title: Low-Symmetry Ω-Shaped Zinc Phthalocyanine Sensitizers with Panchromatic Light-Harvesting Properties for Dye-Sensitized Solar Cells.
abstract: Two low-symmetry phthalocyanines (Pcs) substituted with thiophene units at the non-peripheral (α) and peripheral (β) positions were synthesized and their optical, electronic-structure, and electrochemical properties were investigated. The substitution of thiophene units at the α positions of the phthalocyanine skeleton resulted in a red shift of the Q band and significantly modified the molecular-orbital electronic distributions just below the HOMO and just above the LUMO, with distortion of the typical Gouterman four-orbital arrangement of MOs. Two amphiphilic Ω-shaped ZnPcs (αPcS1 and αPcS2) bearing a π-conjugated side chain with an adsorption site at an α position of the Pc macrocycle were synthesized as sensitizers for dye-sensitized solar cells (DSSCs). The absorption spectra of αPcS1 and αPcS2 showed red shifted Q bands and a broad band from 350 to 550 nm assignable to the intramolecular charge-transfer transition from the ZnPc core to the side chains. Time-dependent DFT calculations provided a clear interpretation of the effect of the thiophene conjugation on the typical phthalocyanine core π MOs. Compound αPcS1 was used as a light-harvesting dye on a TiO2electrode for a DSSC, which showed a panchromatic response in the range 400-800 nm with a power conversion efficiency of 5.5 % under one-sun conditions.
authors.affiliation: Division of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Ueda, 386-8567, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamamoto
authors.affiliation: Department of Chemistry and Department of Biology, The University of Western Ontario, London, Ontario, N6A 5B7, Canada.
authors.forename: Angel
authors.initials: A
authors.lastname: Zhang
authors.affiliation: Department of Chemistry and Department of Biology, The University of Western Ontario, London, Ontario, N6A 5B7, Canada.
authors.forename: Martin J
authors.identifier: http://orcid.org/0000-0001-6799-7560
authors.initials: MJ
authors.lastname: Stillman
authors.affiliation: Division of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Ueda, 386-8567, Japan.
authors.forename: Nagao
authors.initials: N
authors.lastname: Kobayashi
authors.affiliation: Division of Chemistry and Materials, Faculty of Textile Science and Technology, Shinshu University, Ueda, 386-8567, Japan.
authors.forename: Mutsumi
authors.identifier: http://orcid.org/0000-0003-3050-8254
authors.initials: M
authors.lastname: Kimura
keywords: density functional calculations; dyes/pigments; phthalocyanines; sensitizers; solar cells