Azaphthalocyanines with extended conjugation through heteroaryl and aryl substituents: Photochemical and photophysical properties

Abstract

Magnesium and zinc complexes of azaphthalocyanines (AzaPc) with eight peripheral aromatic (phenyl) or heteroaromatic (pyridyl, thienyl, furyl) substituents are studied from the point of view of their singlet oxygen (Φ Δ ) and fluorescence (Φ F ) quantum yields, and UV-vis absorption spectra. Zn complexes have higher Φ ∆ than Mg complexes by a factor of two, whereas the Mg complexes have higher Φ F than Zn complexes, also by a factor of two. Thienyl AzaPc have the highest Φ ∆ among all studied substances (0.635 for Zn complex) followed by phenyl and pyridyl derivatives. The order of Φ F values is then reversed -the highest values were reached for pyridyl and phenyl derivatives followed by thienyl AzaPc. Both furyl AzaPc were unstable towards light and decomposed giving very low Φ ∆ and Φ F . The Q-bands of the furyl and thienyl AzaPc were red-shifted for approx. 20 nm compared to phenyl and pyridyl derivatives indicating lower sterical hindrance between five-membered rings and thus allowing better conjugation of π-systems. Pyridyl-, thienyl-and furylsubstituted pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles were also prepared but decomposed during attempted cyclotetramerizations.

Tetra(pyrazino[2,3-b]pyrazino)porphyrazines: Synthesis, absorption, photophysical and electrochemical properties of strongly electron-deficient macrocycles

“…Thus, alkylsulfanyl 6a (l max = 705 nm) and dialkylamino 6c (l max = 693 nm) were considerably red shifted when compared to the aryloxy TPyzPyzPz 6b (l max = 682 nm) similarly as reported for analogous TPyzPzs [15]. Even larger extension of the conjugated system can be achieved for hetaryl substituted derivatives 6d (l max = 720 nm) and 6f (l max = 739 nm), again in line with previous observations made for TPyzPzs [8]. Comparison can be made also with their analogous compounds with different rings fused to the porphyrazine core.…”

“…Direct condensation of 1 with vicinal dihetaryl substituted diketones gave dihetaryl substituted 4d-4f as reported in literature [8]. However, all attempts to synthesize dialkyl substituted 4g and 4h failed and only starting materials were detected on TLC even after several days of reflux of 1 with corresponding aliphatic vicinal diketones in acetic acid.…”

“…In this case, the reduction occurs more likely on the pyrazine ring with methoxy groups as suggested by the good match of measured and predicted 13 C NMR spectra. Previously, we have reported unsuccessful cyclotetramerization of 4d-4f employing various methods (lithium butoxide, magnesium butoxide or zinc acetate in quinoline) [8]. In our present work, the syntheses were performed again with 4a-4f and mainly decomposition products were obtained for 4c-4f.…”

“…Gary et al reported that the Linstead type cyclotetramerization of 6,7-diphenylpyrazino[2,3-b]pyrazine-2,3-dicarbonitrile resulted only in substitution of its nitrile groups by an available nucleophile such as an alcohol to give aromatic ethers [1]. Mørkved et al reported only decomposition of starting mono-or dihetaryl substituted pyrazino [2,3-b]pyrazine-2,3-dicarbonitriles under both Linstead type or template supported methods [7,8]. For this reason, only two papers in peer-reviewed journals [9,10] and one patent [11] can be found to have reported on successful TPyzPyzPzs synthesis.…”

Synthesis and properties of azaphthalocyanines with 1,2,3,4-tetrahydropyrazino[2,3-b]pyrazine moiety

“…[1,2] Their large π-conjugated macrocyclic system is responsible for interesting optical, [3] photochemical, photophysical [4] or redox properties. [5] For this reason they have been systematically investigated as promising compounds in many areas including photodynamic therapy (PDT), [6,7] non-linear optics, [8,9] photovoltaics [10] and electrochemistry.…”