Metal-Containg and Metallosupramilecular Polymers and Materials

Chapter 31

Spectroscopic and Liquid Crystal Properties of Phthalocyanine Macromolecules with Biomedical Applications Ernie H. G. Langner, Wade L. Davis, Rebotsamang F. Shago, and Jannie C. Swarts

Downloaded by UNIV OF ARIZONA on August 9, 2012 | http://pubs.acs.org Publication Date: March 23, 2006 | doi: 10.1021/bk-2006-0928.ch031

*

Department of Chemistry, University of the Free State, Nelson Mandela Drive, Bloemfontein 9300, South Africa

The influence of alkyl substituent chain length, peripheral versus non-peripheral substitution positions, and coordinated central metal (2H, Cu , Ni , Zn and Cl-Al ) on mesophase behaviour and spectroscopic properties of phthalocyanine complexes are described 2+

© 2006 American Chemical Society

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In Metal-Containing and Metallosupramolecular Polymers and Materials; Schubert, U., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

444

Background 1

Phthalocyanines are used industrially as blue and green pigments. Other areas of phthalocyanine study include their application as non-linear optical materials, as catalysts in a variety of chemical reactions including oxidations of mercaptans and hydrogénation of multiple bonds, as converters of solar energy to other forms of energy and as photodynamic cancer drugs. As photodynamic cancer drugs, phthalocyanines have many intrinsic advantageous over porphyrins such as photophrin, the first porphyrin approved for photodynamic cancer therapy in die United States. Phthalocyanines are attractive as photodynamic cancer drugs because of the wavelength at which they absorb red or infrared light, and the efficiency by which they do so. Light of wavelength 630 nm or longer (i.e. red or infrared light) penetrates deepest through body tissue. The Q-band peak maximum for most metallated phthalocyanines is at 660 nm or longer, a wavelength range that is especially suitable for photodynamic cancer therapy. The most intense light absorbtion for photophrin is observed in the 400 nm Soret band range, while the Q-band absorbtion between 500 and 650 nm are much less intense (s 30nm 3500 dm m o l cm" ). In contrast, extinction coefficients associated with the Q-band of phthalocyanines are large; sometimes exceeding 200 000 dm mol" cm" . The coordinated metal determines the success of phthalocyanines in photodynamic cancer therapy. The photophysics of zinc and aluminium phthalocyanines are among those best suited for photodynamic cancer therapy. Different coordinated metals, however, have almost no influence on the wavelength at which complexes absorb light. Limitations of phthalocyanines as photodynamic cancer drugs are nested in their notorious insolubility and the loss of optimum quantum yields upon radiation due to aggregation. To overcome both these issues, researchers substitute bulky substituents on the phthalocyanine macrocycle. Linear long chain alkyl substituents enhance organic solubility and lower aggregation, and Cook has demonstrated that C and C non-peripheral octa-alkylated zinc phthalocyanines have photodynamic cancer activity. In an alternative approach, Van Lier demonstrated that peripheral sulphonated aluminium phthalocyanines posess aqueous solubility as the sodium salts. Another possibility in enhancing aqueous solubility of phthalocyanine macrocycles, is to make use of watersoluble polymeric drug carriers, as demonstrated for some ferrocene derivatives. The introduction of long chain linear alkyl substituents and mixtures of peripheral and non-peripheral substituents impose interesting physical properties on phthalocyanine macrocycles. These include less aggregation than that observed for short chain substituents, liquid crystalline properties and 2

3

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7

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_ 1

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1 0

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differences in the wavelength where Q-band peak absorbtion is observed. Phthalocyanine liquid crystal phases are normally discotic columnar. Interactions between the aromatic macrocyclic cores maintain columnar packing, while melted long side chains provide columnar mobility. Up to three different mesophases have thus far been reported for phthalocyanine liquid crystals. Higher temperature mesophases normally has a disordered hexagonal symmetry, while relative lower temperature mesophases have been found to be either of hexagonal or rectangular symmertry. 13,

1 5

15


Objective The objective of this study was to determine the effect chain length and substitution position have on the liquid crystalline properties of alkylated and ferrocene-containing alkoxylated phthalocyanines with 2 H , Z n , C u , N i and C l - A l * coordinated in the macrocyclic cavity by variable temperature optical microscopy and differential scanning calorimetric techniques. A UV-vis spectroscopic study also demonstrated the relationship between Q-band peak maxima and degree of non-peripheral substitution (as compared to peripheral substitution). +

2+

2+

2 +

3

Experimental Materials. A l l reagents were used without further purification. Dichloromethane was refluxed over calcium hydride and freshly distilled prior to use. Phthalocyanines without metallocene side chains were synthesized as described ' * before. 9 l6

17

Synthesis of phthalocyanines with ferrocenylalkoxy side chains. The synthesis of 1,4,8,11,15,18-hexa(tetradecyl)-23-(4-ferrocenylbutoxy) phthalocyanine may serve as an example: 3,6-Di(tetradecyl)phthalonitrile (0.940 g, 1.804 mmol) and 4-(4-ferrocenylbutoxy)phthalonitrile (0.090 g, 0.256 mmol) were dissolved in warm (80 °C) pentanol (12 cm ). A n excess of clean lithium metal (0.2 g, 0.0288 mol) was added in small portions and the mixture was heated thereafter for 16 hours at 110 °C. The cooled, deep green suspension was stirred with acetone (20 cm ), the solution was filtered and the solids washed with acetone (50 cm ) before the combined acetone solutions were concentrated 18

3

3

3


446 3

3

to ca. 20 cm . Acetic acid (20 cm ) was added and the heterogeneous mixture stirred for 30 minutes and the precipitated collected to afford the crude product (0.320 g) after recrystallisation from THF/methanol. The crude product was chromatographed on silica gel at different ratios of hexane/toluene as eluents. Three fractions could be clearly separated and identified. They were isolated and recrystalized from THF/methanol. The first fraction was recovered from the column with hexane/toluene (20:1), and was identified as 1,4,8,11,15,18,22,25octa(tetradecyl)phthalocyanine (58 mg, 10.70 %, R = 0.99). The second fraction isolated with hexane/toluene as mobile phase in a 20:3 ratio, and was identified as 1,4,8,11,15,18-hexa(tetradecyl)-23-(4-ferrocenylbutoxy)phthalocyanine ( 38.3 mg, 6.16 %, R = 0.48); 6 (CDC1 ); 0.87 (18 H , t, 6 χ C H ) , 1.27 (132 H , m, 6 χ -(CH )„-), 1.93 (2H, m, 1 χ (-CH -CH -CH -CH2-Fc)), 2.18 (14 H , m, 1 χ (C H - C H -CH -CH -Fc), 6 χ (Ar-CH -CH -)), 2.60 (2 H , m, 1 χ 0 - C H - C H C H - C H - F c ) , 4.18 (14 H , m , l χ ( - C H - C H - C H - C H - F c ) , 6 χ ( A r - C H - C H - ) , 4.44 (9 H , m, C , H ) , 7.50 (1 H , d, Ar-H), 7.82 (6 H , m, 3 χ Ar-H ), 8.38 (1 H , s, Ar-H), 8.82 (1 H , d, Ar-H). The third fraction isolated with hexane/toluene (20:5) and was identified as tetra(tetradecyl)-di(ferrocenylbutoxy)phthalocyanine (7.10 mg, 1.51%, R = 0.19); 6 (CDC1 ); 0.80 (12 H , t, 4 χ C H ) , 1.24 (88 H , m, 4 χ -(CH )„-), 1.79 (4 H , m, 2 χ (-CH -CH -CH -CH -Fc)), 1.98 (4H, m, 2 χ (C H - C H - C H - C H - F c ) , 2.17 (8 H , m, 4 χ (Ar-CH -CH -)), 2.64 (4 H , m, 2 χ OC H - C H -CH -CH -Fc), 4.00 - 4.60 (30 H , m, 2 χ ( - C H - C H - C H - C H - F c ) , 4 χ ( A r - C H - C H - ) , 2 χ C H ) , 7.4 - 8.9 (10 H , m, 2 χ A r - H , 2 χ Ar-H ). f

f

H

3


2

2

2

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2

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Metallation experiments. Phthalocyanine retaliations were performed following the general procedures described in references 9 and 19. Instrumentation and Techniques. Proton NMR-spectra at 298 Κ were recorded at 300 M H z on a Broker Advance D P X 300 N M R spectrometer, chemical shifts are referenced to SiMe at 0.00 ppm. Solution electronic spectra were recorded in T H F or cyclohexane on a Varian Cary 50 UV-vis dual beam spectrophotometer at 298 K . Phase transitions between crystal, liquid crystal and isotropic-liquid states were monitored by DSC (for enthalpy changes, ca. 7 mg samples at heating and cooling rate of 10 °C min" between -70 °C and a convenient maximum temperature at least 30 °C higher than the melting point of the compounds were used) on a T A Instruments D S C 10 thermal analyser fitted with a Du Pont Instruments mechanical cooling accessory and a T A Instruments Thermal Analyst 2000 data processing unit. To obtain accurate transition temperatures, visual measurements were performed on an Olympus BH-2 polarising microscope in conjunction with a Linkam T M S 92 thermal analyser with a Linkam T H M 600 cell. The heating and cooling rates used were either 5 °C min" o r 2 ° C min" . 4

1

1


1

447

Results & Discussion

Synthesis and UV-vis spectroscopy Metal-free and metallated phthalocyanines were synthesised as shown in Scheme 1. The reaction involves cyclisation of four phthalonitrile molecules to obtain the octa-aza phthalocyanine macrocycle. The C l - A l phthalocyanines were obtained directly from the condensation of 3,6-didecyldiimino-isoindoline in the presence of A1C1 . 20


3

CH.CH.CH,

Scheme 1. Cyclisation of3,6-dialkylatedphthalonitriles leads to non-peripheral substituted metal-free phthalocyanines. Shown above is 1,4,8,11, IS, 18,22,25octa(pentadecyl)phthalocyanine. Metal insertion with M(CH COO) , M = Cu , Ni * or Zn *, are facile, high yielding reactions. Interactions between aromatic phthalocyanine cores maintain a columnar packed mesophase, while melted long side chains allow columnar mobility. 2+

3

2

2

2

Normally, one would expect alkyl groups to align in a linear fashion in the plane of the phthalocyanine macrocyclic core. However, the flat structure of the phthalocyanine macrocycle causes non-peripheral substituents to collide. Hence, Cook showed in a crystal structure of the C compound that six of the eight side chains of non-peripheral octa-hexylated phthalocyanines are orientated in the plane of the macrocycle, pointing away from it. Four of these have their 21

6


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C-C bonds staggered in the macrocyclic plane, while two are staggered out of the plane and make a sharp turn at the first C-atom adjacent to the macrocyclic core to minimise steric hindrance. The remaining two hexyl groups make an immediate sharp turn at the first C-atom to align themselves approximately perpendicular to the plane of the macrocyclic core. In the solid state, they act as spacers between two adjacent macrocycles. Figure 1 shows the Soret and Q-bands in the UV-vis spectra of the nonperipheral substituted compounds 1,4,8,11,15,18,22,25-octa(dodecyl)phthalocyanine (the Q-band shows two peaks with peak maxima at 730 and 700 nm), 1,4,8,11,15,18,22,25-octa(dodecyl)phthalocyaninatozinc(II) (the Q-band is a single peak with peak maxima at 700 nm), and the peripheral substituted tetra(Wyl)-phthalocyaninatocobalt(II) which shows a single Q band peak maximum at 660 nm. Moving from peripheral to non-peripheral substituted metal-containing phthalocyanines leads to a red shift of 40 nm in Q-band peak maximum. The switch from a cobalt to zinc complex was not the reason for this shift as different coordinated metals have almost no influence on the wavelength at which complexes absorb light. 250000 S 200000 -j \

150000 H

s ω

100000 50000

250 350 450 550 650 750 850 wavelength / nm Figure 1. UV-vis spectra of1,4,8,1 l,15,18,22,25-octa(dodecyl)phthalocyanine (solid line), its zinc complexf), and the peripheral substituted complex tetra(butyl)phthalocyaninatocobalt(U) (- - -).

Metal-free and metallated phthalocyanines differ in having D u and D symmetry and this is manifested in differences especially in the Q-band region. The Q-band twin peak of the metal-free system converges into a single peak when a metal is inserted in the phthalocyanine because metal insertion leads to a degeneracy of the phthalocyanine's lowest energy singlet state. By increasing the alkyl chain length of the non-peripheral substituents on the phthalocyanines, less aggregation is observed. Aggregation manifests in 2


4h


449 deviations from the Beer-Lambert law. Without any aggregation, a linear dependence exists between phthalocyanine concentration and absorbance. Deviations from this linear relationship indicate aggregation of the flat macrocyclic molecules. Aggregation involves the stacking of phthalocyanines on top of each other much like a deck of cards. Thus, aggregated phthalocyanine molecules do not exist independently of each other in solution, and the different degrees of association in these non-ideal solutions lead to deviations from the Beer-Lambert law. Figure 2 demonstrates the validity of the Beer-Lambert law for the Q-band of non-aggregated solutions of 1,4,8,11,13,18,22,25-octa(dodecyl)phthalocyanine derivatives as well as the concentration at which aggregation sets in for 1,4,8,11,15,18,22,25-octa(alkylated)phthalocyaninatozinc(II) complexes with different alkyl chain lengths.

Figure 2. Left: The Beer-Lambert law, A = eel, for 1,4,8,11,15,18,22,25octa(decyl)phthalocyanine at 730 nm (- - -) andfor 1,4,8,11,15,18,22,25octa(decyl)phthalocyaninatozinc(U) at 700 nm (—) in THF at 25 °C. Right. The concentration where the Beer-Lambert law breaks down for 1,4,8,11,15,18,22,25-octa(alkylated)phthalocyaninatozinc(H) complexes dissolved in cyclohexane at 18 °C.

O f special importance is the observation that from an alkyl substituent chain length of Cio, the onset concentration of aggregation suddenly begins to increase dramatically. This is consistent with a view that, as in the solid state, separation of the phthalocyanine macrocycles by their own side chains, or even encapsulation of the macrocyclic core in its own side chains, is possible in solution, provided the substituents are long enough.


450 Phthalocyanines with ferrocenylalkoxy side chains were synthesised as shown in Scheme 2. The statistical condensation using a mixture of two different phthalonitriles invariably gives an entire range of different phthalocyanines designated as A A A A , A A A B , A A B B , A B A B , A B B B and BBBB. In these acronyms, A represents a fragment o f the macrocycle that originated from a 3,6-dialkylated phthalonitrile and Β represents a fragment that originated from a 4-alkoxylated phthalonitrile bearing a terminal ferrocenyl group on the alkoxy chain. The ratio of 9:1 for reacting phthalonitriles A : B was chosen because this allowed a substantial yield of the A A A B product while minimising the products A A B B , A B A B , A B B B and B B B B . The B-fragment can condense in one of two configurations during phthalocyanine formation. This leads to a number of regio-structural isomers. The different phthalocyanine products having different numbers of 3-ferrocenylpropyloxy side chains were all separated from each other by intensive column chromatography, but the regio-structural isomers of each product could not be separated. Neither could the regio-isomeric products having general structure A A B B and A B A B be separated from each other. The structures of all the products that can be obtained during this type of statistical condensation are shown in Figure 3.


16

KHiiC^i-ZHPc-O-iCHih-Fel - A A A B

|(H,,C ) -Zn*-0-(CH,)j-Fc| ie

e

+AAAA + A B A B • A A B B + A B B B + B B B B

Scheme 2. Syntheses ofphthalocyanines having non-peripheral alkyl substituents and a peripheral 3- ferrocenylpropyloxy side chain. The choice of mixing the two reacting phthalonitriles in a ratio of 9:1 allowed isolation of AAAA and AAAB as the main reaction products. The UV-vis spectra of each ferrocene-containing product showed the sharp single peak associated with metallated phthalocyanines, or the twin peaks associated with metal-free phthalocyanines. The peak maxima of each product, however, did become more blue-shifted (i.e. peak maxima shifted to shorter wave lengths) as more peripheral side chains were introduced into each product. This blue shift is demonstrated in Figure 3 below.



451

Figure 3. The different metal-free products arisingfrom the reaction between 3,6-di(decyl)phthalonitrile and 4-alkoxyphthalonitriles having a ferrocenyl group on the terminal position. Most products are also regio-isomers. The Qband in the UV-vis spectra for the all non-peripheral Cj alkyl-substituted metal-free (—) and zinc-containing phthalocyanine (- - -) is shown in the middle. The manner in which the various peak maxima shift to shorter wave lengths with increasing amount of non-peripheral substituents is shown on top in the centre. The broken line is associated with the single peak of the zinccontaining derivative, while the two solid lines are associated with the two maximums of the two Q-band peaks of the metal-free phthalocyanines. 0

Phase Studies Phase studies on the present compounds of study were performed utilizing differential scanning calorimetry. Shown below (Figure 4) is a DSC trace for 1,4,8,11,15,18,22,25-octa(tetradecyl)phthalocyaninatozinc(II). Four meso phases were detected between the clearing point (conversion of mesophase to 18


452 isotropic liquid) at 192 °C on the heating cycle and the melting point (transition from a mesophase to a crystalline solid) at 64 °C on the cooling cycle. The longer alkyl substituents showed more mesophase transitions than compounds having shorter chain substituents, with four the largest amount of observed mesophases. In this work each discotic mesophase is labelled D D , D or D with D | assigned to the mesophase arising from the transition between isotropic liquid to the first observed (i.e. highest temperature) mesophase.


b

2

3

4

temperature (°C) Figure 4. Differential scanning calorimetry thermogram of heatflowversus temperature of 1,4,8,11,15,18,22,25-octa(tetradecyl)phthalocyaninatozinc(II). A heating and cooling rate of 10 °C per minute were used. The temperature at which the phase change occurs and the phase change enthalpy associated with it is indicated at each peak.

The temperature range in which the present complexes exhibited mesophase behavior was found to be dependent on three variables: a) The type of metal coordinated in the macrocyclic cavity b) The type (alkyl or ferrocene-containing alkoxy) and position of substitution (peripheral or non-peripheral) for each substituent. c) The length of each side chain, here C - C i . Figure 5 shows the temperature range in which non-peripheral octadecyl substituted phthalocyanines exhibit mesophase behaviour as a function of the coordinated metals C u , 2 H (metal free), N i , C1-A1 and Z n . It is apparent that zinc stabilizes the mesophases of the compounds of this study over the widest temperature range, while nickel is the least effective metal for liquid crystal stabilization. 5

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247 °C

(Fc)2H1

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9. Ο CIAI ο -5 Downloaded by UNIV OF ARIZONA on August 9, 2012 | http://pubs.acs.org Publication Date: March 23, 2006 | doi: 10.1021/bk-2006-0928.ch031

Ni

2Η 0

50

100 150 200 250 300

Liquid crystal temp, range /°C

Figure 5. Bottom 5 bars: Temperature range in which 1,4,8,11,15,18,22,25octa(decyl)phthalocyaninato complexes exhibit liquid crystal behaviour as a function of coordinated metal Top two bars: Liquid crystal temperature range for two complexes in which the two non-peripheral decyl substituents in positions 22 and 25 has been replaced with a single peripheral 3ferrocenylpropyloxy substituent in position 23. The numbers next to each bar represent the temperature difference between the melting and clearing point.

Replacement of two of the non-peripheral decyl substituents on an annulated benzene ring with a peripheral 3-ferrocenylpropyloxy substituent increased the temperature range in which these phthalocyanines exhibited liquid crystal behaviour dramatically. In the case of the metal-free complex, mesophase behaviour was observed over a 167 °C temperature range. This temperature range is 167 - 56 = 111 °C wider than for the non-ferrocene-containing compound. The increase observed for the zinc complex was (accidently) also 111 °c. The effect of alkyl side-chain length on the temperature range in which the phthalocyanines exhibited mesophase behaviour is shown in Figure 6 for the metal-free and zinc complexes. Two key observations can be made. The first is that C is, in the case of the zinc complexes, the shortest alkyl chain length that can support mesophase behaviour. The second is that the C substituent provides the largest temperature range for mesophase behaviour. The mesophase temperature range increases steadily with increasing side chain length s

l2


454 until it reaches for the Z n C | complex a maximum: from 60 to 205.6 °C, that is 145.6 °C. It then decreases again steadily to values of 126 °C for the Z n C species, 110.9 °C for the Z n C | and 94.6 °C for the Z n C species. This decrease in mesophase temperature range is attributed to the wax-like properties of very long alkyl groups that begins to dominate over the columnar discotic liquid crystalline properties of the phthalocyanine complexes. 2

!4

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18

9

2HPc(alkyl) Downloaded by UNIV OF ARIZONA on August 9, 2012 | http://pubs.acs.org Publication Date: March 23, 2006 | doi: 10.1021/bk-2006-0928.ch031

8

ZnPc(aIkyl)

8

υ ρ

2 4 6 8 10 12 14 16 18

2 4 6 8 10 12 14 16 18

number of carbon atoms in the alkyl chain Figure 6. Comparison of the effect alkyl substituent chain length has on temperature range in which metal-free and zinc phthalocyanines exhibit mesophase behaviour. The bottom line represents the temperature at which the crystalline solid to mesophase transition occurs, while the top line shows the temperature at which the mesophase converts to an isotropic liquid. The dots show some of the transitions of one mesophase to another. The numbers represent molar phase transition enthalpies in units of kJ/mol.

The introduction of 3-ferrocenylpropyloxy side chains to the phthalocyanine macrocyclic core have enabled us to produce phthalocyanine materials that have liquid crystalline properties at high temperatures (290 °C for the C j alkyl compound series). The lower temperature limit that supports mesophase behaviour is, however, still above room temperature. The search is in progress to find phthalocyanine materials that exhibit mesophase behaviour well below room temperature. Although the present compounds are well soluble in organic media, they are totally insoluble in aqueous media. This makes them less ideal in a photodynamic cancer therapy application. To overcome this, a research 0


455 effort is also in progress to covalently bind these phthalocyanine complexes to water-soluble, polymeric drug carriers.


Conclusions From this ongoing work, it has been found that non-peripheral alkyl substituted phthalocyanines has liquid crystal properties that are dependent on the length of the alkyl side chain. The type of metal coordinated in the macrocyclic cavity has a large influence on the temperature range in which each phthalocyanine complex exhibits mesophase behaviour. Zinc was the cation that supported mesophase behaviour over the largest temperature range. B y introducing a 3-ferrocenylpropyloxy side-chain in a peripheral position, mesophase behaviour was observed over much larger temperature ranges. Introduction of peripheral side chains caused the peak maxima of the Q-band in the UV-vis spectra of the phthalocyanines to become shifted to shorter wave lengths. The extent of blue shifting increased with increasing amount of peripheral substituents.

Acknowledgments This research was supported by the National Research Foundation of South Africa, the Medical Research Council of South Africa as well as by the University of the Free State. W L D and RFS acknowledge the Mellon Foundation for financial support. The authors also acknowledge Prof. M . J. Cook from the University of East Anglia, U K , for access to his differential scanning calorimetry equipment.

References 1. 2. 3. 4. 5.

Kasuga, K.; Tsutsui, M. Coord. Chem. Rev. 1980, 32, 67. De la Torre, G.; Vazquez, P.; Agullo-Lopez, F.; Torres, T. J. Mater. Chem. 1998, 8, 1671. Buck, T.; Wöhrle, D.; Schulz-Ekloff, G . ; Andreef, A . J. Mol. Catal. 1991, 70, 259. Eckert, H . ; Kiesel, Y . Angew. Chem., Int. Ed. Engl. 1981, 20, 473. Wöhrle, D.; Schlettwein, D.; Kischenmann, M.; Kaneko, M.; Yamada, A. J. Macromol. Sci. Chem. 1990, A27, 1239; Eichhorn, H . J. Porphyrins Phthalocyanines 2000, 4, 88; Wöhrle, D.; Meissner D. Adv. Mater. 1991, 3, 129.


456 6. 7. 8. 9. 10.


11. 12. 13. 14. 15.

16. 17. 18. 19. 20. 21.

A l i , H ; Van Lier J. E. Chem. Rev. 1999, 99, 2379. MacDonald, I. J.; Dougherty, T. J. J. Porphyrins Phthalocyanines. 2001, 5, 105. Allen C. M.; Sharman, W. M.; Van Lier, J. E. J. Porphyrins Phthalocyanines. 2001, 5, 161. Swarts J. C.; Langner, E. H . G.; Krokeide-Hove, N.; Cook, M. J. J. Mater. Chem. 2001, 11, 434. Fabris, C.; Ometto, C.; Milanesi, C.; Jori, G.; Cook, M. J.; Russel, D . A. J. Photohem. Photobiol. B: Biol. 1997, 39, 279; Ometto, C.; Fabris, C.; Milanesi, C.; Jori, G.; Cook, M. J.; Russel, D. A . Br. J. Cancer 1996, 74, 1891. Swarts, J. C.; Swarts, D. M.; Maree, D. M.; Neuse, E. W; L a Madeleine, C.; Van Lier J. E. Anticancer. Res. 2001, 21, 2033. Cook, M. J.; Chambrier, I.; Cracknell, S. J.; Mayes, D. Α.; Russel, D. A . Photochem Photobiol. 1995, 62, 542. Cook, M. J. J. Mater. Sc.: Mat. Electr. 1994, 5, 117. Kobayashi, N; Nakajima, S.; Osa, T. Inorg. Chim. Acta 1993, 210, 131. Cherodian, A . N.; Davies, A . N.; Richardson , R. M.; Cook, M. J.; McKeown, Ν . B.; Thomson, A . J.; Feijoo, J.; Ungar, G.; Harrison, K . J. Mol. Cryst. Liq. Cryst. 1991, 196, 103. McKeown, Ν. B.; Chambrier, I.; Cook, M. J. J. Chem. Soc., Perkin Trans. 1990, 1169. Chambrier I.; Cook M. J.; Cracknell, S. J.; McMurdo, J. J. Mater. Chem. 1993, 3, 841. Swarts, J. C.; Langner, E. H . G.; Shago, R. F.; Davis, W. L . Polym. Prepr. 2004, 45(1), 452. Cook, M. J.; Cracknell, S. J.; Harrison, K. J. J. Mater. Chem. 1991, 1, 703. Linsky, J. P.; Paul, T. R.; Nohr, R. S.; Kenney, M. E . Inorg. Chem. 1980, 19, 3131. Chambrier, I.; Cook, M. J.; Helliwell, M.; Powell, A . K . J. Chem. Soc., Chem. Commun. 1992, 444.


Metal-Containg and Metallosupramilecular Polymers and Materials

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