title: The origin of the unusual broad and intense visible absorption of tetrathiafulvalene-annulated zinc porphyrazine: a density functional theory study.
abstract: The vertical excitation energies of tetrathiafulvalene (TTF)-annulated zinc porphyrazine (ZnPzTTF) were investigated using time-dependent density functional theory (TDDFT) calculations and compared to the experimental UV-vis spectra. To examine the effects of the aza substitutions and TTF groups on the molecular properties, zinc complexes of porphyrin (ZnP), porphyrazine (ZnPz) and tetraTTF-annulated porphyrin (ZnPTTF) were also selected for comparison. It was shown that numerous electronic transitions with TTF-to-porphyrin or porphyrazine charge transfer character exist and the Q band of ZnPzTTF is dominated by TTF-to-porphyrazine charge transfer transition mixed with porphyrazine core unit itself except for classic porphyrazine π→π* transitions. The Q band of ZnPzTTF mixes with other configurations, which breaks down the Gouterman's classic four-orbital model for the spectral interpretation. The data suggest that TDDFT/SAOP performs best for Q and B bands of ZnPzTTF with the maximum error in excitation energy being 0.17 eV. The CAM-B3LYP, ωB97XD and M06-2X calculations qualitatively predict that the low-lying electronic transitions of ZnPzTTF with TTF-to-porphyrazine charge transfer character located below the Q band. The broad and intense red-shifted Q band suggests that ZnPzTTF can be a candidate for dye-sensitized solar cells.
authors.affiliation: Institute of Functional Material Chemistry, Faculty of Chemistry, Northeast Normal University, Changchun, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Tao
authors.forename: Yu-He
authors.initials: YH
authors.lastname: Kan
authors.forename: Shui-Xing
authors.initials: SX
authors.lastname: Wu
authors.forename: Hai-Bin
authors.initials: HB
authors.lastname: Li
authors.forename: Li-Kai
authors.initials: LK
authors.lastname: Yan
authors.forename: Shi-Ling
authors.initials: SL
authors.lastname: Sun
authors.forename: Zhong-Min
authors.initials: ZM
authors.lastname: Su
mesh_terms: D006571:Heterocyclic Compounds / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry*; D008958:Models, Molecular; D011166:Porphyrins / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry*
chemical_list: D006571:Heterocyclic Compounds; D008665:Metalloporphyrins; D011166:Porphyrins; C063887:tetrathiafulvalene; D015032:Zinc