Carbazole‐Fused Zinc(II)−Phthalocyanine Sensitizers

Ring‐expanded zinc phthalocyanines 3, 4, and PcS27 were synthesized from new carbazole‐fused phthalonitriles 1 and 2, and the effect of direct annulation of heterocycles with the phthalocyanine macrocycles on their optical and electrochemical properties were investigated. Carbazole‐fused zinc phthalocyanine 3 exhibited an intense Q band in the near‐infrared‐light region, owing to destabilization of the HOMO energy level, whilst low‐symmetry push–pull compound 4 showed a well‐defined split Q band, owing to splitting of the LUMO and LUMO+1 energy levels. Sensitizer PcS27, which had a donor–π‐linker–acceptor structure, showed a panchromatic response from the visible‐light region to the near‐infrared‐light region if used as a light‐harvesting dye on TiO2 electrodes for dye‐sensitized solar cells.