Ring-Expanded Phthalocyanines Fused with Fluorene Skeleton for Light-Harvesting in the Near-IR Region
Phthalocyanines (Pcs) and their metal complexes (MPcs), synthetic porphyrin analogues, have been widely investigated as near-IR absorbing dyes because of their intense Q band (600-700 nm), high molar extinction coefficients (e > 100000 M-1 cm-1), and excellent thermal, chemical, and photolytic stabilities. The electronic structure and properties of MPcs can be tailored by modifying the macrocyclic ligands and changing the central metals .
We present here designed and synthesized novel ring-expanded zinc phthalocyanine (ZnFc , Figure1), in which four fluorene rings were fused with porphyrazine ring. Fusing fluorene rings with the porphyrazine rings lead to red-shifting the Q band and tailoring of the HOMO and LUMO energy levels as well as an expansion of p-system. We demonstrated the expansion of the light-harvesting area in BHJ solar cells based on poly(3-hexylthiophen) (P3HT) and 1-(3-methoxycalbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) by co-sensitizing with ZnFc. When the ZnFc decorated with eight alkyl chains was added to P3HT/PCBM BHJ solar cells, the solar cells showed a higher device efficiency with 16 % enhancement of JSC as compared with that of the reference P3HT/PCBM BHJ solar cells due to the expansion of light-harvesting range .
We also synthesized an asymmetrical fluorene-fused phthalocyanine (FcS1, Figure1), which containing three fused fluorene rings and one carboxylic acid. FcS1 indicated a potential for near-IR sensitizer in DSSCs. The absorption spectrum of FcS1 adsorbed onto a nano-crystalline TiO2 film suggested the formation of J-aggregation with tilted orientation of macrocyclic ligands. While the DSSC cells sensitized by FcS1 showed a modest efficiency of 3.2 % under simulated air mass 1.5 global sunlight, FcS1 could convert the red and near-IR light regions between 600 and 860 nm .
 J. Mack, N. Kobayashi, Chem. Rev. 2011, 111, 281-321.
 S. Yamamoto, M. Kimura, ACS Appl. Mater. Interfaces 2013, 5, 4367-4373.