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Influence of gamma radiation on neodymium bisphthalocyanine
Optical Materials 26 (2004) 163–166 www.elsevier.com/locate/optmat
Influence of gamma radiation on neodymium bisphthalocyanine A. Łukowiak a
a,*
, E. Łukowiak b, M. Jasiorski a, K. Maruszewski
a,b
, W. Streßk
b
Institute of Material Sciences and Applied Mechanics, Technical University of Wrocław, Smoluchowskiego 25, 50-370 Wrocław, Poland b Institute for Low Temperature and Structures Research, Polish Academic of Science, Okolna 2, 50-950 Wrocław, Poland Available online 13 December 2003
Abstract The neodymium(III) bisphthalocyanine (NdPc2 ) discoloration under gamma radiation has been studied. The NdPc2 entrapped in silica matrices have been prepared by the sol–gel method. The decomposition of the dye under gamma rays leads to decay of the absorption bands in the Q-band region. The differences in behavior of NdPc2 in liquid solutions and in the silica matrices are discussed. The sol–gel matrix seems to stabilize the entrapped molecule. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Sol–gel; Neodymium(III) bisphthalocyanine; Gamma radiation
1. Introduction
2. Experimental
Metallophthalocyanines (MPcs) are a broad class of compounds which can be used as dyes, paints, liquid crystals, chemical sensors, laser dyes, optical limiters or photosensitizers for photodynamic therapy [1–5]. The complexes are colored due to their intense absorption band in the visible region between 600 and 700 nm (called the Q-band) [6]. The sol–gel method can be used to obtain inorganic matrices doped with organic compounds. Silica matrix shows very good transmission properties in the visible region. MPcs can be incorporated during the sol stage at room temperature. The disadvantage is that these compounds are almost insoluble in most solvents. They also show tendency to dimerization and aggregation [7,8]. Arshak et al. have described the possibility of using thick films of manganese phthalocyanine in gamma radiation dosimetry [9]. There exist also other reports concerning dosimeters in which dyes in solutions or in solid matrices change their optical properties under gamma irradiation [10,11]. This work considers synthesis of NdPc2 -dopped (Fig. 1) sol–gel materials and influence of gamma irradiation on the absorption spectrum of the dye in the dimethyloformamide (DMF) solution, DMF:H2 O (2:1) solution and in the sol–gel matrix.
The silica samples were prepared using the sol–gel method. Tetraethoxysilane (TEOS; Alfa Aesar) was mixed with distilled water and with HClðaqÞ as a catalyst. The reagents mole ratio (TEOS:H2 O:HCl) was 1:16:0.01. The solution was stirred at room temperature for 90 min. Then NdPc2 dissolved in DMF (POCh Gliwice) was added to yield 11.4 lM dye concentration in the sol. The mixture was stirred for 30 min and the homogeneous sol was put into a container. To obtain a gel the pH of the solution was set at about 8 by adding 0.66 M NH3ðaqÞ . After gelation and drying at room temperature, transparent monolithic pieces were obtained (diameter: 15 mm). The silica bulks not doped with the dye and possessing the same dimensions were also prepared as a reference. The xerogels doped with NdPc2 were green, transparent and monolithic. Due to the condition of gelation and drying (room temperature, closed containers opened by stages) the bulks were without cracks. The concentration of NdPc2 in the solutions (DMF and DMF:H2 O, 2:1) was 42.7 lM. It is difficult to determine the final concentration in the silica matrix because of the samples shrinkage. The samples were exposed to 60 Co radiation source at a dose rate of 15.8 Gy/min. The irradiation process was carried out at room temperature and the samples were stored in the dark. The absorption spectra were recorded using a Varian Cary 2300 spectrophotometer.
*
Corresponding author. Fax: +48-71-3211235. E-mail address: [email protected] (A. Łukowiak).
0925-3467/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2003.11.016
164
A. Łukowiak et al. / Optical Materials 26 (2004) 163–166
Fig. 1. The molecular structure of neodymium(III) bisphthalocyanine (NdPc2 ).
3. Results and discussion The absorption spectra of NdPc2 in the solutions are presented in Fig. 2. The complex in DMF and in DMF:H2 O has two bands in the visible region (632 and 670; 635 and 673, respectively). The longer-wavelength band forms a shoulder. These two bands can be assigned to the monomeric (670 nm) and dimeric (630 nm) forms of the phthalocyanine [12]. The concentration of the dye is quite high, thus the second form dominates in the solutions. The addition of water causes slight red shift of the bands. It has also influenced the decay of the Q-bands under gamma irradiation. The absorption intensity decrease is slower when water is present in the solution (Fig. 2). For NdPc2 in DMF at the beginning of irradiation the longer-wavelength band increases and the shorter-wavelength decreases its intensity. For the doses of more than about 0.4 kGy the decrease of the absorption intensity is noticeable for both bands. The monomer/dimer absorption ratio still increases up to about 1 kGy. This effect can be caused by faster degradation of the dimer form. The other possible reason is
Fig. 2. Absorption spectra of NdPc2 in (a) DMF, (b) DMF:H2 O (2:1) before and after gamma irradiation.
that the monomer¡dimer equilibrium in the solution shifts under gamma rays. In DMF:H2 O solution the monomer/dimer absorption intensity ratio is constant up to 3.5 kGy. The decrease in the dimer form seems to appear in the later stage of irradiation. In both cases the initial green color almost disappears at doses of about 10 kGy. The absorption spectra of NdPc2 in silica matrix are different (Fig. 3). There is one broad band with maximum at 665 nm (and a shoulder at about 590 nm). When a dose of gamma radiation approaches 20 kGy the blue shift is observed (653 nm) and an increase of the Q-band intensity. Also, the shoulder disappears. Further irradiation causes decrease of the band intensity. The shape of the band (a broad feature with asymmetric shoulders after irradiation) and the shift indicates that two bands might overlap. Like in solutions, the longer-wavelength band can be assigned to the monomeric and the other to the aggregated forms of the phthalocyanine [12–14]. It is possible that faster degradation of the monomer form (contrary to the effect in the solutions) causes apparent shift and the absorption increase. The change in the monomer¡dimer equilibrium is also possible. In the later stage of irradiation, when new equilibrium is set, no shift is observed and the absorption of both forms decrease. The decay of absorption intensity in xerogel is much slower as compared to the solutions. The same effect was observed for carotene and chlorophyll in solution and silica matrices [11]. Even up to 1100 kGy the doped bulk sample is still green and the sol–gel matrix has very good transmission properties in the investigated region (500– 800 nm). Further investigations for higher radiation doses were difficult because the bulks both with and without the dye started to disintegrate. Fig. 4 shows changes in the absorbance of the dye in the solutions at 632 nm versus the dose of gamma
Fig. 3. Absorption spectra of NdPc2 in sol–gel matrix before and after gamma irradiation.
A. Łukowiak et al. / Optical Materials 26 (2004) 163–166
165
decomposition rate in the sol–gel matrix might be related to lower concentration of free radicals formed in it upon the gamma irradiation. Another possibility is the matrix-induced change of the macrocycle complex surroundings, which might increase the dye stability. The observed initial increase of the absorption could be caused by the matrix structure changes occurring at low gamma radiation levels, leading to the increase of the entrapped dye extinction coefficient and to the changes in the absorption band.
4. Conclusions
Fig. 4. Absorption intensity changes in solutions (at 632 nm) versus dose of gamma irradiation (fitted by Orgin).
radiation. For NdPc2 in DMF the decay is exponential but in DMF:H2 O solution it is linear. The behavior of NdPc2 entrapped in the sol–gel matrix is presented in Fig. 5 (absorption at 653 nm). In this case the most important feature, as compared to the dye liquid solutions, is much slower disappearance of the dye absorption. Further interesting fact is the observed initial increase in the phthalocyanine absorption. The complex undergoes decomposition under gamma radiation. The radicals formed under high-energy radiation can be responsible for the degradation. The macrocyclic ring is probably sensitive to radicals attack [15,16]. The cleavage of the carbon–carbon, carbon– hydrogen, carbon–nitrogen bonds is possible in the dye molecules [11]. The apparent decrease in the dye
Green, transparent and monolithic xerogels doped with NdPc2 were obtained. The optical properties of NdPc2 in solutions and silica matrix were investigated before and after exposure to gamma radiation. Gamma rays cause the complex decomposition as monitored by the complex discoloration. The degradation occurs slightly faster in DMF than in DMF:H2 O. The absorbance decrease is much slower for the xerogels doped with NdPc2 . Besides, in the solutions the monomeric form seems to be more stable at the beginning of irradiation contrary to the effect in the gel (the absorption of the dimeric form decreases more slowly). The sol–gel matrix seems to stabilize the entrapped molecules of the dye.
Acknowledgements The authors would like to thank J. Kaleci nski and T. Morawska-Kowal for their help.
References
Fig. 5. Absorption intensity changes (at 653 nm) versus dose of gamma irradiation for NdPc2 in xerogel. Insert: linear absorbance changes from 0 to 2 kGy (fitted by Orgin).
[1] C.G. Claessens, W.J. Blau, M. Cook, M. Hanack, R.J.M. Nolte, T. Torres, D. W€ ohrle, Monatsh. Chem. 132 (2001) 3. [2] H. Xia, M. Nogami, J. Mater. Sci. 34 (1999) 3053. [3] J.W. Perry, K. Manson, S.R. Marder, K.J. Perry, Opt. Lett. 19 (1994) 625. [4] B.T. Bott, A. Jones, Sens. Actuators 5 (1984) 43. [5] J.W. Perry, K. Manson, I.-Y.S. Lee, et al., Science 273 (1996) 1533. [6] A.M. Schaffer, M. Gouterman, Theor. Chim. Acta 30 (1973) 9. [7] P.D. Fuqua, B. Dunn, J.J. Zink, J. Sol–Gel Sci. Technol. 11 (1998) 241. [8] V.V. Sapunov, J. Appl. Spectrosc. 68 (2001) 727. [9] A. Arshak, S. Zleetni, K. Arshak, Sensors 2 (2002) 174. [10] A.F. Maged, M.S.A. Hamza, E.A. Saad, Radiat. Phys. Chem. 50 (1997) 179. [11] J. Ramirez-Nino, D. Mendoza, V.M. Castano, Radiat. Meas. 29 (1998) 195. [12] K. Maruszewski, L. Czernicki, W. Waclawek, W. Strek, J. Mol. Struct. 404 (1997) 141.
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[13] K. Maruszewski, W. Strek, M. Jasiorski, P. Deren, Z. Ziembik, I. Czerniak, E. Czernia, W. Waclawek, J. Mol. Struct. 519 (2000) 125. [14] R. Litr an, E. Blanco, M. Ramırez-Del-Solar, L. Esquivias, J. Sol– Gel Sci. Technol. 8 (1997) 985.
[15] G.M. Zimina, G.P. Tkhorzhnitskii, D.V. Krasnyi, A.V. Vannikov, High Energ. Chem. 36 (2002) 7. [16] E. Kalecinska, J. Kalecinski, M. Krowicka, Radiat. Phys. Chem. 60 (2001) 169.
Influence of gamma radiation on neodymium bisphthalocyanine A. Łukowiak a
a,*
, E. Łukowiak b, M. Jasiorski a, K. Maruszewski
a,b
, W. Streßk
b
Institute of Material Sciences and Applied Mechanics, Technical University of Wrocław, Smoluchowskiego 25, 50-370 Wrocław, Poland b Institute for Low Temperature and Structures Research, Polish Academic of Science, Okolna 2, 50-950 Wrocław, Poland Available online 13 December 2003
Abstract The neodymium(III) bisphthalocyanine (NdPc2 ) discoloration under gamma radiation has been studied. The NdPc2 entrapped in silica matrices have been prepared by the sol–gel method. The decomposition of the dye under gamma rays leads to decay of the absorption bands in the Q-band region. The differences in behavior of NdPc2 in liquid solutions and in the silica matrices are discussed. The sol–gel matrix seems to stabilize the entrapped molecule. Ó 2003 Elsevier B.V. All rights reserved. Keywords: Sol–gel; Neodymium(III) bisphthalocyanine; Gamma radiation
1. Introduction
2. Experimental
Metallophthalocyanines (MPcs) are a broad class of compounds which can be used as dyes, paints, liquid crystals, chemical sensors, laser dyes, optical limiters or photosensitizers for photodynamic therapy [1–5]. The complexes are colored due to their intense absorption band in the visible region between 600 and 700 nm (called the Q-band) [6]. The sol–gel method can be used to obtain inorganic matrices doped with organic compounds. Silica matrix shows very good transmission properties in the visible region. MPcs can be incorporated during the sol stage at room temperature. The disadvantage is that these compounds are almost insoluble in most solvents. They also show tendency to dimerization and aggregation [7,8]. Arshak et al. have described the possibility of using thick films of manganese phthalocyanine in gamma radiation dosimetry [9]. There exist also other reports concerning dosimeters in which dyes in solutions or in solid matrices change their optical properties under gamma irradiation [10,11]. This work considers synthesis of NdPc2 -dopped (Fig. 1) sol–gel materials and influence of gamma irradiation on the absorption spectrum of the dye in the dimethyloformamide (DMF) solution, DMF:H2 O (2:1) solution and in the sol–gel matrix.
The silica samples were prepared using the sol–gel method. Tetraethoxysilane (TEOS; Alfa Aesar) was mixed with distilled water and with HClðaqÞ as a catalyst. The reagents mole ratio (TEOS:H2 O:HCl) was 1:16:0.01. The solution was stirred at room temperature for 90 min. Then NdPc2 dissolved in DMF (POCh Gliwice) was added to yield 11.4 lM dye concentration in the sol. The mixture was stirred for 30 min and the homogeneous sol was put into a container. To obtain a gel the pH of the solution was set at about 8 by adding 0.66 M NH3ðaqÞ . After gelation and drying at room temperature, transparent monolithic pieces were obtained (diameter: 15 mm). The silica bulks not doped with the dye and possessing the same dimensions were also prepared as a reference. The xerogels doped with NdPc2 were green, transparent and monolithic. Due to the condition of gelation and drying (room temperature, closed containers opened by stages) the bulks were without cracks. The concentration of NdPc2 in the solutions (DMF and DMF:H2 O, 2:1) was 42.7 lM. It is difficult to determine the final concentration in the silica matrix because of the samples shrinkage. The samples were exposed to 60 Co radiation source at a dose rate of 15.8 Gy/min. The irradiation process was carried out at room temperature and the samples were stored in the dark. The absorption spectra were recorded using a Varian Cary 2300 spectrophotometer.
*
Corresponding author. Fax: +48-71-3211235. E-mail address: [email protected] (A. Łukowiak).
0925-3467/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.optmat.2003.11.016
164
A. Łukowiak et al. / Optical Materials 26 (2004) 163–166
Fig. 1. The molecular structure of neodymium(III) bisphthalocyanine (NdPc2 ).
3. Results and discussion The absorption spectra of NdPc2 in the solutions are presented in Fig. 2. The complex in DMF and in DMF:H2 O has two bands in the visible region (632 and 670; 635 and 673, respectively). The longer-wavelength band forms a shoulder. These two bands can be assigned to the monomeric (670 nm) and dimeric (630 nm) forms of the phthalocyanine [12]. The concentration of the dye is quite high, thus the second form dominates in the solutions. The addition of water causes slight red shift of the bands. It has also influenced the decay of the Q-bands under gamma irradiation. The absorption intensity decrease is slower when water is present in the solution (Fig. 2). For NdPc2 in DMF at the beginning of irradiation the longer-wavelength band increases and the shorter-wavelength decreases its intensity. For the doses of more than about 0.4 kGy the decrease of the absorption intensity is noticeable for both bands. The monomer/dimer absorption ratio still increases up to about 1 kGy. This effect can be caused by faster degradation of the dimer form. The other possible reason is
Fig. 2. Absorption spectra of NdPc2 in (a) DMF, (b) DMF:H2 O (2:1) before and after gamma irradiation.
that the monomer¡dimer equilibrium in the solution shifts under gamma rays. In DMF:H2 O solution the monomer/dimer absorption intensity ratio is constant up to 3.5 kGy. The decrease in the dimer form seems to appear in the later stage of irradiation. In both cases the initial green color almost disappears at doses of about 10 kGy. The absorption spectra of NdPc2 in silica matrix are different (Fig. 3). There is one broad band with maximum at 665 nm (and a shoulder at about 590 nm). When a dose of gamma radiation approaches 20 kGy the blue shift is observed (653 nm) and an increase of the Q-band intensity. Also, the shoulder disappears. Further irradiation causes decrease of the band intensity. The shape of the band (a broad feature with asymmetric shoulders after irradiation) and the shift indicates that two bands might overlap. Like in solutions, the longer-wavelength band can be assigned to the monomeric and the other to the aggregated forms of the phthalocyanine [12–14]. It is possible that faster degradation of the monomer form (contrary to the effect in the solutions) causes apparent shift and the absorption increase. The change in the monomer¡dimer equilibrium is also possible. In the later stage of irradiation, when new equilibrium is set, no shift is observed and the absorption of both forms decrease. The decay of absorption intensity in xerogel is much slower as compared to the solutions. The same effect was observed for carotene and chlorophyll in solution and silica matrices [11]. Even up to 1100 kGy the doped bulk sample is still green and the sol–gel matrix has very good transmission properties in the investigated region (500– 800 nm). Further investigations for higher radiation doses were difficult because the bulks both with and without the dye started to disintegrate. Fig. 4 shows changes in the absorbance of the dye in the solutions at 632 nm versus the dose of gamma
Fig. 3. Absorption spectra of NdPc2 in sol–gel matrix before and after gamma irradiation.
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165
decomposition rate in the sol–gel matrix might be related to lower concentration of free radicals formed in it upon the gamma irradiation. Another possibility is the matrix-induced change of the macrocycle complex surroundings, which might increase the dye stability. The observed initial increase of the absorption could be caused by the matrix structure changes occurring at low gamma radiation levels, leading to the increase of the entrapped dye extinction coefficient and to the changes in the absorption band.
4. Conclusions
Fig. 4. Absorption intensity changes in solutions (at 632 nm) versus dose of gamma irradiation (fitted by Orgin).
radiation. For NdPc2 in DMF the decay is exponential but in DMF:H2 O solution it is linear. The behavior of NdPc2 entrapped in the sol–gel matrix is presented in Fig. 5 (absorption at 653 nm). In this case the most important feature, as compared to the dye liquid solutions, is much slower disappearance of the dye absorption. Further interesting fact is the observed initial increase in the phthalocyanine absorption. The complex undergoes decomposition under gamma radiation. The radicals formed under high-energy radiation can be responsible for the degradation. The macrocyclic ring is probably sensitive to radicals attack [15,16]. The cleavage of the carbon–carbon, carbon– hydrogen, carbon–nitrogen bonds is possible in the dye molecules [11]. The apparent decrease in the dye
Green, transparent and monolithic xerogels doped with NdPc2 were obtained. The optical properties of NdPc2 in solutions and silica matrix were investigated before and after exposure to gamma radiation. Gamma rays cause the complex decomposition as monitored by the complex discoloration. The degradation occurs slightly faster in DMF than in DMF:H2 O. The absorbance decrease is much slower for the xerogels doped with NdPc2 . Besides, in the solutions the monomeric form seems to be more stable at the beginning of irradiation contrary to the effect in the gel (the absorption of the dimeric form decreases more slowly). The sol–gel matrix seems to stabilize the entrapped molecules of the dye.
Acknowledgements The authors would like to thank J. Kaleci nski and T. Morawska-Kowal for their help.
References
Fig. 5. Absorption intensity changes (at 653 nm) versus dose of gamma irradiation for NdPc2 in xerogel. Insert: linear absorbance changes from 0 to 2 kGy (fitted by Orgin).
[1] C.G. Claessens, W.J. Blau, M. Cook, M. Hanack, R.J.M. Nolte, T. Torres, D. W€ ohrle, Monatsh. Chem. 132 (2001) 3. [2] H. Xia, M. Nogami, J. Mater. Sci. 34 (1999) 3053. [3] J.W. Perry, K. Manson, S.R. Marder, K.J. Perry, Opt. Lett. 19 (1994) 625. [4] B.T. Bott, A. Jones, Sens. Actuators 5 (1984) 43. [5] J.W. Perry, K. Manson, I.-Y.S. Lee, et al., Science 273 (1996) 1533. [6] A.M. Schaffer, M. Gouterman, Theor. Chim. Acta 30 (1973) 9. [7] P.D. Fuqua, B. Dunn, J.J. Zink, J. Sol–Gel Sci. Technol. 11 (1998) 241. [8] V.V. Sapunov, J. Appl. Spectrosc. 68 (2001) 727. [9] A. Arshak, S. Zleetni, K. Arshak, Sensors 2 (2002) 174. [10] A.F. Maged, M.S.A. Hamza, E.A. Saad, Radiat. Phys. Chem. 50 (1997) 179. [11] J. Ramirez-Nino, D. Mendoza, V.M. Castano, Radiat. Meas. 29 (1998) 195. [12] K. Maruszewski, L. Czernicki, W. Waclawek, W. Strek, J. Mol. Struct. 404 (1997) 141.
166
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[13] K. Maruszewski, W. Strek, M. Jasiorski, P. Deren, Z. Ziembik, I. Czerniak, E. Czernia, W. Waclawek, J. Mol. Struct. 519 (2000) 125. [14] R. Litr an, E. Blanco, M. Ramırez-Del-Solar, L. Esquivias, J. Sol– Gel Sci. Technol. 8 (1997) 985.
[15] G.M. Zimina, G.P. Tkhorzhnitskii, D.V. Krasnyi, A.V. Vannikov, High Energ. Chem. 36 (2002) 7. [16] E. Kalecinska, J. Kalecinski, M. Krowicka, Radiat. Phys. Chem. 60 (2001) 169.