Papers by abhinandan makhal
In this article, we will review our investigation on the key ultrafast processes in the light har... more In this article, we will review our investigation on the key ultrafast processes in the light harvesting dynamics of Zinc Oxide (ZnO)-based nanomaterials. Firstly, we describe our studies on light harvesting of the complex of ZnO nanoparticles (NPs) with biological probe Oxazine 1 in the near–infrared region using time picosecond-resolved fluorescence decay studies. We have used ZnO NPs and Oxazine 1 as model donor and acceptor respectively to explore the efficacy of the Förster resonance energy transfer (FRET) in the nanoparticle-dye system. It has been shown that FRET from the states localized near the surface and those in the bulk of the ZnO NPs can be resolved by measuring the resonance efficiency for various wavelengths of the emission spectrum. It has been observed that the states located near the surface for the NPs (contributing to visible emission at 550 nm) can contribute to very high efficiency (>90%) FRET. The efficiency of light harvesting dynamics of the ZnO nanorod...
The Journal of Physical Chemistry C, 2010
In this contribution we have studied the dynamics of light harvesting of ZnO nanoparticles (NPs) ... more In this contribution we have studied the dynamics of light harvesting of ZnO nanoparticles (NPs) to a surface adsorbed sensitizing dye (SD) N719. By using the picosecond resolved Fo ¨rster resonance energy transfer (FRET) technique we have explored that the excited ZnO NPs resonantly transfer visible optical radiation to the SD N719. The consequence of the energy transfer on the performance of the overall efficiency of a model ZnO NP-based dye-sensitized solar cell (DSSC) has also been explored. We have demonstrated that the overall efficiency of a ZnO NP-based solar cell significantly depends on the presence of high-energy photons in the solar radiation. In a control experiment on a model TiO 2 NP-based solar cell it has been demonstrated that the presence of high-energy photon has a minimal effect on the performance of the cell as the TiO 2 NPs are incapable of harvesting high-energy photons from solar radiation. The possibility of the back electron transfer from the excited NPs to the SD has also been investigated by studying the NPs in the presence of an ideal electron accepting organic molecule, benzoquinone (BQ). The time constants and nonradiative rate constant obtained for the ZnO/N719 system are found to be different from those of the ZnO/BQ system, which rules out the possibility of back electron transfer from ZnO NPs to SD N719. Moreover, the observed FRET dynamics in the light harvesting process of the nanocrystalites may be efficient in the further use of the nanoparticles in the development of new photodevices.
The Journal of Physical Chemistry B, 2010
The intrinsic fluorescent amino acid tryptophan is the unanimous choice for the spectroscopic inv... more The intrinsic fluorescent amino acid tryptophan is the unanimous choice for the spectroscopic investigation of proteins. However, several complicacies in the interpretation of tryptophan fluorescence in a protein are inevitable and an alternative intrinsic protein probe is a longstanding demand. In this contribution, we report an electron-transfer reaction in a human transporter protein (HSA) cavity which causes the tryptophan residue (Trp214) to undergo chemical modification to form one of its metabolites kynurenine (Kyn214). Structural integrity upon modification of the native protein is confirmed by dynamic light scattering (DLS) as well as near and far circular dichroism (CD) spectroscopy. Femtosecond-resolved fluorescence transients of the modified protein describe the dynamics of solvent molecules in the protein cavity in both the native and denatured states. In order to establish general use of the probe, we have studied the dipolar interaction of Kyn214 with a surface-bound ligand (crystal violet, CV) of the protein. By using the sensitivity of FRET, we have determined the distance between Kyn214 (donor) and CV (acceptor). Our study is an attempt to explore an alternative intrinsic fluorescence probe for the spectroscopic investigation of a protein. In order to establish the efficacy of the modification technique we have converted the tryptophan residues of other proteins (bovine serum albumin, chymotrypsin and subtilisin Carlsberg) to kynurenine and confirmed their structural integrity. We have also shown that catalytic activity of the enzymes remains intact upon the modification.
Physical Chemistry Chemical Physics, 2011
Improving the performance of photoactive solid-state devices begins with systematic studies of th... more Improving the performance of photoactive solid-state devices begins with systematic studies of the metal-semiconductor nanocomposites (NCs) upon which such devices are based. Here, we report the photo-dependent excitonic mechanism and the charge migration kinetics in a colloidal ZnO-Au NC system. By using a picosecond-resolved Fo¨rster resonance energy transfer (FRET) technique, we have demonstrated that excited ZnO nanoparticles (NPs) resonantly transfer visible optical radiation to the Au NPs, and the quenching of defect-mediated visible emission depends solely on the excitation level of the semiconductor. The role of the gold layer in promoting photolytic charge transfer, the activity of which is dependent upon the degree of excitation, was probed using methylene blue (MB) reduction at the semiconductor interface. Incident photon-tocurrent efficiency measurements show improved charge injection from a sensitizing dye to a semiconductor electrode in the presence of gold in the visible region. Furthermore, the short-circuit current density and the energy conversion efficiency of the ZnO-Au NP based dye-sensitized solar cell (DSSC) are much higher than those of a DSSC comprised of only ZnO NP. Our results represent a new paradigm for understanding the mechanism of defect-state passivation and photolytic activity of the metal component in metal-semiconductor nanocomposite systems.
Nanotechnology, 2010
We have explored light harvesting of the complex of ZnO nanoparticles with the biological probe O... more We have explored light harvesting of the complex of ZnO nanoparticles with the biological probe Oxazine 1 in the near-infrared region using picosecond-time-resolved fluorescence decay studies. We have used ZnO nanoparticles and Oxazine 1 as a model donor and acceptor, respectively, to explore the efficacy of the Förster resonance energy transfer (FRET) in the nanoparticle-dye system. It has been shown that FRET from the states localized near the surface and those in the bulk of the ZnO nanoparticles can be resolved by measuring the resonance efficiency for various wavelengths of the emission spectrum. It has been observed that the states located near the surface for the nanoparticles (contributing to visible emission at λ ≈ 550 nm) can contribute to very high efficiency (>90%) FRET. The efficiency of light harvesting dynamics of the ZnO nanorods has also been explored in this study and they were found to have much less efficiency (∼40%) for energy transfer compared to the nanoparticles. The possibility of an electron transfer reaction has been ruled out from the picosecond-resolved fluorescence decay of the acceptor dye at the ZnO surface.
Nanoscale, 2010
We report molecular functionalization of the promising manganite nanoparticles La 0.67 Sr 0.33 Mn... more We report molecular functionalization of the promising manganite nanoparticles La 0.67 Sr 0.33 MnO 3 (LSMO) for their solubilization in aqueous environments. The functionalization of individual NPs with the biocompatible citrate ligand, as confirmed by Fourier transform infrared (FTIR) spectroscopy, reveals that citrates are covalently attached to the surface of the NPs. UV-VIS spectroscopic studies on the citrate functionalized NPs reveals an optical band in the visible region. Uniform size selectivity (2.6 nm) of the functionalization process is confirmed from high resolution transmission electron microscope (HRTEM). In the present study we have used the optical band of the functionalized NPs to monitor their interaction with other biologically important ligands. F€ orster resonance energy transfer (FRET) of a covalently attached probe 4-nitrophenylanthranilate (NPA) with the capped NPs confirm the attachment of the NPA ligands to the surface functional group (-OH) of the citrate ligand. The FRET of a DNA base mimic, 2-aminopurine (2AP), with the NPs confirms the surface adsorption of 2AP. Our study may find relevance in the study of the interaction of individual manganite NPs with drug/ligand molecules.
Journal of Photochemistry and Photobiology B: Biology, 2011
Although rifampicin (Rf) is one of the most effective antibiotics against infection caused by Myc... more Although rifampicin (Rf) is one of the most effective antibiotics against infection caused by Mycobacterium tuberculosis, interaction of the drug with universal carrier protein in human blood plasma is not fully understood. Reduction of medicinal efficacy of other drugs, including anti-thrombosis drug warfarin (Wf), to the patients on Rf therapy also needs molecular understanding. In the present work we have studied interaction of Rf with one of the model carrier protein (human serum albumin). By using circular dichroism (CD) spectroscopy we have characterized the change in the secondary structure of the protein. The consequence of the simultaneous binding of the two drugs, Rf and Wf, on the structure of the protein has also been explored. Picosecond resolved Förster resonance energy transfer (FRET) from Wf to Rf explores possible binding sites of the anti-tuberculosis drug on the protein. In this report, we have discussed the potential problem of using the single tryptophan of the protein (Trp 214) as energy donor in FRET experiment for the characterization of the binding site of the drug Rf on the protein.
ACS Applied Materials & Interfaces, 2012
Light-harvesting nanohybrids (LHNs) are systems composed of an inorganic nanostructure associated... more Light-harvesting nanohybrids (LHNs) are systems composed of an inorganic nanostructure associated with an organic pigment that have been exploited to improve the light-harvesting performance over individual components. The present study is focused on developing a potential LHN, attained by the functionalization of dense arrays of ZnO nanorods (NRs) with a biologically important organic pigment hematoporphyrin (HP), which is an integral part of red blood cells (hemoglobin). Application of spectroscopic techniques, namely, Fourier transform infrared spectroscopy (FTIR) and Raman scattering, confirm successful monodentate binding of HP carboxylic groups to Zn 2+ located at the surface of ZnO NRs. Picosecond-resolved fluorescence studies on the resulting HP−ZnO nanohybrid show efficient electron migration from photoexcited HP to the host ZnO NRs. This essential photoinduced event activates the LHN under sunlight, which ultimately leads to the realization of visible-light photocatalysis (VLP) of a model contaminant Methylene Blue (MB) in aqueous solution. A control experiment in an inert gas atmosphere clearly reveals that the photocatalytic activity is influenced by the formation of reactive oxygen species (ROS) in the media. Furthermore, the stable LHNs prepared by optimized dye loading have also been used as an active layer in dye-sensitized solar cells (DSSCs). We believe these promising LHNs to find their dual applications in organic electronics and for the treatment of contaminant wastewater.
Physical chemistry chemical physics : PCCP, Jan 8, 2017
The Z-Scheme function within molecular systems has been rarely reported for solar energy conversi... more The Z-Scheme function within molecular systems has been rarely reported for solar energy conversion although it offers the possibility to achieve higher efficiency than single photon absorber photosystems due to the use of a wider range of visible light. In this study, we synthesized and investigated the electrochemical and spectroscopic properties of two new dyads based on ruthenium and osmium tris-bipyridine complexes covalently linked via a butane bridge to explore their ability to realize the Z-scheme function once immobilized on TiO2. These dyads can be grafted onto a nanocrystalline TiO2 film via the osmium complex bearing two dicarboxylic acid bipyridine ligands, while the ruthenium complex contains either two unsubstituted bipyridine ancillary ligands (RuH-Os) or two (4,4'-bis-trifluoromethyl-bipyridine) ancillary ligands (RuCF3-Os). Transient absorption spectroscopy studies of the Ru(ii)-Os(iii) dyads with femtosecond and nanosecond lasers were conducted both in solutio...
Journal of Fluorescence, 2010
The control of the spontaneous emission (SE) rate of dye molecules (4-dicyanomethylene-2-methyl-6... more The control of the spontaneous emission (SE) rate of dye molecules (4-dicyanomethylene-2-methyl-6p-dimethylaminostyryl-4H-pyran (DCM) and Coumarin 523 (C523)) embedded in the Porous Silicon (PS) matrix has been studied using picosecond resolved fluorescence decay and polarization studies. We have shown that the SE rates of the two organic dyes embedded in the PS matrix depend on the relative positions of the emission maxima of the dyes with respect to electronic band gap energy of the PS matrix. We have also explored that the electronic band gap of the host PS matrix can easily be tuned by partial oxidation of the PS and the nature of SE of the embedded dyes can be tuned accordingly. The demonstrated retardation or enhancement of the spontaneous photon emission may enable the application of fluorescent organic molecules in PS matrix in several quantum optical devices including the realization of single photon sources.
Journal of the American Chemical Society, 2016
Table of Contents A. General methods S2 B. Synthetic procedures S3 C. Physico-chemical characteri... more Table of Contents A. General methods S2 B. Synthetic procedures S3 C. Physico-chemical characterizations S12 C1. Electronic absorption and emission properties S12 C2. Electrochemical properties S12 C3. Charge transfer driving forces S13 C4. Spectroelectrochemistry S14 D. Transient absorption and photoemission experiments S15 E. Estimation of the maximum collapse probability S21 F. Spectra confirming purity and identity of new compounds S26 G. References S39 Scheme S2: Synthetic route for the Bodipy-NDI dyad and dyad 13.
In this article, we will review our investigation on the key ultrafast processes in the light har... more In this article, we will review our investigation on the key ultrafast processes in the light harvesting dynamics of Zinc Oxide (ZnO)-based nanomaterials. Firstly, we describe our studies on light harvesting of the complex of ZnO nanoparticles (NPs) with biological probe Oxazine 1 in the near-infrared region using time picosecond-resolved fluorescence decay studies. We have used ZnO NPs and Oxazine 1 as model donor and acceptor respectively to explore the efficacy of the Förster resonance energy transfer (FRET) in the nanoparticle-dye system. It has been shown that FRET from the states localized near the surface and those in the bulk of the ZnO NPs can be resolved by measuring the resonance efficiency for various wavelengths of the emission spectrum. It has been observed that the states located near the surface for the NPs (contributing to visible emission at 550 nm) can contribute to very high efficiency (>90%) FRET. The efficiency of light harvesting dynamics of the ZnO nanorods (NRs) has also been explored in this study and they were found to have much less efficiency (~40%) for energy transfer compared to the NPs. The possibility of electron transfer reaction has ruled out from the picosecond-resolved fluorescence decay of the acceptor dye at the ZnO surface. Secondly, we report the dynamics of light harvesting of ZnO NPs to a surface adsorbed sensitizing dye (SD) N719 (Ditetrabutylammonium cis-bis(isothiocyanato)bis(2,2'-bipyridyl-4,4'dicarboxylato)ruthenium(II)). By using picoseconds-resolved FRET technique we have explored that the excited ZnO NPs resonantly transfer visible optical radiation to the SD N719. The consequence of the energy transfer on the performance of the overall efficiency of a model ZnO NP
Beilstein Journal of Nanotechnology, 2013
In recent years, nanotechnology has gained significant interest for applications in the medical f... more In recent years, nanotechnology has gained significant interest for applications in the medical field. In this regard, a utilization of the ZnO nanoparticles for the efficient degradation of bilirubin (BR) through photocatalysis was explored. BR is a water insoluble byproduct of the heme catabolism that can cause jaundice when its excretion is impaired. The photocatalytic degradation of BR activated by ZnO nanoparticles through a non-radiative energy transfer pathway can be influenced by the surface defect-states (mainly the oxygen vacancies) of the catalyst nanoparticles. These were modulated by applying a simple annealing in an oxygen-rich atmosphere. The mechanism of the energy transfer process between the ZnO nanoparticles and the BR molecules adsorbed at the surface was studied by using steady-state and picosecond-resolved fluorescence spectroscopy. A correlation of photocatalytic degradation and time-correlated single photon counting studies revealed that the defect-engineered...
Springer Series in Materials Science, 2013
From the prevalent interest in the advancement of renewable energy sources, dye-sensitized solar ... more From the prevalent interest in the advancement of renewable energy sources, dye-sensitized solar cells (DSSCs) have emerged as one of the front running prospects due mainly to a constructive balance between cost and efficiency. In this chapter, we will review our works on the utility of using Förster resonance energy transfer (FRET) in the light harvesting dynamics of zinc oxide (ZnO)-based nanomaterials, which has recently shown promise for significant improvement in various aspects of photoelectrochemical cells. Firstly, we have used ZnO nanoparticles (NPs) and Oxazine 1 as model donor and acceptor, respectively, to investigate the key ultrafast process of FRET in the NP-dye system. The consequence of the energy transfer on the performance of a model ZnO NP-based DSSC has also been explored by using well-known Ruthenium-based sensitizers N719 attached to ZnO NPs offering as an intrinsic co-sensitizer. By using a picosecondresolved FRET technique, we have also demonstrated the role of the gold layer in promoting photoinduced charge transfer from ZnO-Au nanocomposite to a model contaminant methylene blue (MB). Due to the formation of the Schottky barrier at the ZnO-Au interface and the higher optical absorptions of the ZnO-Au photoelectrodes arising from the surface plasmon absorption of the Au NPs, enhanced power-conversion efficiency was achieved compared to bare ZnO-based DSSCs. Finally, potential co-sensitization of extrinsic sensitizer CdTe quantum dots (QDs) in ZnO nanorod (NR)-based DSSCs has been established where we have shown two major pathways by which CdTe QDs may contribute to the net photocurrent in a DSSC: (1) a direct injection of charge carriers from QDs
The Journal of Physical Chemistry C, 2010
Capping or functionalization of semiconductor quantum dots (QDs) is unavoidable for their photost... more Capping or functionalization of semiconductor quantum dots (QDs) is unavoidable for their photostability in practical use including sensitizer and biological tagging agents. However, the efficiency of the electron/hole transport from the photoexcited QDs to the external environments across ...
The Journal of Physical Chemistry C, 2012
Different-sized, 3-mercaptopropionic acid (MPA) stabilized CdTe quantum dots (QDs) have been prep... more Different-sized, 3-mercaptopropionic acid (MPA) stabilized CdTe quantum dots (QDs) have been prepared in aqueous solution, and potential cosensitization of such QDs in ZnO nanorod (NR)-based dye-sensitized solar cells (DSSCs) has been established. The results presented in this study highlight two major pathways by which CdTe QDs may contribute to the net photocurrent in a DSSC: (1) a direct injection of charge carriers from QDs to ZnO semiconductor via photoinduced electron transfer (PET) and (2) an indirect excitation of the sensitizing dye (SD) N719 molecules by funneling harvested light via Forster resonance energy transfer (FRET). The steady-state and picosecond-resolved luminescence measurements were combined to clarify the process of PET and FRET from the excited QDs to ZnO NR and SD N719, respectively. On the basis of these advantages, the short-circuit current density and the photoconductivity of the QD-assembled DSSCs with distinct architectures are found to be much higher than DSSCs fabricated with N719 sensitizer only. 49 Many efforts have been made to introduce stronger light 50 absorber and to widen the spectral response of the photo-51 sensitizers. In recent times, the use of QDs as light harvesters 52 has stimulated a lot of interest because of its higher extinction 53 coefficient compared to conventional dyes 10 for efficient light 54 energy conversion. 11−14 Because of the size quantization 55 property, the optical and electronic properties of the semi-56 conductor QDs can be engineered to further tune the response 57 of quantum dot solar cells (QDSCs). 15−17 In addition, QDs 58 open up new possibilities for the utilization of hot electrons 18 59 or multiple charge carrier generation with a single photon. 19 60 Multiple carrier generation in PbSe nanocrystals has shown that 61 two or more excitons can be generated with a single photon of 62 energy greater than the band gap. 20 The performance of a 63 QDSC is currently limited by several factors, including a limited 64 choice of electrolytes with which QDs are chemically 65 compatible, insufficient passivation of recombination channels 66 (usually attributed to surface traps), and limited QD loading 67 capacities. 21 Recent studies have shown that it is possible to
The Journal of Physical Chemistry C, 2012
Bilirubin (BR) is a protective antioxidant; however, when its conjugation and excretion are impai... more Bilirubin (BR) is a protective antioxidant; however, when its conjugation and excretion are impaired, as in neonatal and hereditary jaundice, BR accumulates and may cause severe neurotoxicity. Here, we report a novel mechanism for ZnO nanoparticle (NP)-sensitized BR degradation via defect-mediated nonradiative energy transfer pathway. Among different sizes and shapes, ZnO particles with diameter of 5 nm having very high concentration of defect states are found to be the most effective catalyst, which particularly follows a pseudofirst-order kinetics validating the Langmuir−Hinshelwood model of surface catalysis. The nontoxic wide band gap ZnO NPs essentially transmit defect-mediated visible optical radiation, which is not supposed to interfere with the conventional phototherapy process. Therefore, the recyclable ZnO nanocatalysts essentially invite an added advantage in potential therapeutic applications and/or in a flow-device that has been explored in the present study.
Photochemistry and Photobiology, 2012
In this contribution, we report studies on the interaction of an antituberculosis drug rifampicin... more In this contribution, we report studies on the interaction of an antituberculosis drug rifampicin (RF) in a macromolecular assembly of CTAB with an extrinsic fluorescent probe, dansyl chloride (DC). The absorption spectrum of the drug RF has been employed to study Fo¨rster resonance energy transfer (FRET) from DC, bound to the CTAB micelle using picosecond resolved fluorescence spectroscopy. We have applied a kinetic model developed by Tachiya to understand the kinetics of energy transfer and the distribution of acceptor (RF) molecules around the donor (DC) molecules in the micellar surface with increasing quencher concentration. The mean number of RF molecules associated with the micelle increases from 0.24 at 20 lM M RF concentration to 1.5 at 190 lM M RF concentration and consequently the quenching rate constant (k q) due to the acceptor (RF) molecules increases from 0.23 to 0.75 ns)1 at 20 and 190 lM M RF concentration, respectively. However, the mean number of the quencher molecule and the quenching rate constant does not change significantly beyond a certain RF concentration (150 lM M), which is consistent with the results obtained from time resolved FRET analysis. Moreover, we have explored the diffusion controlled FRET between DC and RF, using microfluidics setup, which reveals that the reaction pathway follows one-step process.
Nanotechnology, 2012
Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes es... more Free-standing, bi-directionally permeable and ultra-thin anodic aluminum oxide (AAO) membranes establish attractive templates (host) for the synthesis of nano-dots and rods of various materials (guest). This is due to their chemical and structural integrity and high periodicity on length scales of 5-150 nm which are often used to host photoactive nano-materials for various device applications including dye-sensitized solar cells. In the present study, AAO membranes are synthesized by using electrochemical methods and a detailed structural characterization using FEG-SEM, XRD and TGA confirms the porosity and purity of the material. Defect-mediated photoluminescence quenching of the porous AAO membrane in the presence of an electron accepting guest organic molecule (benzoquinone) is studied by means of steady-state and picosecond/femtosecond-resolved luminescence measurements. Using time-resolved luminescence transients, we have also revealed light harvesting of complexes of porous alumina impregnated with inorganic quantum dots (Maple Red) or gold nanowires. Both the Förster resonance energy transfer and the nano-surface energy transfer techniques are employed to examine the observed quenching behavior as a function of the characteristic donor-acceptor distances. The experimental results will find their relevance in light harvesting devices based on AAOs combined with other materials involving a decisive energy/charge transfer dynamics.
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Papers by abhinandan makhal