surgery and intensive care, Acta Anaesthesiol. Scand. 39 (104) (1995) 15±19. [11] P. Skladal, Sensitive detection of pesticides using amperometri sensors based on CoPc-modified composite electrodes and immobilized cholinesterases, Biosens. Bioelectron. 7 (5) (1992) 335±343. [12] W. Freyer, M. Hild, H. Stiel, D. Leupold, The cycloreversion of a substituted palladium phthalocyanine containing epidioxybridges, J. Inform. Rec. 24 (1998) 95±100. [13] W. Gopel, K.D. Schierbaum, D. Schmeisser, H.D. Wiemhofer, Prototype chemical sensors for the selective detection of O2 and NO2 in gases, Sens. Actuat. 17 (1989) 377±384. [14] U. Schutze, U. Weber, D. Kohl, A new microstructured silicon substrate for ultrathin gas-sensitive films, Sens. Actuat. 37±38 (1993) 751±755. [15] P. Kaul, A self-monitoring ozone gas sensor based on a microstructured device, MST News 16 (8) (1997) 89±93. [16] E.P. Goodings, Conductivity and superconductivity in polymers, Chem. Soc. Rev. 5 (1976) 114. [17] A. Rudiono, O. Shuichi, T. Manabu, Effects of photovoltaic performance of Pc thin film solar cells, Thin Solid Films 334 (1998) 187±191. [18] L. Siulelo, L. Vilakazi, N. Tebello, Interaction of nitric oxide with CoPc: kinetics, equilibria and electrocatalytic studies, Polyhedron 17 (25±26) (1998) 4415±4423. [19] F. Wolfgang, A multiphotochromic tetraanthraporphyrazine based on the involvement of molecular singlet oxygen, J. Photochem. Photobiol. A 105 (1997) 153±158.
Semiconducting polymers based on tetraizoindole C. Boscorneaa,*, St. Tomasa, L.G. Hinescub, C. Tarabasanu-Mihailaa a
Department of Organic Technology, Polytehnica University, Bucharest, Romania b Institute for Microtechnology, Bucharest, Romania
Abstract The growing interest in the production of electronic devices are able to detect very small amounts of cellular second-messengers as NO or for monitoring gases as NO2, O2, CO2, Cl2 or other toxic gases. The metal-complex tetraizoindoles (metal phthalocyanines, MePcs) were previously shown as potential sensor materials for nitrogen oxide-sensing devices. The synthesis of nickel phthalocyanines (NiPcs), copper polyphthalocyanines (CuPcs) and aliphatic amines-condensed CuPc derivatives are described. Three new aliphatic amine-condensed CuPc derivatives as n-type organic semiconductors were obtained using an original technique conventionally used for aromatic derivatives synthesis. NiPc and aliphatic amine-substituted CuPc derivatives were deposited onto glass substrates by a high-vacuum thermal evaporation technique. Microscopic studies (interference) show that thin ®lms of vapor-deposited MePcs had a thickness of 89±220 nm. The optical properties of MePc thin ®lms have been examined by UV±Vis and IR spectrometry and the effect of NOx upon optical properties is in course. The sensor could be prepared by deposition of MePc thin ®lms on a substrate with IPID (in-plane interdigitated) electrodes for the detection of NO2. The ®nal goal of this paper was to extend both the knowledge on the synthesis of organic metal-complex tetraizoindoles and their potential use as semiconductors in NOx sensing devices. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Polyphthalocyanines; Gas sensors
1. Introduction The interaction between complex aromatic dyes and different substrates is largely gone beyond traditional applications as textile printing and hystological dying. They have reached now the hitech domain: sub-micrometric lithography; laser recordings and therapies; molecular-level structured layers; optical memories [1]; photocatalyzers; chemical sensors; biosensors. The main advantages that organic dyes take over inorganic ones are: 1. the magnitude of their nonlinear properties (about 10 times larger than inorganic compounds); 2. the easy fabrication; 3. the diversity of structure, view sensitivities, making them able to satisfy a number of optical and electrical requirements. Metal-phthalocyanines do represent such a class of organic compounds, highly useful for the fabrication of integrated circuits. The main reason lays in their intrinsic structural characteristics, their remarkable chemical and thermal stability. *
Corresponding author.
The most different phthalocyanine have the most different biomedical applications: Photosensitivity: photodynamic cancer therapy (PDT) ZnPc's sensitivity to photo-oxidation process [2]. AlPcs derivatives: subcellular photodynamic targets Ð subcellular localization pattern of dye in LOX cells [3]. SiPc: red absorption and ligands function semblants to blood LDL Ð potential to be accumulated by tumor cells [4]. MePcs (Me: Al, Eu, Nd): tumor marking agents in experimental sets for laser-induced fluorescence diagnosis [3]. Plastic surgery and immunology Pcs included in blue/latex polymer particle Ð detection of very low levels of Ag and Ab in blood serum, urine. AlPcs: sensitize human erythrocytes Ð endpoint to study chemical modification on PDT [5±8]. Antimicrobial Method for inhibiting infection or replication of HIV [9]. AlPcs: in vivo eliminating plaque bacteria from a carious lesion prior to its restoration [9,10]. CoPc: in-modified carbon epoxy electrodes for determination of organophosphate acid carbonate pesticides [11,12].
0924-0136/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 4 - 0 1 3 6 ( 0 1 ) 0 0 9 2 2 - 0
C. Boscornea et al. / Journal of Materials Processing Technology 119 (2001) 344±347
Sensors and biosensors A variety of different thin-film structure has been proposed to detect sensitively O2, NO2, O3, NH3, NOx, in the gas phase [13,17±19]. Phthalocyanine is a large planar molecule with a delocalized electron system which can easily be ionized. A phthalocyanine molecule is a good electron donor. The ring of Natoms around the central metal atoms forms a potential-well which is responsible for the semiconducting properties. MePcs were found to be very stable even in very aggressive environments. Transfer of charge between molecules in films or single crystals is only possible by crossing the potential wells. Mesubstituted phthalocyanine are proved to be p-type organic semiconductors, the majority of carriers in cleaned CuPc are p-type carriers [15]. Phthalocyanines exhibit changes of conductance in presence of very small (ppb) concentration of oxidizing/reducing gases; their bulk conductance ranges from 10 6 to 102 ohm 1 cm 1 [1,16]. The polymeric layers are gaining a better electrical conductivity, do not become exhausted in use, as ionic conductors do, and yet are more ¯exible and of lighter coloring than traditional conductive mixtures of carbon with conventional polymers. They are remarkably stable compound which sublimate far over 2008C (mostly >5008C) under vacuum [14,15]; they are attacked only by strong, concentrated acids (and reversibly by excessive moisture).
345
2. Experimental The authors succeeded in synthesizing several phthalocyanines, in order to test and use their electrical and optical properties. The chemical species obtained are metal-substituted derivatives (Cu, Ni, Co, Pb), aminated metal-derivatives and polyCuPc. The usual synthetic routes were applied to obtain the MePcs. A mixture of 1,2-dichlorobenzene, anh. CuCl2, phthalic anhydride and urea was heated and stirred at 1908C for 4 h. After cooling, the blue mixture was diluted with EtOH (5 ml) and the crude product precipitated. This was ®ltered-off and washed with hot EtOH to remove unreacted organic materials. The precipitate was then heated at 808C with DMF and DMSO and ®ltered-off. The blue precipitate was washed with hot EtOH and dried in vacuo. (CuPc)n was obtained by conversion of monobromobenzene to 1,2,4,5-tetrabromobenzene as seen in Fig. 1, and by heating a mixture of pyromellitic dianhydride, copper (2) sulfate (1:1), urea and (NH4)4Mo7O244H2O. As a test vehicle for the NOx sensor, we chose the MOS capacitor, as being the simplest electronic device able to assume detection. Two CMOS devices have been realized: a gate-accessible MOS capacitor, which failed; a gate-accessible MNOS capacitor, both of them based on the same type of substrate and undergoing the same basic processes. The method used for Pc deposition was the EDL (evaporated dyes layers technique), as evaporated Pcs at
Fig. 1. Cu polyphthalocyanine synthesis steps.
346
C. Boscornea et al. / Journal of Materials Processing Technology 119 (2001) 344±347
Fig. 2. Structure of aliphatic amines-condensed MePc derivatives and NiPc.
200±4008C under high vacuum (10 5 Torr) forms a ®lm of 60±90 nm onto glass; both thickness and speed (10 4±1 nm/ s) of deposition were controlled with a quartz balance. For polymeric Pc, much higher temperatures are required (>1200 K, with a step rate of 200 K/min). The layer to be obtained is 30 thicker (300 nm) (Fig. 2). The extended conjugation obtained by polymerization increases the conductivity by a factor of 1012±5 10 2 ohm 1 cm 1 in (CuPc)n (Fig. 3). Mask geometry was designed to offer a permanent reference measurement: a circular capacitor and a crown-shaped capacitor. The metallic substrate was alumina; each sensing site had a Pt heating element. Subsequently, an improvement of the standard MOS technology is used to obtain an Al/Si3N4/SiO2/Si-containing MNOS (see Table 1). Thin ®lm deposition is achieved at 6438C and a Si3N4 layer thickness of 580±600 nm was
Table 1 Test vehicle for gas detection MOS capacitor
MNOS capacitor
Gate accessible
Gate accessible
Monocrystalline Si wafers, n-type (1 0 0), 3±5 W cm, chemical cleaning, preceding ultraclean oxidation Ultraclean oxidation
Treatment of ultraclean oxide Chemical cleaning Ultraclean oxidation xox 45 5 nm Chemical cleaning for Al deposition
Metal configuration Chemical cleaning for postmetal thermal treatment Postmetal thermal treatment Pc deposition Electrochemical characterization
Nitride deposition Thermal deposition 6438C 10 min input 30 min annealing 20 min output Chemical cleaning Ultraclean oxidation xox 45 5 nm Chemical cleaning for Si3N4 deposition Predeposition treatment of Si3N4 Si3N4 deposition (LPCVD, 7308C, 60 10 nm) Metal configuration Chemical cleaning for postmetal thermal treatment Postmetal thermal treatment Pc deposition Pc thermal treatment Electrochemical characterization
rigorously determined. The Si2 curve has been drawn using the standard LPCVD processes. 3. Results and discussion
Fig. 3. Cu polyphthalocyanine.
The MOS capacitor was characterized by drawing the CV curves after depolarization at 5 V and sample heating for 3 min at 2508C. In the Al/Si3N4/SiO2/Si-MOS, following CuPc deposition on the gate, a threshold shift of about
C. Boscornea et al. / Journal of Materials Processing Technology 119 (2001) 344±347
347
4. Conclusions A better response to NOx presence, with MNOS capacitors (limitation of the signal level: 20±40 mV Ð needing to be severely amplified) has been obtained. Threshold voltage (VT) and flat band voltage (VFB) were used to point out the presence of the gas. Time for a sensitive detection falls in a reasonable range: 18±35 min (from no detection to saturation), but must be improved. References Fig. 4. Dynamics of threshold voltage in an MNOS capacitor.
0.1±0.3 V was recorded. A better response to NOx presence was obtained with a gate-accessible MNOS capacitor, based on the same type of substrate and undergoing the same basic processes. Threshold voltage (VT) and ¯at band voltage (VFB) were used to point out the presence of the gas. Changes of VT and VFB show that: 1. MNOS capacitors are fully able to detect small concentrations of NOx (limitation of the signal level: 20±40 nV); 2. the time for a sensitive detection falls in a reasonable range; 3. the signal level too limiting, needing to be amplified. For these two capacitors, we have determined the threshold voltage (VT) value as given in Fig. 4; then ®eld± temperature stresses have been applied (10 min; 2008C; 500 kV/cm) in order to determine the ¯at band voltage (VFB) (see Fig. 5). Changes of these two quantities testify the ability to detect the presence of gas.
Fig. 5. Dynamics of flat bands voltage in an MNOS capacitor.
[1] Q. Chen, D. Gu, J. Shu, X. Tang, F. Gan, Optical recording properties of phthalocyanine copper as a write-once read many recording medium, Proc. SPIE Int. Soc. Opt. Eng. (Adv. Photon.) 2144 (1994) 98±105. [2] V.G. Love, Liposome-mediated delivery of photosensitizers, Photochem. Photobiol. 63 (1996) 661±665. [3] Q. Peng, Subcellular photodynamic action sites of sulfonated aluminium Pcs in a human melanoma cell line, Proc. SPIE Int. Soc. Opt. Eng. 2628 (1996) 102±113. [4] B. Rihter, Three new phthalocyanines with potential for PDT studies, Proc. SPIE Int. Soc. Opt. Eng. 1645 (1992) 251±258. [5] L. Tomilova, et al., Synthesis of new sulfonated mono- and diphthalocyanines d- and f- elements and perspectives of their application in plastic surgery, Proc. SPIE Int. Soc. Opt. Eng. 2623 (1996) 62±65. [6] T. Malinski, S. Patton, B. Pierchala, Frontiers of reactive oxygen species in biology and medicine, Int. Congr. Ser. Ð Excerpta Med. 1058 (1994) 207±210. [7] A.P. Juarranz, Effect of CoPc derivatives on SCE in Brd Usubstituted chromosomes of Allium cepa, J. Plant Physiol. 132 (5) (1988) 557±560. [8] R. Tomoda, Use of CuPc membrane electrode for rapid preliminary detection of polycyclic mutagens, Mutat. Res. 164 (4) (1996) 203±208. [9] D.W. Dixon, Porphyrin and phthalocyanine antiviral compositions, J. Appl. Bacteriol. 60 (5) (1994) 550±554. [10] A.P.F. Turner, Electrochemical sensors for continuous monitoring during surgery and intensive care, Acta Anaesthesiol. Scand. 39 (104) (1995) 15±19. [11] P. Skladal, Sensitive detection of pesticides using amperometri sensors based on CoPc-modified composite electrodes and immobilized cholinesterases, Biosens. Bioelectron. 7 (5) (1992) 335±343. [12] W. Freyer, M. Hild, H. Stiel, D. Leupold, The cycloreversion of a substituted palladium phthalocyanine containing epidioxybridges, J. Inform. Rec. 24 (1998) 95±100. [13] W. Gopel, K.D. Schierbaum, D. Schmeisser, H.D. Wiemhofer, Prototype chemical sensors for the selective detection of O2 and NO2 in gases, Sens. Actuat. 17 (1989) 377±384. [14] U. Schutze, U. Weber, D. Kohl, A new microstructured silicon substrate for ultrathin gas-sensitive films, Sens. Actuat. 37±38 (1993) 751±755. [15] P. Kaul, A self-monitoring ozone gas sensor based on a microstructured device, MST News 16 (8) (1997) 89±93. [16] E.P. Goodings, Conductivity and superconductivity in polymers, Chem. Soc. Rev. 5 (1976) 114. [17] A. Rudiono, O. Shuichi, T. Manabu, Effects of photovoltaic performance of Pc thin film solar cells, Thin Solid Films 334 (1998) 187±191. [18] L. Siulelo, L. Vilakazi, N. Tebello, Interaction of nitric oxide with CoPc: kinetics, equilibria and electrocatalytic studies, Polyhedron 17 (25±26) (1998) 4415±4423. [19] F. Wolfgang, A multiphotochromic tetraanthraporphyrazine based on the involvement of molecular singlet oxygen, J. Photochem. Photobiol. A 105 (1997) 153±158.