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water solutions with high ionic strength
Journal of Molecular Structure 610 (2002) 187±190
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Spectroscopic behavior of 1,1 0-diethyl-2,2 0 -dicarbocyanine iodide in ethanol/water solutions with high ionic strength Krzysztof Maruszewski a,b,*, Marek Jasiorski a, Wiesøaw StreÎk a b
a Institute of Low Temperature and Structure Research, Polish Academy of Sciences, OkoÂlna 2, 50-950 Warsaw, Poland Institute of Materials Sciences and Applied Mechanics, Wrocøaw University of Technology, Smoluchowskiego 25, 50-370 Warsaw, Poland
Received 4 October 2001; revised 18 December 2001; accepted 14 January 2002
Abstract Absorption spectra of 1,1 0 -diethyl-2,2 0 -dicarbocyanine iodide (DDI) have been obtained in ethanol/water mixtures. Increase of ionic strength obtained by addition of salts (e.g. NaCl) to the solvent mixture containing 10% of H2O and 90% of EtOH leads to appearance of a new absorption band at 849 nm. Intensity of this band increases with salt concentration which suggests that this spectral feature is related to a DDI aggregate. However, no emission has been observed with excitation at 850 nm indicating that this feature does not correspond to a J-type aggregate. Addition of NaCl to DDI solutions possessing the EtOH/H2O (v:v) ratio different from 1:9 does not induce appearance of the new absorption band. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Dicarbocyanine; Aggregates; Absorption spectroscopy; Luminescence
1. Introduction Cyanine dyes have attracted considerable attention due to their various applications such as laser dyes [1,2], sensitizers in photographic proccesses [3] or membrane potential probes [4,5]. Some carbocyanines have been recently investigated [6±8] as potential photosensitizers for cancer photodynamic therapy (PDT). Photophysical and chemical properties of carbocyanines are strongly related to their tendency to form aggregates [9±20]ÐH-type (sandwich) molecular assemblies with absorption bands blue-shifted relative to their monomer absorption peaks and J-type (linear) * Corresponding author. Address: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, OkoÂlna 2, 50950 Warsaw, Poland. Tel.: 148-71-343-5021; fax: 148-71-3441029. E-mail address: [email protected] (K. Maruszewski).
aggregates with red-shifted absorption bands and characteristic, narrow emission features. In order to study the aggregation equilibria cyanines have been incorporated into various media such as clays [21], colloidal silica [22], liposomes [23,24], Langmuir±Blodgett ®lms [25] or sol±gel silicate matrices [26]. Results presented in this work suggest a new kind of 1,1 0 -diethyl-2,2 0 -dicarbocyanine iodide (DDI) aggregate occurring in ethanol/water mixtures of which ionic strength have been increased by dissolution of salts.
Absorption spectra of such solutions contain, in addition to regular monomer and H-dimer absorption
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0022-286 0(02)00049-2
188
K. Maruszewski et al. / Journal of Molecular Structure 610 (2002) 187±190
Fig. 1. Electronic absorption spectra of DDI in ethanol (a), 1:1 EtOH/H2O mixture (b) and water (c). Insert presents the DDI emission spectrum obtained in EtOH at 77 K with 700 nm excitation.
Fig. 2. Electronic absorption spectra of DDI in 1:9 EtOH/H2O mixtures containing increasing NaCl concentration. Spectrum in trace A has been obtained for a salt-free DDI solution.
features, a band at 850 nm. The intensity of the new band increases with the increasing salt concentration. However, there has been no luminescence observed with excitation at 850 nm. Thus, the new absorption band does not seem to be related to a J-type agglomerate.
3. Results and discussion
2. Materials and methods DDI and methyl viologen dichloride were purchased from Aldrich and used as received. Ethanol (95%) and NaCl were obtained from Polish Chemicals (POCh). The DDI concentration used in the experiments was 4 £ 10 25 M. Absorption spectra were measured on a Carry spectrophotometer. Emission spectra were recorded on an Ocean Optics SD-2000 spectrophotometer. CW excitations at 700 and 850 nm were obtained from a Surelite Optical Parametric Oscillator (OPO) pumped by third harmonic of a Nd:YAG laser line (1064 nm).
Fig. 1 presents absorption spectra of DDI in ethanol (Trace A), 1:1 ethanol/water mixture (Trace B) and pure water (Trace C). The spectrum obtained in EtOH, according to Razumova and Tarnovskii [27], represents the stable, monomeric, all-trans isomer of the dye. However, the observed bands (at 711 and 653 nm) are broad enough to possibly hide absorption features belonging to photoisomers (cis±trans: 733 and 657 nm; cis±cis: 646 nm [27]). Upon addition of water, the spectrum changes drastically (Trace B) due to formation of H-dimers [12]. The monomer band moves from 711 to 701 nm and two new bands appear at 619 and 591 nm (shoulder). The band at 591 nm could be a vibrational component of the Hdimer electronic transition since the energy difference between the two blue-side bands (619 and 591 nm) equals only 765 cm 21. Another possibility is a presence of two H-dimers of the two different cis± trans DDI isomers. Although DDI does not dissolve well in water, it is
K. Maruszewski et al. / Journal of Molecular Structure 610 (2002) 187±190
possible to obtain aqueous solutions of this dye with vigorous agitation at room temperature. It is interesting to note that in this case (Trace C) the DDI absorption spectrum is virtually identical to that obtained for 1:1 ethanol/water mixture (Trace B). The insert in Fig. 1 presents the DDI emission spectrum obtained in ethanol at 77 K. The exciting laser line lexc 700 nm is labeled with an asterisk. The maximum of the DDI emission occurs at 740 nm and the weaker band at 800 nm belongs to the 0±1 vibronic transition [1]. The dye luminescence maximum measured in glycerol at room temperature is red shifted to approximately 750 nm [1]. Fig. 2 presents electronic absorption spectra of DDI in EtOH/H2O (1:9) mixtures containing increasing amounts of dissolved NaCl. Addition of NaCl results in broadening of the bands assigned to the dye monomer and H-dimer(s) (see Fig. 1) and appearance of the new band at 849 nm. The intensity of this band increases relatively to the other bands with the increasing NaCl concentration. The same effect has been observed when other salts (e.g. methyl viologen dichloride) have been used instead of NaCl. However, it is important to stress that even slight changes in the solvent composition (i.e. alcohol/water ratio) resulted in the absence of the DDI absorption band at 849 nm. It is well known that increase in ionic strength [12] of aqueous solutions of cyanine dyes can lead to enhancement of their J-type aggregation. Such aggregates usually display characteristic, narrow emission following the excitation within the J-absorption band [12,13,19]. However, we have not been able to obtain any emission with excitation at 850 nm (neither at room temperature nor at 77 K). Furthermore, as it has been mentioned earlier, addition of water to ethanol solutions of DDI lowers the dye solubility. Thus, apparently both factors (i.e. the increase in ionic strength and the decrease in solubility) are necessary to cause the appearance of the new spectral feature in the DDI absorption spectrum. This observation suggests that the near-IR absorption band corresponds to agglomerates of a new kind, not reported yet in the literature. On the other hand, it is interesting to note that similar broadening of an absorption band and appearance of a new feature in the near-IR region have been observed for DMSO solutions of magnesium phthalocyanine (MgPc) upon addition of water [28]. In this
189
case (similarly to the EtOH/H2O/NaCl solutions of DDI) addition of water decreases the MgPc solubility. However, in both cases there has not been observed any precipitation of the dyes. Thus, the new absorption features do not seem to belong to the dyes solidstate forms. 4. Conclusions Increase of ionic strength of water/ethanol solutions of DDI results in a signi®cant broadening of the dye absorption envelope and appearance of a new absorption band at approximately 850 nm. This new near-IR feature occurs only in the case of the solutions with a speci®c solvents ratio (1:9 EtOH/H2O). Although DDI does not dissolve well in water, precipitation of the dye in the case of the earlier mentioned solution has not been observed. Thus, the new spectral feature does not belong to the solid-state form of DDI and is probably related to a new form of the dye agglomerate. Since no emission has been observed for the DDI solution under investigation this new agglomerate does not seem to be of the J-type character. Acknowledgements This work was supported by the grant from the Polish Committee for Scienti®c Research (Grant no. KBN 3 T09B 027 18). References [1] M.L. Spaeth, D.P. Bortfeld, Appl. Phys. Lett. 9 (1966) 179. [2] J.C. Mialocq, P. Goujon, M. Arvis, J. Chim. Phys. 76 (1979) 1067. [3] D.M. Sturmer, D.W. Heseltine, in: T.H. James (Ed.), The Theory of Photographic Processes, Fourth ed, Macmillan, New York, 1977 Chapter 8. [4] P.J. Sims, A.S. Waggoner, C. Wang, J.F. Hoffman, Biochemistry 16 (1974) 2215. [5] M. Rees, T.W. Smith, L.B. Chen, Biochemistry 30 (1991) 4480. [6] M. Krieg, R.W. Redmont, Photochem. Photobiol. 57 (1994) 472. [7] M. Krieg, M.B. Srichai, R.W. Redmont, Biochim. Biophys. Acta 1151 (1993) 168. [8] M. Krieg, J.M. Bilitz, M.B. Srichai, R.W. Redmont, Biochim. Biophys. Acta 1199 (1994) 149. [9] G. Scheibe, Angew. Chem. 49 (1936) 563.
190 [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
K. Maruszewski et al. / Journal of Molecular Structure 610 (2002) 187±190 E.E. Jelley, Nature 138 (1936) 1009. W. West, S. Pearce, J. Phys. Chem. 69 (1965) 1894. A.H. Hertz, Photogr. Sci. Engng 18 (1974) 323. C. Honda, H. Hada, Photogr. Sci. Engng 21 (1977) 97. V. SundstroÈm, T. Gillbro, J. Chem. Phys. 83 (1985) 2733. E. Barni, P. Savarino, G. Viscardi, Acc. Chem. Res. 24 (1991) 98. M. Levitus, R.M. Negri, P.F. Aramendia, J. Phys. Chem. 99 (1995) 14231. H. Min, J. Park, J. Yu, D. Kim, Bull. Korean Chem. Soc. 19 (1998) 650. H. Min, Y.N. Kang, J. Park, Bull. Korean Chem. Soc. 19 (1998) 747. I. Struganova, J. Phys. Chem. A 104 (2000) 9670. A.K. Chibisov, S.V. Shvedov, H. GoÈrner, J. Photochem. Photobiol. A 141 (2001) 39. M. Iwasaki, M. Kita, K. Ito, A. Kohno, K. Fukunishi, Clays Clay Min. 48 (2000) 392.
[22] S.Y. Chen, M.L. Horng, E.L. Quitevis, J. Phys. Chem. 93 (1989) 3683. [23] T. Sato, M. Kurahashi, Y. Yonezawa, Langmuir 9 (1993) 3395. [24] K. Maruszewski, A. Sidorowicz, A. Poøa, W. StreÎk, J. Mol. Struct. 444 (1998) 147. [25] V.A. Tkachev, A.V. Tolmachev, L.V. Chernigov, E.E. Lakin, Ukrainskii Fizicheskii Zhur. 38 (1993) 1220. [26] K. Maruszewski, A. Sidorowicz, A. Ulatowska, H. Podbielska, W. StreÎk, J. Mol. Struct. 450 (1998) 193. [27] T.K. Razumova, A.H. Tarnovskii, Optics Spectrosc. 78 (1995) 56. [28] K. Maruszewski, W. StreÎk, M. Jasiorski, P. DerenÂ, Z. Ziembik, I. Czerniak, E. Czernia, W. Wacøawek, J. Mol. Struct. 519 (2000) 125.
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Spectroscopic behavior of 1,1 0-diethyl-2,2 0 -dicarbocyanine iodide in ethanol/water solutions with high ionic strength Krzysztof Maruszewski a,b,*, Marek Jasiorski a, Wiesøaw StreÎk a b
a Institute of Low Temperature and Structure Research, Polish Academy of Sciences, OkoÂlna 2, 50-950 Warsaw, Poland Institute of Materials Sciences and Applied Mechanics, Wrocøaw University of Technology, Smoluchowskiego 25, 50-370 Warsaw, Poland
Received 4 October 2001; revised 18 December 2001; accepted 14 January 2002
Abstract Absorption spectra of 1,1 0 -diethyl-2,2 0 -dicarbocyanine iodide (DDI) have been obtained in ethanol/water mixtures. Increase of ionic strength obtained by addition of salts (e.g. NaCl) to the solvent mixture containing 10% of H2O and 90% of EtOH leads to appearance of a new absorption band at 849 nm. Intensity of this band increases with salt concentration which suggests that this spectral feature is related to a DDI aggregate. However, no emission has been observed with excitation at 850 nm indicating that this feature does not correspond to a J-type aggregate. Addition of NaCl to DDI solutions possessing the EtOH/H2O (v:v) ratio different from 1:9 does not induce appearance of the new absorption band. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Dicarbocyanine; Aggregates; Absorption spectroscopy; Luminescence
1. Introduction Cyanine dyes have attracted considerable attention due to their various applications such as laser dyes [1,2], sensitizers in photographic proccesses [3] or membrane potential probes [4,5]. Some carbocyanines have been recently investigated [6±8] as potential photosensitizers for cancer photodynamic therapy (PDT). Photophysical and chemical properties of carbocyanines are strongly related to their tendency to form aggregates [9±20]ÐH-type (sandwich) molecular assemblies with absorption bands blue-shifted relative to their monomer absorption peaks and J-type (linear) * Corresponding author. Address: Institute of Low Temperature and Structure Research, Polish Academy of Sciences, OkoÂlna 2, 50950 Warsaw, Poland. Tel.: 148-71-343-5021; fax: 148-71-3441029. E-mail address: [email protected] (K. Maruszewski).
aggregates with red-shifted absorption bands and characteristic, narrow emission features. In order to study the aggregation equilibria cyanines have been incorporated into various media such as clays [21], colloidal silica [22], liposomes [23,24], Langmuir±Blodgett ®lms [25] or sol±gel silicate matrices [26]. Results presented in this work suggest a new kind of 1,1 0 -diethyl-2,2 0 -dicarbocyanine iodide (DDI) aggregate occurring in ethanol/water mixtures of which ionic strength have been increased by dissolution of salts.
Absorption spectra of such solutions contain, in addition to regular monomer and H-dimer absorption
0022-2860/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0022-286 0(02)00049-2
188
K. Maruszewski et al. / Journal of Molecular Structure 610 (2002) 187±190
Fig. 1. Electronic absorption spectra of DDI in ethanol (a), 1:1 EtOH/H2O mixture (b) and water (c). Insert presents the DDI emission spectrum obtained in EtOH at 77 K with 700 nm excitation.
Fig. 2. Electronic absorption spectra of DDI in 1:9 EtOH/H2O mixtures containing increasing NaCl concentration. Spectrum in trace A has been obtained for a salt-free DDI solution.
features, a band at 850 nm. The intensity of the new band increases with the increasing salt concentration. However, there has been no luminescence observed with excitation at 850 nm. Thus, the new absorption band does not seem to be related to a J-type agglomerate.
3. Results and discussion
2. Materials and methods DDI and methyl viologen dichloride were purchased from Aldrich and used as received. Ethanol (95%) and NaCl were obtained from Polish Chemicals (POCh). The DDI concentration used in the experiments was 4 £ 10 25 M. Absorption spectra were measured on a Carry spectrophotometer. Emission spectra were recorded on an Ocean Optics SD-2000 spectrophotometer. CW excitations at 700 and 850 nm were obtained from a Surelite Optical Parametric Oscillator (OPO) pumped by third harmonic of a Nd:YAG laser line (1064 nm).
Fig. 1 presents absorption spectra of DDI in ethanol (Trace A), 1:1 ethanol/water mixture (Trace B) and pure water (Trace C). The spectrum obtained in EtOH, according to Razumova and Tarnovskii [27], represents the stable, monomeric, all-trans isomer of the dye. However, the observed bands (at 711 and 653 nm) are broad enough to possibly hide absorption features belonging to photoisomers (cis±trans: 733 and 657 nm; cis±cis: 646 nm [27]). Upon addition of water, the spectrum changes drastically (Trace B) due to formation of H-dimers [12]. The monomer band moves from 711 to 701 nm and two new bands appear at 619 and 591 nm (shoulder). The band at 591 nm could be a vibrational component of the Hdimer electronic transition since the energy difference between the two blue-side bands (619 and 591 nm) equals only 765 cm 21. Another possibility is a presence of two H-dimers of the two different cis± trans DDI isomers. Although DDI does not dissolve well in water, it is
K. Maruszewski et al. / Journal of Molecular Structure 610 (2002) 187±190
possible to obtain aqueous solutions of this dye with vigorous agitation at room temperature. It is interesting to note that in this case (Trace C) the DDI absorption spectrum is virtually identical to that obtained for 1:1 ethanol/water mixture (Trace B). The insert in Fig. 1 presents the DDI emission spectrum obtained in ethanol at 77 K. The exciting laser line lexc 700 nm is labeled with an asterisk. The maximum of the DDI emission occurs at 740 nm and the weaker band at 800 nm belongs to the 0±1 vibronic transition [1]. The dye luminescence maximum measured in glycerol at room temperature is red shifted to approximately 750 nm [1]. Fig. 2 presents electronic absorption spectra of DDI in EtOH/H2O (1:9) mixtures containing increasing amounts of dissolved NaCl. Addition of NaCl results in broadening of the bands assigned to the dye monomer and H-dimer(s) (see Fig. 1) and appearance of the new band at 849 nm. The intensity of this band increases relatively to the other bands with the increasing NaCl concentration. The same effect has been observed when other salts (e.g. methyl viologen dichloride) have been used instead of NaCl. However, it is important to stress that even slight changes in the solvent composition (i.e. alcohol/water ratio) resulted in the absence of the DDI absorption band at 849 nm. It is well known that increase in ionic strength [12] of aqueous solutions of cyanine dyes can lead to enhancement of their J-type aggregation. Such aggregates usually display characteristic, narrow emission following the excitation within the J-absorption band [12,13,19]. However, we have not been able to obtain any emission with excitation at 850 nm (neither at room temperature nor at 77 K). Furthermore, as it has been mentioned earlier, addition of water to ethanol solutions of DDI lowers the dye solubility. Thus, apparently both factors (i.e. the increase in ionic strength and the decrease in solubility) are necessary to cause the appearance of the new spectral feature in the DDI absorption spectrum. This observation suggests that the near-IR absorption band corresponds to agglomerates of a new kind, not reported yet in the literature. On the other hand, it is interesting to note that similar broadening of an absorption band and appearance of a new feature in the near-IR region have been observed for DMSO solutions of magnesium phthalocyanine (MgPc) upon addition of water [28]. In this
189
case (similarly to the EtOH/H2O/NaCl solutions of DDI) addition of water decreases the MgPc solubility. However, in both cases there has not been observed any precipitation of the dyes. Thus, the new absorption features do not seem to belong to the dyes solidstate forms. 4. Conclusions Increase of ionic strength of water/ethanol solutions of DDI results in a signi®cant broadening of the dye absorption envelope and appearance of a new absorption band at approximately 850 nm. This new near-IR feature occurs only in the case of the solutions with a speci®c solvents ratio (1:9 EtOH/H2O). Although DDI does not dissolve well in water, precipitation of the dye in the case of the earlier mentioned solution has not been observed. Thus, the new spectral feature does not belong to the solid-state form of DDI and is probably related to a new form of the dye agglomerate. Since no emission has been observed for the DDI solution under investigation this new agglomerate does not seem to be of the J-type character. Acknowledgements This work was supported by the grant from the Polish Committee for Scienti®c Research (Grant no. KBN 3 T09B 027 18). References [1] M.L. Spaeth, D.P. Bortfeld, Appl. Phys. Lett. 9 (1966) 179. [2] J.C. Mialocq, P. Goujon, M. Arvis, J. Chim. Phys. 76 (1979) 1067. [3] D.M. Sturmer, D.W. Heseltine, in: T.H. James (Ed.), The Theory of Photographic Processes, Fourth ed, Macmillan, New York, 1977 Chapter 8. [4] P.J. Sims, A.S. Waggoner, C. Wang, J.F. Hoffman, Biochemistry 16 (1974) 2215. [5] M. Rees, T.W. Smith, L.B. Chen, Biochemistry 30 (1991) 4480. [6] M. Krieg, R.W. Redmont, Photochem. Photobiol. 57 (1994) 472. [7] M. Krieg, M.B. Srichai, R.W. Redmont, Biochim. Biophys. Acta 1151 (1993) 168. [8] M. Krieg, J.M. Bilitz, M.B. Srichai, R.W. Redmont, Biochim. Biophys. Acta 1199 (1994) 149. [9] G. Scheibe, Angew. Chem. 49 (1936) 563.
190 [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
K. Maruszewski et al. / Journal of Molecular Structure 610 (2002) 187±190 E.E. Jelley, Nature 138 (1936) 1009. W. West, S. Pearce, J. Phys. Chem. 69 (1965) 1894. A.H. Hertz, Photogr. Sci. Engng 18 (1974) 323. C. Honda, H. Hada, Photogr. Sci. Engng 21 (1977) 97. V. SundstroÈm, T. Gillbro, J. Chem. Phys. 83 (1985) 2733. E. Barni, P. Savarino, G. Viscardi, Acc. Chem. Res. 24 (1991) 98. M. Levitus, R.M. Negri, P.F. Aramendia, J. Phys. Chem. 99 (1995) 14231. H. Min, J. Park, J. Yu, D. Kim, Bull. Korean Chem. Soc. 19 (1998) 650. H. Min, Y.N. Kang, J. Park, Bull. Korean Chem. Soc. 19 (1998) 747. I. Struganova, J. Phys. Chem. A 104 (2000) 9670. A.K. Chibisov, S.V. Shvedov, H. GoÈrner, J. Photochem. Photobiol. A 141 (2001) 39. M. Iwasaki, M. Kita, K. Ito, A. Kohno, K. Fukunishi, Clays Clay Min. 48 (2000) 392.
[22] S.Y. Chen, M.L. Horng, E.L. Quitevis, J. Phys. Chem. 93 (1989) 3683. [23] T. Sato, M. Kurahashi, Y. Yonezawa, Langmuir 9 (1993) 3395. [24] K. Maruszewski, A. Sidorowicz, A. Poøa, W. StreÎk, J. Mol. Struct. 444 (1998) 147. [25] V.A. Tkachev, A.V. Tolmachev, L.V. Chernigov, E.E. Lakin, Ukrainskii Fizicheskii Zhur. 38 (1993) 1220. [26] K. Maruszewski, A. Sidorowicz, A. Ulatowska, H. Podbielska, W. StreÎk, J. Mol. Struct. 450 (1998) 193. [27] T.K. Razumova, A.H. Tarnovskii, Optics Spectrosc. 78 (1995) 56. [28] K. Maruszewski, W. StreÎk, M. Jasiorski, P. DerenÂ, Z. Ziembik, I. Czerniak, E. Czernia, W. Wacøawek, J. Mol. Struct. 519 (2000) 125.