DEPOSITION OF PHTHALOCYANINES AND PORPHIRINS DERIVATIVES

L. Leo, G. Mele, G. Rosso, G. Stasi, L. Valli, G. Vasapollo

Dipartimento di Scienza dei Materiali, Università. di Lecce,

Via Arnesano I, 73100 Lecce (Italy)

Abstract.

Porphyrin-C₆₀ has been prepared by 1,3 dipolar cycloaddition using N-Methyl-glicine and formylporphyrin with C_60. Cu-Phthalocyanine-C₆₀ has been synthesised by reaction of 1,2 dicyano-4-(2’, 4’ di-tert-amyl-phenoxy)benzene with 1,2 dicyano-4-(4’-N-methyl-2-fulleropyrrolidine) in presence of CuCl₂ and DBU. The transfer of the porphyrin-C₆₀ dyad onto solid substrates by the Langmuir-Blodgett (LB) method has been analysed.

Introduction

The role of porphyrins and phthalocyanines films in sensors application received an increasing interest in recent years and new synthetic methodologies can provide the opportunities to explore new class of compounds. In addition, fullerene and its derivatives have been extensively studied for the understanding of their unique physical and chemical properties and because of the potential application in material science^,. The actual challenge is the fabrication of thin films of porphyrins, phthalocyanine, or dyads (for example porphyrin-linked phthalocyanines, porphyrin-linked fullerene, phthalocyanines-linked fullerene…), which must be synthesised ad hoc, in order to explore the electrical properties of these materials. Although there are a number of reports on fullerene, porphyrins, and phthalocyanines films, there exists only a quite limited number of LB films of dyads of these compounds. So that we report here the synthesis of porphyrin-C₆₀ and phthalocyanines – C₆₀ dyads and the fabrication of LB films of the porphyrin-C₆₀ dyad in mixture with arachidic acid.

Results and discussion

The synthesis of porphyrin-C₆₀ 5 was carried out as shown in the Scheme 1. Pyrrole was converted to dipyrromethane 1 by treatment with benzaldehyde in the presence of trifluoroacetic acid in 55% yield. Acid-catalysed condensation of 1 with mono protected aromatic dialdehyde 2 gave porphyrin 3. The desired dyad 5 was prepared by cycloaddition method reacting 4 with an equimolar amount of fullerene (C₆₀) and N-Methylglycine, in refluxing toluene solution under nitrogen for 48 h (44% yield). In the reaction a small amount of a compound in which two C₆₀ units are covalently linked to the porphyrin was also obtained. The purification of 5 was carried out by column chromatography and the structure confirmed by NMR spectra. The synthesis of Cu-phthalocyanine-C₆₀9 was carried out as shown in Scheme 2.

Scheme 1

Scheme 2

1,2-dicyano-4-nitro benzene was converted to 6 or 7, by treatment with 4-hydroxybenzaldheyde or 2,4-di-tert-amylphenol, respectively, in DMSO in the presence of K₂CO₃ in 55% and 61% yield.
Reaction of 7 and 8 in presence of CuCl₂ and DBU gave a mixture of isomers from which the isomer 9 was isolated by column chromatography and the structure confirmed by NMR spectra.
Derivative 5 has been transferred onto solid substrates by the LB technique. In order to construct the films, a 1:5 molar mixture of compound 5 and arachidic acid, respectively, has been used in chloroform as spreading solvent. The Figure 1 illustrates the isotherm on the water surface of this mixture. The resulting limiting area per molecule for arachidic acid is 28 Ų/molecule, thus indicating that the floating film probably consist of an arachidic acid monolayer with the dyad molecules lying onto it, as already observed for similar mixtures. This floating film has been then transferred onto various substrates, thus constructing multilayers containing up to 100 layers.

Figure 1

Conclusions

The synthesis of two dyads porphyrin-C₆₀ and phthalocyanine-C₆₀ has been reported. Further studies concerning the chemical and physical characterisation of the isolated compounds are in progress. The dyad porphyrin-C₆₀ has been transferred onto various substrates, thus constructing multilayers containing up to 100 layers; similar studies on the dyad phthalocyanine-C₆₀ are also in progress.

Foot Notes and References