Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 6. Chemical and Redox Properties and Highly Effective Photosensitizing Activity for Singlet Oxygen Production of Penta- and Monopalladated Complexes in Dimethylformamide Solution

Abstract

Tetrakis-2,3-[5,6-di-(2-pyridyl)pyrazino]porphyrazinatopalladium(II) [Py 8TPyzPzPd] ( 1) and the corresponding pentapalladated species [(PdCl 2) 4Py 8TPyzPzPd] ( 2), dissolved (c approximately 10 (-5)-10 (-6) M) in preacidified dimethylformamide ([HCl] approximately 10 (-4) M), behave as potent photosensitizing agents for the production of singlet oxygen, (1)O 2, with Phi Delta values of 0.89 +/- 0.04 and 0.78 +/- 0.05, respectively. The related octacation [(2-Mepy) 8TPyzPzPd] (8+) ( 3), examined under similar experimental conditions, exhibits lower Phi Delta values, that is, 0.29 +/- 0.02 (as an iodide salt) and 0.32 +/- 0.02 (as a chloride salt). In view of the very high values of Phi Delta, the photophysics of complexes 1 and 2 has been studied by means of pump and probe experiments using ns laser pulses at 532 nm as excitation source. Both complexes behave like reverse saturable absorbers at 440 nm because of triplet excited-state absorption. The lifetimes of the triplet excited states are 65 and 96 ns for the penta- and mononuclear species, respectively. Fluorescence quantum yields (Phi f) are approximately 0.1% for both 1 and 2. Such low Phi f values for the two complexes are consistent with the high efficiency of triplet excited-state formation and the measured high yields of (1)O 2. Time-dependent density-functional theory (TDDFT) calculations of the lowest singlet and triplet excited states of the mono- and pentapalladated species help to rationalize the photophysical behavior and the relevant activity of the complexes as photosensitizers for the (1)O 2 ( (1)Delta g) generation.

Tetrapyrazinoporphyrazines and their metal derivatives. Part I: Synthesis and basic structural information

“…Variably from batch to batch for each single species the number of clathrated water molecules can reach 15-20 for macrocyclic unit. The UV-vis and fluorescence spectral response of the most of the macrocycles and their potentialities as photosensitizers for the generation of singlet oxygen ( 1 O 2 ), of interest in photodynamic therapy [53,56,58,59,209,210,213], and as bi-multimodal anticancer drugs [57,59] were also studied. The metal free macrocycle [TPyz42PzH 2 ] (A in Scheme 31) was obtained by direct cyclotetramerization of the dinitrile precursor Pyz42, in the presence of DBU [119].…”

“…Peripheral substituents endow TPyzPzs not only with solubility in organic or aqueous solvents, but also fine-tune spectral and other physico-chemical properties and biological activity. In the recent decade, these new peripherally substituted macrocycles have been especially studied as promising species for application in photodynamic therapy (PDT) [49][50][51][52][53][54][55] and plurimodal cancer therapy [56][57][58][59] and as active catalysts in redox processes [60][61][62][63][64][65]. In the following sections, different types of pyrazine-annulated porphyrazines and their metal derivatives will be considered with an emphasis primarily on the synthetic and structural aspects.…”

Zinc azaphthalocyanines with thiophen-2-yl, 5-methylthiophen-2-yl and pyridin-3-yl peripheral substituents: Additive substituent contributions to singlet oxygen production

“…Pyrazine-2,3-dicarbonitrile 7 2.2.6.1. 5-(5-Methylthiophen-2-yl)-6-(pyridin-3-yl)pyrazine-2,3-dicarbonitrile (7). A solution of 6 (1.3 mmol, 0.3 g) and DAMN (3 mmol, 0.3 g) in glacial acetic acid (10 ml) was heated under reflux for 2.5 h. The solvent was removed under reduced pressure, and the solid residue was chromatographed on silica with acetone.…”

“…AzaPcs are closely related to phthalocyanines (Pc) as well; some of the benzene carbon atoms of the Pc macrocycle have been replaced by nitrogen atoms [5]. Generally, this interesting class of dyes has found use in several applications, due to non-linear optical behaviour [6], metal binding [7] or catalytic properties [8].…”

Conjugated macrocyclic materials with photoactivated optical absorption for the control of energy transmission delivered by pulsed radiations

“…In plot at the given distance L = 1 mm when λ = 532 nm and pulse duration is 7 ns. Plot (b) reports the transmitted energy as a function of L when I 0 The analogs of Pcs that have been considered for OL purposes are of various nature (Chart 9), and porphyrazines (52) [61], ], cyclo-[8]-pyrrole (53)] among others[45]. Structures of the OL active complexes 51-58 with conjugated macrocycles as ligands.…”