Novel Lipophilic Lanthanide Bis-Phthalocyanines Functionalized by Pentadecylphenoxy Groups: Synthesis, Characterization and UV-Photostability

Maria Hofer,Roberta Del Sole,Ermelinda Bloise,Rudolf Słota,Giuseppe Mele,Gabriela Dyrda

doi:10.3390/molecules170910738

Maria Hofer, Roberta Del Sole + Show 4 more

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https://doi.org/10.3390/molecules170910738

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Journal: Molecules	Publication Date: Sep 7, 2012
Citations: 38	License type: CC BY 4.0

Affiliation: Opole University, University of Salento

Abstract

Novel sandwich-type phthalocyanines containing a rare earth metal core (Pr, Nd, Eu–Lu) and macrocycles peripherally substituted by pentadecylphenoxy groups were synthesized using a cardanol-based phthalonitrile precursor and the respective lanthanide acetate. Additionally, the metal free-base analog compound was studied for comparison. The purified reaction products were all found to be thick and viscous substances at room temperature, showing liquid crystalline behavior with a distinct increase in fluidity at ca. 40 °C. The complexes are readily soluble in chloroalkyl solvents and dissolve fairly well in DMF with some tendency to form aggregates. Besides they are strongly hydrophobic and reveal a peculiar affinity for lipophilic media. The compounds have been characterized by UV-Vis (absorption and emission), FTIR, MS and DSC methods. Photochemical activity in the liquid phase (dimethylformamide, dichloromethane, mineral oil) and the degree of photodegradation demonstrated under constant UV-irradiation (λ = 352 nm) have been analyzed and discussed in terms of photostability.

Highlights

The first successful synthesis of lanthanide phthalocyanine double-deckers reasonably documented by spectral data was simultaneously reported by the two independent Russian research groups of Plyushev and Kirin in the 1960s [1,2]
The rare earth phthalocyanine derivatives have been placed among the highest ranked molecular materials considered important for hi-tech applications [3]
The compounds explored in this study revealed diverse resistance to the UV radiation, the metal free base phthalocyanine proved definitely unstable in dichloromethane solution (H2Pc-R4 is insoluble in DMF)

Summary

Introduction

The first successful synthesis of lanthanide phthalocyanine double-deckers reasonably documented by spectral data was simultaneously reported by the two independent Russian research groups of Plyushev and Kirin in the 1960s [1,2] Soon after, it was found these peculiar complexes possessed very interesting electronic and optoelectronic properties, unique among the phthalocyanine family. Two macrocycles coordinated by the rare earth metal template (Ln) create a very stable π-electronic bonding system (Figure 1) which is considered a neutral sandwich radical having the electronic charge delocalized over both the Pc units [5] Such an arrangement allows for changing the distribution of electronic density within the cores of the particular phthalocyanine moieties whereas the molecular structure of the sandwich complex remains intact. This fact is believed to reflect some kind of specific flexibility of the electronic clouds of the Pc rings in LnPc2, manifested as a result of internal and/or external polarization effects [5,7,8]

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Results

Conclusion