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Satsumasendai, Japan

Sandanayaka A.S.D.,Japan Advanced Institute of Science and Technology | Sandanayaka A.S.D.,Keio University | Subbaiyan N.K.,Wichita State University | Das S.K.,Wichita State University | And 6 more authors.

A non-covalent double-decker binding strategy is employed to construct functional supramolecular single-wall carbon nanotubes (SWCNT)-tetrapyrrole hybrids capable of undergoing photoinduced electron transfer and performing direct conversion of light into electricity. To accomplish this, two semiconducting SWCNTs of different diameters (6,5 and 7,6) were modified via π-π stacking of pyrene functionalized with an alkyl ammonium cation (PyrNH 3 +). Such modified nanotubes were subsequently assembled via dipole-cation binding of zinc porphyrin with one (1) or four benzo-18-crown-6 cavities (2) or phthalocyanine with four benzo-18-crown-6 cavities at the ring periphery (3), employed as visible-light photosensitizers. Upon charactering the conjugates using TEM and optical techniques, electron transfer via photoexcited zinc porphyrin and phthalocyanine was investigated using time-resolved emission and transient absorption techniques. Higher charge-separation efficiency is established for SWCNT(7,6) with a narrow band gap than the thin SWCNT(6,5) with a wide band gap. Photoelectrochemical studies using FTO/SnO 2 electrodes modified with these donor-acceptor conjugates unanimously demonstrated the ability of these conjugates to convert light energy into electricity. The photocurrent generation followed the trend observed for charge separation, that is, incident-photon-to-current efficiency (IPCE) of a maximum of 12% is achieved for photocells with FTO/SnO 2/SWCNT(7,6)/PyrNH 3 +:1. © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

D'Souza F.,University of North Texas | D'Souza F.,Wichita State University | Das S.K.,University of North Texas | Zandler M.E.,Wichita State University | And 2 more authors.
Journal of the American Chemical Society

Photoinduced electron transfer in self-assemblies of porphyrins ion-paired with ssDNA wrapped around single-wall carbon nanotubes (SWCNTs) has been reported. To accomplish the three-component hybrids, two kinds of diameter-sorted semiconducting SWCNT(n,m)s of different diameter ((n,m) = (6,5) and (7,6)) and free-base or zinc porphyrin bearing peripheral positive charges ((TMPyP +)M (tetrakis(4-N-methylpyridyl)porphyrin); M = Zn and H 2) serving as light-absorbing photoactive materials are utilized. The donor-acceptor hybrids are held by ion-pairing between the negatively charged phosphate groups of ssDNA on the surface of the SWCNT and the positively charged at the ring periphery porphyrin macrocycle. The newly assembled bionano donor-acceptor hybrids have been characterized by transmission electron microscopy (TEM) and spectroscopic methods. Photoinduced electron transfer from the excited singlet porphyrin to the SWCNTs directly and/or via ssDNA as an electron mediator has been established by performing systematic studies involving the steady-state and time-resolved emission as well as the transient absorption studies. Higher charge-separation efficiency has been successfully demonstrated by the selection of the appropriate semiconductive SWCNTs with the right band gap, in addition to the aid of ssDNA as the electron mediator. © 2011 American Chemical Society. Source

Das S.K.,University of North Texas | Sandanayaka A.S.D.,Japan Advanced Institute of Science and Technology | Subbaiyan N.K.,University of North Texas | Zandler M.E.,Wichita State University | And 3 more authors.
Chemistry - A European Journal

Covalent functionalization of diameter sorted SWCNTs with porphyrins (MP), and photochemistry to establish nanotube diameter-dependent charge separation efficiencies are reported. The MP-SWCNT(n,m) [M=2 H or Zn, and (n,m)=(7,6) or (6,5)] nanohybrids are characterized by a variety of spectroscopic, thermogravimetric, TEM imaging techniques, and also by DFT MO calculations. The thermogravimetric, Raman and fluorescence studies reveal the presence of a moderate number of porphyrins on the SWCNT surface. The MO results suggest charge separation (CS) via the excited state of MP. Time-resolved fluorescence studies reveal quenching of the singlet excited state of the MP with SWCNT(n,m), giving the rate constants of charge separation (kCS) in the range of (4-5)×109 s-1. Nanosecond transient absorption measurements confirm the charge-separated radical cation and the radical anion as [MP.+-SWCNT.-] with their characteristic absorption bands in the visible and near-IR regions. The charge separated states persist for about 70-100 ns thus giving an opportunity to utilize them to build photoelectrochemical cells, which allowed us to derive the structure-reactivity relationship between the nature of porphyrin and diameter of the employed nanotubes. Size matters! Diameter-dependent efficiencies of photoinduced electron transfer leading to charge stabilization, and photoelectrochemical response of solar cells is demonstrated in porphyrin covalently linked to (7,6)- and (6,5)-enriched single-wall carbon nanotube (SWCNT) donor-acceptor nanohybrids (see figure; MP=metalloporphyrin). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Urbani M.,University of Castilla - La Mancha | Pelado B.,University of Castilla - La Mancha | De La Cruz P.,University of Castilla - La Mancha | Yamanaka K.-I.,Toyota Central R&D Labs. | And 3 more authors.
Chemistry - A European Journal

Unsymmetric dumbbell molecules based on N-methylpyrrolidine[60]fullerene, oligothienylenevinylenes (nTV; n=2, 4), and N-methylpyrrolidine[70]fullerene, namely, C 60-nTV-C 70 were synthesized and their photophysical properties were studied. In nonpolar solvents, photoinduced energy-transfer process predominantly takes place from the singlet excited state of nTV to C 60 and C 70, as was confirmed by time-resolved emission and transient absorption spectroscopy. In polar solvent, charge-separation processes take place instead of energy transfer. The generated charge-separated radical-ion pairs decay to the neutral molecules by a fast charge-recombination process; for n=4, a rate constant of 2 × 10 7 s -1 and lifetime of 50 ns were evaluated. Lopsided dumbbells: Two unsymmetrical dumbbell molecules based on N- methylpyrrolidinefullerene and oligothienylenevinylenes (nTV; n=2, 4) have been synthesized. An 1H NMR spectroscopic study allowed the identification of four different isomers formed due to the presence of C 70. Photoinduced charge-separation processes in polar solvents gave charge-separated radical-ion pairs (see figure) with a lifetime of 50 ns for n=4. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Uetomo A.,Osaka City University | Kozaki M.,Osaka City University | Suzuki S.,Osaka City University | Yamanaka K.-I.,Toyota Central R&D Labs. | And 3 more authors.
Journal of the American Chemical Society

A light-harvesting antenna 1 comprising three varieties of porphyrins, each having a different number of ethynyl groups at its meso positions, was designed and synthesized. Antenna 1 exhibits intense absorption throughout the visible region up to 700 nm. Steady-state and time-resolved fluorescence studies showed that singlet-excited-state energy transfer occurs from the peripheral porphyrins to the central porphyrin with >90% efficiency and rate constants on the order of 10 10 s -1. © 2011 American Chemical Society. Source

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