Influence of electron-withdrawing and electron-donating substituents on photophysical properties of azaphthalocyanines
New zinc azaphthalocyanines (AzaPc) were prepared using a statistical method of synthesis starting from 5,6-bis(tert-butylsulfanyl)pyrazine-2,3-dicarbonitrile (A) and 2,3-dicyano-5,6-dibutoxycarbonylpyrazine (B). All the six possible AzaPc derivatives were detected on TLC and isolated using column chromatography on silica, however, the adjacent (AABB) and opposite (ABAB) isomers were not separated. Singlet oxygen quantum yields (ΦΔ) were measured using the DPBF decomposition method. It was found that presence of carbonyl group bounded directly to the macrocyclic core of AzaPc slightly decreases their ΦΔ in dependence on the number of the butoxycarbonyl groups in succession 0.67, 0.68, 0.67, 0.59, 0.51 for AAAA, AAAB, ABAB (AABB), ABBB and BBBB type of AzaPc, respectively. Similar dependences were found in the case of fluorescence quantum yield. Conjugation of COOR group with π-macrocyclic system leads to a somewhat bigger red-shift of the Q-band when compared with the red-shift caused by participation of lone pair of sulfur in π-system. In contrast, the former substituents cause less hyperchromic shift at all λmax then the tert-butylsulfanyl substituents.
Journal: Journal of Photochemistry and Photobiology A: Chemistry - Volume 186, Issues 2–3, 25 February 2007, Pages 316–322