Elsevier

Journal of Luminescence

Volume 180, December 2016, Pages 219-223
Journal of Luminescence

Full Length Article
First investigation on the photophysical and photochemical properties of azo-bridged phthalocyanine photosensitizers

https://doi.org/10.1016/j.jlumin.2016.08.039Get rights and content

Abstract

Novel azo-bridged indium(III) acetate phthalocyanine was synthesized by cyclotetramerization reaction of (E)-4-((2,5-dimethoxyphenyl)diazenyl)phthalonitrile. This phthalocyanine was fully characterized by FT-IR, 1H-NMR, UV–vis and MALDI-TOF mass spectroscopic techniques and elemental analyses as well. Additionally, the photophysical and photochemical properties of this phthalocyanine was investigated for the first time. The obtained results were compared with azo-bridged zinc(II) and metal-free phthalocyanine counterparts for determination of central metal effect on these properties. These results were also compared with unsubstituted zinc(II) and indium(III)acetate phthalocyanines for determination of substitution effect on the photophysical and photochemical properties.

Introduction

The primary objective in cancer treatment is the selective destruction of tumor cells without damage to normal cells and tissues. Photodynamic therapy (PDT) is a rising cancer treatment that takes advantage of the interaction between light and a photosensitizing agent to produce reactive oxygen in tumor cells [1]. When localized in the target tissue, the photosensitizer is activated by light to produce oxygen intermediates that destroy target tissue cells. The phthalocyanines (Pcs) are the most used compounds as photosensitizers (PSs) in PDT since they have suitable photophysical and photochemical properties such as strong absorbance at long wavelengths and chemical tunability through addition of substituents on the periphery of the macrocycle or on the axial position for certain central metals [2], [3], [4]. Pcs exhibit strong absorptions in both UV and visible region of the electronic spectra as expected from the extensively conjugated aromatic chromophore due to their intense π–π* transitions [5]. The Pcs have an extended conjugated network of π electrons when they are modified by azo-bridged substitution and their π–π* transition energies change due to extension of the conjugation. Thus, they may become more suitable PSs for PDT.

In the last decade, beside their applications in PDT of cancer [6], Pcs are largely used as active materials in various technological areas such as gas and chemical sensors [7], [8], molecular solar cells [9], industrial catalytic systems [10], [11], electrochromic display devices [12], information storage systems [13], optical switching [14], liquid crystals [15], nanotechnology [16], [17], [18] and light-emitting devices [19].

For a specific high-technological application, the lower solubility of the unsubstituted metallo- and metal free Pcs can be present some problems, but the peripheral substituents and their bridge types on Pc skeleton make a strong influence on the π-electron conjugation of the macromolecule thus it makes solvation easier [20]. The substituents can also be used as anchoring or bridging groups for the formation of controlled supramolecular assemblies or different applications (e.g. heterogeneous catalysis) [21].

In our previous study, the starting material (E)-4-((2,5-dimethoxyphenyl)diazenyl)phthalonitrile. (1) was synthesized by the reaction of 4-aminophthalonitrile with 1,4-dimethoxybenzene. Then metal-free and zinc(II) Pcs were synthesized and their toluene vapor sensing properties were investigated [21]. One of the most striking features in the present study was the synthesis of π-extended azo-bridged Pcs, to be used to obtain information about the structural factors governing the investigation of their photophysical and photochemical properties, and also about the effects of extra conjugation of the π-system on the absorption wavelength of the molecule (near infrared absorbers). Thus, the photophysical and photochemical properties of the earlier synthesized azo-bridged zinc(II) (2) and metal-free (4) Pcs [21] and the novel indium(III)acetate Pc derivative were investigated for determination of the influence of the variety of the central metal ions in Pc cavity on these properties. The photophysical and photochemical properties of these Pcs were studied in dimethylsulfoxide (DMSO) solutions because the small amount of DMSO can be used for biological applications without any toxic effect [22], [23], [24], [25], [26]. Also, the obtained results were compared with the unsubstituted ZnPc and In(OAc)Pc for the first time in this study for determination of substituent effect on these properties.

Section snippets

Materials and methods

The used materials, equipments, photophysical and photochemical formulas and parameters were supplied in the Supplementary information.

(E)-2(3),9(10),16(17),23(24)-Tetrakis-[(2,5-dimethoxyphenyl)diazenyl] phthalocyaninato indium(III)acetate (3)

Compound 1 (0.23 g, 0.76 mmol) and In(OAc)3 (0.13 g, 0.45 mmol) was powdered in a quartz crucible and transferred in a reaction tube. 0.25 mL of DMF and 0.25 mL 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) which is a catalyst were added to this reaction mixture, and then the mixture was heated at 360 °C in the sealed glass tube for 20 min under dry nitrogen atmosphere.

Synthesis and characterization

Phthalonitrile 1, zinc(II)Pc 2 and metal-free Pc 4 were synthesized, purified and characterized according to the procedures given in the literature [21]. The novel In(OAc)Pc 3 was synthesized by the reaction of phthalonitrile 1 with In(OAc)3 in DMF in the present of DBU as a base (Scheme 1) and it was characterized by FT-IR, UV–vis, 1H-NMR and MALDI-TOF mass spectroscopic data and elemental analysis values. The obtained data were confirmed the proposed structure of novel In(OAc)Pc.

The infrared

Conclusions

The novel peripherally In(OAc)Pc (3) containing azo-bridged 2,5-dimethoxyphenoxy groups was synthesized for the first time. This phthalocyanine was characterized by elemental analysis and different spectroscopic techniques such as UV–vis, FT-IR, 1H-NMR and MALDI-TOF mass. The effects of the nature of metal atom in the Pc cavity and 2,5-dimethoxyphenyl group as substituent on Pc skeleton on spectroscopic, aggregation, photophysical and photochemical properties were investigated in DMSO. All

Acknowledgments

We are thankful to Marmara University, The Commission of Scientific Research Projects (BAPKO) (Project No: FEN-C-YLP-111115-0515).

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