title: Sensitive efficiency of photoinduced electron transfer to band gaps of semiconductive single-walled carbon nanotubes with supramolecularly attached zinc porphyrin bearing pyrene glues.
abstract: Photoinduced electron transfer in self-assembled single-walled carbon nanotube (SWNT)/zinc porphyrin (ZnP) hybrids utilizing (7,6)- and (6,5)-enriched SWNTs has been investigated. Toward this, first, zinc porphyrin was covalently functionalized to possess four pyrene entities (ZnP(pyr)(4)). Exfoliation of the semiconducting nanotube bundles occurred due to pi-pi-type interactions with the pyrene and porphyrin entities in organic solvents. The nanohybrids thus formed were isolated and characterized by TEM, UV-visible-near-IR, and Raman spectroscopy. Free-energy calculations suggested the possibility of electron transfer in both the (7,6)- and (6,5)-possessing ZnP(pyr)(4)/SWNT nanohybrids. Accordingly, fluorescence studies revealed efficient quenching of the singlet excited state of ZnP in the nanohybrids, originating from the charge separation, as confirmed by observation of a ZnP pi-cation radical in transient absorption spectra. The rates of charge separation were found to be slightly higher for (7,6)-SWNT-derived hybrids compared to the (6,5)-SWNT-derived hybrids. Charge recombination revealed an opposite effect, indicating that the (7,6)-SWNTs are slightly better for charge stabilization compared to the (6,5)-SWNTs. The present nanohybrids were further utilized to photochemically reduce the hexyl viologen dication in the presence of a sacrificial electron donor in an electron-pooling experiment, offering additional proof for the occurrence of photoinduced charge separation and potential utilization of these materials in light-energy-harvesting applications. Finally, solar cells constructed using the ZnP/SWNT hybrids revealed higher efficiency for the ZnP(pyr)(4)/(7,6)-SWNT hybrid with narrower nanotube band gap compared with the ZnP(pyr)(4)/(6,5)-SWNT having a relatively wider band gap.
authors.affiliation: Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, Kansas 67260-0051, USA.
authors.forename: Eranda
authors.initials: E
authors.lastname: Maligaspe
authors.forename: Atula S D
authors.initials: AS
authors.lastname: Sandanayaka
authors.forename: Taku
authors.initials: T
authors.lastname: Hasobe
authors.forename: Osamu
authors.initials: O
authors.lastname: Ito
authors.forename: Francis
authors.initials: F
authors.lastname: D'Souza