Papers by Shivaraj Yellappa
β‐Functionalized Push–Pull <i>opp</i> ‐Dibenzoporphyrins as Sensitizers for Dye‐Sensitized Solar Cells
Chemistry-an Asian Journal, Sep 26, 2017
A novel class of β-functionalized push-pull zinc opp-dibenzoporphyrins were designed, synthesized... more A novel class of β-functionalized push-pull zinc opp-dibenzoporphyrins were designed, synthesized and utilized as sensitizers for dye-sensitized solar cells. Spectral, electrochemical and computational studies were systematically performed to evaluate their spectral coverage, redox behavior and electronic structures. These porphyrins displayed much broader spectral coverage and more facile oxidation upon extension of π-conjugation. Free-energy calculations and femtosecond transient absorption studies (charge injection rate in the range of 1011 s-1) suggest efficient charge injection from the excited singlet state of porphyrin to the conduction band of the TiO2. The PCE of YH3 bearing acrylic acid linkers (η = 5.9%) is close to that of the best ruthenium dye N719 (η = 7.4%) under similar conditions. The superior photovoltaic performance of YH3 is attributed to its higher light harvesting ability and its more favorable electron injection and collection as supported by electrochemical impedance spectral studies. This work demonstrates the exceptional potentials of benzoporphyrins as sensitizers for dye-sensitized solar cells.
(Invited) Push-Pull P-Extended porphyrins As Sensitizer for Dye-Sensitized Solar Cells
Meeting abstracts, 2017
Significant progress has been made on dye-sensitized solar cells sensitized by push-pull porphyri... more Significant progress has been made on dye-sensitized solar cells sensitized by push-pull porphyrins in recent years.1-3 Through installing push-pull groups at porphyrin meso-positions, exceptionally high power conversion efficiencies have been achieved.4, 5 In this presentation, we present the synthesis and characterization of a series of novel opp-dibenzoporphyrins, and their application as sensitizers for dye-sensitized solar cells. These porphyrin sensitizers are designed through installation of push (electron-donating) and pull (electron-withdrawing) groups at the porphyrin beta-positions. Significant push-pull effects were observed for these porphyrins. The effect of different conjugated spacers on the power conversion efficiency of these dyes was investigated. It was found that inclusion of ethynylphenyl bridge between the donating group and porphyrin core would segregate the frontier orbitals. Our data also show that conjugated bridges appear to play important roles in determining their power conversion efficiency. The electronic and optical properties of these pi-extended porphyrins were measured using UV-Vis spectroscopy, life-time and steady state fluorescence spectroscopy, and cyclic voltammetry. DFT calculations were also performed for these porphyrins. Reference 1. T. Higashino and H. Imahori, Dalton Trans., 2015, 44, 448-463. 2. M. Urbani, M. Gratzel, M. K. Nazeeruddin and T. Torres, Chem. Rev., 2014, 114, 12330-12396. 3. L. L. Li and E. W. Diau, Chem. Soc. Rev., 2013, 42, 291-304. 4. A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin, E. W.-G. Diau, C.-Y. Yeh, S. M. Zakeeruddin and M. Grätzel, Science, 2011, 334, 629-634. 5. S. Mathew, A. Yella, P. Gao, R. Humphry-Baker, B. F. Curchod, N. Ashari-Astani, I. Tavernelli, U. Rothlisberger, M. K. Nazeeruddin and M. Gratzel, Nat. Chem., 2014, 6, 242-247. Figure 1
The Chalkboard - Carbon Nanotubes: Next Generation of Electronic Materials
The Electrochemical Society interface, Jun 1, 2006
The current interest in carbon nanotubes is a direct consequence of the synthesis of buckminsterf... more The current interest in carbon nanotubes is a direct consequence of the synthesis of buckminsterfullerene, C60, in 1985 and its derivatives thereafter. The discovery that carbon could form stable, ordered structures other than graphite and diamond simulated many researchers in the world to search for other allotropes of carbon.
Collection of Czechoslovak Chemical Communications, Jun 1, 2017
Phenothiazine sensitized solar cells: Effect of number of cyanocinnamic acid anchoring groups on ... more Phenothiazine sensitized solar cells: Effect of number of cyanocinnamic acid anchoring groups on DSSC performance Shivaraj Yellappa, [a,b] Whitney A. Webre, [a] Habtom B. Gobeze, [a] Anna Middleton, [a] Chandra B. KC, [a] and Francis D'Souza *[a] Dye-sensitized solar cells (DSSCs) were built to probe the effect of number of cyanocinnamic acid anchoring groups on the ring periphery of phenothiazine dyes. Two kinds of dyes, one having substitution on the N-terminal (1) and the other at the C-3 aromatic ring (2-5) have been synthesized for this purpose. Additionally the number of cyanocinnamic acid groups have been increased to two in the case of compound 6. The N-terminal in the case of compounds 2-6 was functionalized to carry either a methyl, 2-hydroxyethane, tris(ethylene oxide) and hexyl group. Evidence for charge injection from the excited singlet state of phenothiazine to TiO2 was secured from femtosecond transient absorption spectral studies wherein ultrafast charge injection process (kCI ~ 10 10-10 11 s-1) was witnessed. The DSSCs were built on nanocrystalline TiO2 using the traditional two-electrode method. Cell performance was found to be better for Cfunctionalized phenothiazine dyes compared to N-functionalized ones, and having the second cyanocinnamic group increased the efficiency to 5.8 %.
The Chalkboard - Carbon Nanotubes: Next Generation of Electronic Materials
The Electrochemical Society Interface, 2006
The current interest in carbon nanotubes is a direct consequence of the synthesis of buckminsterf... more The current interest in carbon nanotubes is a direct consequence of the synthesis of buckminsterfullerene, C60, in 1985 and its derivatives thereafter. The discovery that carbon could form stable, ordered structures other than graphite and diamond simulated many researchers in the world to search for other allotropes of carbon.
ChemPlusChem, 2017
Dye‐sensitized solar cells (DSSCs) were built to probe the effect of the number of cyanocinnamic ... more Dye‐sensitized solar cells (DSSCs) were built to probe the effect of the number of cyanocinnamic acid anchoring groups on the ring periphery of phenothiazine dyes. Two kinds of dyes, one with substitution on the N‐terminal (1) and the other at the C‐3 aromatic ring (2–5), have been synthesized for this purpose. Additionally, the number of cyanocinnamic acid groups have been increased to two in the case of compound 6. In the case of compounds 2–6, the N terminus was functionalized to carry methyl, 2‐hydroxyethane, tris(ethylene oxide), or hexyl groups. Evidence for charge injection from the excited singlet state of phenothiazine to TiO2 was secured from femtosecond transient absorption spectral studies, wherein an ultrafast charge injection process (kCI≈1010–1011 s−1) was witnessed. The DSSCs were built on nanocrystalline TiO2 by using the traditional two‐electrode method. Cell performance was better for carbon‐functionalized phenothiazine dyes compared with that of nitrogen‐function...
Chemistry, an Asian journal, Jan 11, 2017
A novel class of β-functionalized push-pull zinc opp-dibenzoporphyrins were designed, synthesized... more A novel class of β-functionalized push-pull zinc opp-dibenzoporphyrins were designed, synthesized and utilized as sensitizers for dye-sensitized solar cells. Spectral, electrochemical and computational studies were systematically performed to evaluate their spectral coverage, redox behavior and electronic structures. These porphyrins displayed much broader spectral coverage and more facile oxidation upon extension of π-conjugation. Free-energy calculations and femtosecond transient absorption studies (charge injection rate in the range of 1011 s-1) suggest efficient charge injection from the excited singlet state of porphyrin to the conduction band of the TiO2. The PCE of YH3 bearing acrylic acid linkers (η = 5.9%) is close to that of the best ruthenium dye N719 (η = 7.4%) under similar conditions. The superior photovoltaic performance of YH3 is attributed to its higher light harvesting ability and its more favorable electron injection and collection as supported by electrochemical ...
Bioconjugate Chemistry, 2006
The binding of nucleic acids by water soluble cobalt(II) tetrakis-N-methylpyridyl porphyrin, (TMP... more The binding of nucleic acids by water soluble cobalt(II) tetrakis-N-methylpyridyl porphyrin, (TMPyP)Co and its highly electron deficient derivative, cobalt(II) tetrakis-N-methyl pyridyl-βoctabromoporphyrin, (Br 8 TMPyP)Co was investigated by UV-visible absorption, circular dichroism (CD), electrochemical and gel electrophoresis methods. The changes of the absorption spectra during the titration of these complexes with polynucleotides revealed a shift in the absorption maxima and a hypochromicity of the porphyrin Soret bands. The intrinsic binding constants were found to be in the range of 10 5-10 6 M −1. These values were higher for more electron deficient (Br 8 TMPyP)Co. Induced CD bands were noticed in the Soret region of the complexes due to the interaction of these complexes with different polynucleotides and an analysis of the CD spectra supported mainly external mode of binding. Electrochemical studies revealed the cleavage of polynucleotide by (TMPyP)Co and (Br 8 TMPyP)Co in the presence of oxygen preferentially at the AT base pair region. Gel electrophoresis experiments further supported the cleavage of nucleic acids. The results indicate that the β-pyrrole brominated porphyrin, (Br 8 TMPyP)Co binds strongly and cleaves nucleic acids efficiently as compared to (TMPyP)Co. This electrolytic procedure offers a unique tool in biotechnology for cleaving double-stranded DNA with specificity at the AT regions.
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Papers by Shivaraj Yellappa