Azaphtalocyanines with extended conjugation through heteroaryl and aryl substituents. Photochemical and photophysical properties

Summary

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 (ΦΔ) and fluorescence (ΦF) quantum yields, and UV-vis absorption spectra. Zn complexes have higher ΦΔ than Mg complexes by a factor of two, whereas the Mg complexes have higher ΦF than Zn complexes, also by a factor of two. Thienyl AzaPc have the highest ΦΔ among all studied substances (0.635 for Zn complex) followed by phenyl and pyridyl derivatives. The order of ΦF 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 ΦΔ and ΦF 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 pi-systems. Pyridyl-, thienyl- and furyl-substituted pyrazino[2,3-b]pyrazine-2,3-dicarbonitriles were also prepared but decomposed during attempted cyclotetramerizations.