Hirendra Ghosh | Homi Bhabha National Institute (HBNI, BARC, MUMBAI) (original) (raw)
Papers by Hirendra Ghosh
EPJ Web of Conferences, 2013
Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part... more Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part in an ultrafast electron transfer (ET) reaction in electron-donating triethylamine solvent, but that ultrafast proton coupled electron transfer (PCET) occurs in diethylamine solvent.
The Journal of Physical Chemistry C, 2013
High resolution TEM images of ZrO 2 nanoparticles. SI Figure 1: The HRTEM image of synthesized Zr... more High resolution TEM images of ZrO 2 nanoparticles. SI Figure 1: The HRTEM image of synthesized ZrO 2 nanoparticles. Particle size wsa measured to be 4 nm. Inset: The SAED pattern of ZrO 2 nanoparticles.
The Journal of Physical Chemistry C, 2015
ABSTRACT Ultrafast charge-transfer dynamics has been demonstrated in CdSe quantum dots (QD) using... more ABSTRACT Ultrafast charge-transfer dynamics has been demonstrated in CdSe quantum dots (QD) using two Re(I)?polypyridyl complexes having pendent catechol (Re1,2) and resorcinol (Re1,3) as the sensitizer molecules. Energy level diagram of CdSe QD and Re1,2 and Re1,3 sensitizer reveals that photo-excited hole of CdSe QD can be transferred to both Re1,2 and Re1,3 molecule and photoexcited Re1,2 and Re1,3 can inject electron in the conduction band which has been confirmed by steady state and time-resolved photoluminescence studies with selective photo-excitation. Femtosecond transient absorption studies have been carried out to monitor charge transfer dynamics in early time scale. Transient absorption spectra shows formation of cation radicals for both Re1,2 and Re1,3 in 550 ? 650 nm region with a peak at 590 nm region and broad absorption in 650 -1000 nm region which can be attributed to photoexcited electron in conduction band of CdSe QD. Charge recombination was determined by monitoring the decay of cation radials as well decay of electron and found to be slower in Re1,3/CdSe system as compared to that of Re1,2/CdSe system which due to weaker electronic coupling in the former system.
EPJ Web of Conferences, 2013
Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part... more Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part in an ultrafast electron transfer (ET) reaction in electron-donating triethylamine solvent, but that ultrafast proton coupled electron transfer (PCET) occurs in diethylamine solvent. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The journal of physical chemistry letters, Jan 21, 2011
Photosynthetic antenna complexes exhibit unidirectional energy-transport phenomena, which make th... more Photosynthetic antenna complexes exhibit unidirectional energy-transport phenomena, which make them potential photosensitizers in interfacial electron-transfer processes. In the present study, we show the antenna function of phycocyanin-allophycocyanin (PC-APC) complex using transient emission and absorption spectroscopy. Interfacial electron-transfer dynamics in the PC-APC complex sensitized ZnO semiconductor quantum dot material is compared in native and denatured conditions. The downhill sequential energy transfer from a peripheral phycocyanin disk to a core allophycocyanin disk opens a new electron injection pathway from the allophycocyanin disk in addition to primary electron injection from directly photoexcited phycocyanin disk. Further, the large association of phycocayanobilin chromophores in PC-APC conjugates stabilizes the positive charge within the sensitizer, which leads to slower charge recombination in comparison to that in denatured condition. This study displays the ...
The journal of physical chemistry letters, Jan 19, 2012
A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesti... more A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesting applications. This porphyrin aggregate enables control of energy dissipation of coherent excited states by changing the self-assembly pattern. New exciton spectral features create a new route of energy transfer in this porphyrin aggregate. The kinetic model of exciton state decay is addressed in this Perspective by reporting steady-state and transient emission and absorption studies of porphyrin J- and H-aggregates. The porphyrin J-aggregate emerges with better spectral coverage and exciton dynamics, which are suitable for light-harvesting antenna functions. This motif is explored in a photosensitization study of TiO2 semiconductor materials. The transient absorption studies show that the J-aggregate improves the photoinduced charge separation at the porphyrin/TiO2 interface. The higher charge separation is attributed to exciton-coupled charge-transfer processes in porphyrin J-aggrega...
Journal of Physical Chemistry B, 1999
The photophysics and electron injection dynamics of Ru(dcbpy) 2 (NCS) 2 [dcbpy ) (4,4′-dicarboxy-... more The photophysics and electron injection dynamics of Ru(dcbpy) 2 (NCS) 2 [dcbpy ) (4,4′-dicarboxy-2,2′bipyridine)] (or Ru N3) in solution and adsorbed on nanocrystalline Al 2 O 3 and TiO 2 thin films were studied by femtosecond mid-IR spectroscopy. For Ru N3 in ethanol after 400 nm excitation, the long-lived metalto-ligand charge transfer ( 3 MLCT) excited state with CN stretching bands at 2040 cm -1 was formed in less than 100 fs. No further decay of the excited-state absorption was observed within 1 ns consistent with the previously known 59 ns lifetime. For Ru N3 absorbed on Al 2 O 3 , an insulating substrate, the 3 MLCT state was also formed in less than 100 fs. In contrast to Ru N3 in ethanol, this excited state decayed by 50% within 1 ns via multiple exponential decay while no ground-state recovery was observed. This decay is attributed to electron transfer to surface states in the band gap of Al 2 O 3 nanoparticles. For Ru N3 adsorbed onto the surface of TiO 2 , the transient mid-IR signal was dominated by the IR absorption of injected electrons in TiO 2 in the 1700-2400 cm -1 region. The rise time of the IR signal can be fitted by biexponential rise functions: 50 ( 25 fs (>84%) and 1.7 ( 0.5 ps (<16%) after deconvolution of instrument response function determined in a thin silicon wafer. Because of the scattering of the pump photon in the porous TiO 2 thin film, the instrument response may be slightly lengthened, which may require a faster rise time for the first component to fit the data. The first component is assigned to the electron injection from the Ru N3 excited state to TiO 2 . The amplitude of the slower component appears to vary with samples ranging from ca. 16% in new samples to <5% in aged samples. The subsequent dynamics of the injected electrons have also been monitored by the decay of the IR signal. The observed 20% decay in amplitude within 1 ns was attributed to electron trapping dynamics in the thin films.
![Research paper thumbnail of Dynamics of Electron Injection in Nanocrystalline Titanium Dioxide Films Sensitized with [Ru(4,4‘-dicarboxy-2,2‘-bipyridine) 2 (NCS) 2 ] by Infrared Transient Absorption](https://attachments.academia-assets.com/41608808/thumbnails/1.jpg)
](Journal of Physical Chemistry B, 1998
We have used femtosecond pump-probe spectroscopy to time resolve the injection of electrons into ... more We have used femtosecond pump-probe spectroscopy to time resolve the injection of electrons into nanocrystalline TiO 2 film electrodes under ambient conditions following photoexcitation of the adsorbed dye, [Ru(4,4′-dicarboxy-2,2′-bipyridine) 2 (NCS) 2 ] (N3). Pumping at one of the metal-to-ligand charge-transfer absorption peaks and probing the absorption by injected electrons in the TiO 2 at 1.52 µm and in the range of 4.1-7.0 µm, we have directly observed the arrival of electrons injected into the TiO 2 film. Our measurements indicate an instrument-limited ∼50 fs upper limit on the electron injection time. We have compared the infrared transient absorption for noninjecting systems consisting of N3 in ethanol and N3 adsorbed to films of nanocrystalline Al 2 O 3 and ZrO 2 and found no indication of electron injection at probe wavelengths in the mid-IR (4.1-7.0 µm).
Journal of The American Chemical Society, 1993
... Complexes Studied by Picosecond Pump Probe Spectroscopy Hirendra N. Ghosh, Haridas Pal, Avina... more ... Complexes Studied by Picosecond Pump Probe Spectroscopy Hirendra N. Ghosh, Haridas Pal, Avinash V. Sapre, and Jai P. Mittal' Contribution from the Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay 400085, India Received May 13, 1993" ...
The Journal of Physical Chemistry, 1996
The unusual solvatochromism of Cââ is investigated in a variety of solvent mixtures by optical ab... more The unusual solvatochromism of Cââ is investigated in a variety of solvent mixtures by optical absorption and fluorescence techniques. Distinct reversible color change from pink to purple is seen in the solvent mixtures studied. Such changes are seen also for Cââ solutions in some solvent mixtures. Formation of clusters is found to be responsible for the observed optical changes. Light
Journal of the Chemical Society, Faraday Transactions, 1996
Formation of radical adducts of Cs0 with alkyl and halo-alkyl radicals ... Transient absorption a... more Formation of radical adducts of Cs0 with alkyl and halo-alkyl radicals ... Transient absorption and emission characteristics of the adducts ... Hirendra N. Ghosh, Haridas Pal, Avinash V. Sapre,* Tulsi Mukherjee and Jai P. Mittal Chemistry Division, Bhabha Atomic Research ...
Journal of Physical Chemistry B, 2007
We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalentl... more We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalently coupled to a redox active Mo center, MoL*(NO)Cl(X) (L* is the face-capping tridentate ligand tris(3,5-dimethylpyrazolyl) hydroborate and X is a phenoxide/pyridyl/amido derivative of porphyrin). The luminescence quantum yields of the bichromophoric systems (1, 2, and 5) were found to be an order of magnitude less than those of their respective porphyrin precursors. Transient absorption measurements revealed the formation of the porphyrin radical cation species (P(.)(+)) and photoinduced electron transfer from the porphyrin moiety to the respective Mo center in 1, 2, and 5. Electrochemical studies showed that the reduction potentials of the acceptor Mo centers in a newly synthesized pyridyl derivative (2; E(1/2)[Mo(I/0)] = approximately -1.4 V vs Ag/AgCl) and previously reported phenoxy- (1; E(1/2)[Mo(II/I)] = approximately -0.3 V vs Ag/AgCl) and amido- (3; E(1/2)[Mo(II/I)] = approximately -0.82 V vs Ag/AgCl) derivatives were varied over a wide range. Thus, studies with these complexes permitted us to correlate the probable effect of this potential gradient on the electron-transfer dynamics. Time-resolved absorption studies, following excitation at the Soret band of the porphyrin fragment in complexes 1, 2, and 5, established that forward electron transfer took place biexponentially from both S2 and S1 states of the porphyrin center to the Mo moiety with time constants 150-250 fs and 8-20 ps, respectively. In the case of MoL*(NO)ClX (where X is pyridine derivative 2), the high reduction potential for the MoI/0 couple allowed electron transfer solely from the S2 state of the porphyrin center. Time constants for the charge recombination process for all complexes were found to be 150-300 ps. Further, electrochemical and EPR studies with the trichromophoric complexes (3 and 4) revealed that the orthogonal orientation of the peripheral phenoxy/pyridyl rings negated the possibility of any electronic interaction between two paramagnetic Mo centers in the ground state and thereby the spin exchange, which otherwise was observed for related Mo complexes when two Mo centers are separated by a polyene system with comparable or larger separation distances.
19th International Conference on Ultrafast Phenomena, 2014
Ultrafast Electron cooling dynamics of highly luminescent oleic acid caped CdS x Se 1-x alloy qua... more Ultrafast Electron cooling dynamics of highly luminescent oleic acid caped CdS x Se 1-x alloy quantum dot (QD) is investigated by femtosecond transient absorption studies and found to be much slower as compared to pure CdSe and CdS QDs.
The journal of physical chemistry. B, Jan 25, 2006
Femtosecond transient absorption spectroscopy has been employed to understand the excited state d... more Femtosecond transient absorption spectroscopy has been employed to understand the excited state dynamics of [Ru(bpy)(2)Sq](+) (I; bpy is 2,2'-bipyridyl, and Sq is the deprotonated species of the semiquinone form of 1,2-dihydroxy benzene) and its derivatives, a widely studied near-infrared (NIR) active electrochromic dye. Apart from the well-defined dpi(Ru) --> pi(bpy)-based metal-to-ligand charge transfer (MLCT) transition bands at approximately 480 nm, this class of molecules generally shows another dpi(Ru) --> pi(Sq)(SOMO)-based intense MLCT band at around 900 nm, which is known to be redox active and bleaches reversibly upon a change in the oxidation state of the coordinated dioxolene moiety. To have better insight into the photoinduced electron transfer dynamics associated with this MLCT transition, detailed investigations have been carried out on exciting this MLCT band at 800 nm. Immediately after photoexcitation, bleach at 900 nm has been observed, whose recovery is...
The Journal of Physical Chemistry C, 2009
We have investigated the interfacial electron-transfer dynamics in ultrasmall TiO 2 nanoparticles... more We have investigated the interfacial electron-transfer dynamics in ultrasmall TiO 2 nanoparticles sensitized by alizarin using a femtosecond transient absorption technique. Electron injection has been confirmed by direct detection of the electron in the conduction band and cation radical of the adsorbed dye as monitored by transient absorption spectroscopy in the visible and near-IR region. The electron injection event was followed by monitoring the formation of the dye cation at 550 nm and also the conduction band electron at 900 nm, which revealed a multiexponential dynamics with time constants of 100 fs and 17 and 50 ps. This observation was explained on the basis of discreteness of the conduction band levels due to the finite size effect of the nanoparticle. The multiexponential injection indicated the event to be nonadiabatic contrary to debated literature reports. The back electron-transfer (BET) dynamics followed at the same wavelength revealed a fast component of value 0.2 ps and very slow BET time of >1 ns. The comparison with previous reports on bulk TiO 2 revealed a very slow BET in the present case which has been explained within the framework of Marcus theory. The result gives us direct proof of a nonadiabatic electron-transfer reaction in a strong binding dye like alizarin.
The Journal of Physical Chemistry C, 2010
We are reporting ultrafast charge carrier and charge transfer dynamics of the CdTe quantum dot (Q... more We are reporting ultrafast charge carrier and charge transfer dynamics of the CdTe quantum dot (QD) and type II CdTe/CdS core−shell QD materials with different shell (CdS) thicknesses. Herein, we have synthesized CdTe and CdTe/CdS core−shell quantum dots ...
Journal of Physical Chemistry C, 2008
We report synthesis of a new catechol derivative of 2,2′-bipyridyl (L 1 ) and two new Os(II)-poly... more We report synthesis of a new catechol derivative of 2,2′-bipyridyl (L 1 ) and two new Os(II)-polypyridyl complexes, I and II, with pendant catechol functionality (Scheme 1). Both complexes show two strong metalto-ligand charge transfer (MLCT) absorption bands in the visible region that are attributed to 1 MLCT (spin allowed) and 3 MLCT (spin forbidden) transitions. We have recorded photoluminescence spectra for both complexes at room temperature and at 77 K. We have determined the lifetime for the excited triplet ( 3 MLCT) states using time-resolved emission spectroscopy. Optical absorption studies reveal that both the complexes I and II form charge transfer (CT) complex with TiO 2 and ZrO 2 (higher band gap) nanoparticles. Photoinduced electron injection takes place from the Os(II)-complexes to the conduction band of TiO 2 and surface states of ZrO 2 nanoparticles following excitation of the respective CT complexes. On recombination of these respective charge-separated complexes, CT emission has been detected in the above dye/nanoparticle systems. Monitoring the CT emission, we could determine back electron transfer (BET) rate for the charge recombination process.
The Journal of Physical Chemistry C, 2009
... Kar , Sandeep Verma , Amitava Das* and Hirendra N. Ghosh* . Radiation and Photo Chemis... more ... Kar , Sandeep Verma , Amitava Das* and Hirendra N. Ghosh* . Radiation and Photo Chemistry Division, Bhabha Atomic Research Center, Mumbai, India, and Central Salt and Marine Chemicals Research Institute (CSIR), Bhavnagar 364002, Gujarat, India. J. Phys. Chem ...
The Journal of Physical Chemistry B, 2010
The aggregation behavior of 5,10,15-trisphenyl-20-(3,4-dihydroxy phenyl) porphyrin (L) in aqueous... more The aggregation behavior of 5,10,15-trisphenyl-20-(3,4-dihydroxy phenyl) porphyrin (L) in aqueous solution has been studied as a function of pH and concentration with the help of steady state absorption and emission spectroscopy. Our studies revealed that, for a particular concentration range, molecules of L undergo a reversible aggregation process and form two different aggregates at two different pH ranges, namely, J- and H-aggregates. We have monitored the excited state lifetimes of different aggregates by picosecond time-resolved emission spectroscopy and found that the emission lifetime of L reduces drastically with the formation of these aggregates. To study the dynamics associated with the excited state of both non-aggregated and aggregated (both J and H) porphyrins in an ultrafast time domain, we have carried out femtosecond transient absorption spectroscopy in the visible region following excitation of the respective samples at 400 nm. In addition to other de-excitation channels, another extra 100 fs (major) component for H-aggregates and 200 fs (major) component for J-aggregates has been observed and attributed to the exciton decay components of the respective aggregates.
The Journal of Physical Chemistry B, 2006
Interfacial electron transfer (ET) dynamics of 5,10,15-trisphenyl-20-(3,4-dihydroxybenzene) porph... more Interfacial electron transfer (ET) dynamics of 5,10,15-trisphenyl-20-(3,4-dihydroxybenzene) porphyrin (TPP-cat) adsorbed on TiO2 nanoparticles has been studied by femtosecond transient absorption spectroscopy in the visible and near-IR region exciting at 400 and 800 nm. TPP-cat molecule forms a charge transfer (CT) complex with TiO2 nanoparticles through the catechol moiety with the formation of a five-membered ring. Optical absorption measurements have shown that the Q-band of TPP-cat interacts strongly with TiO2 due to chelation; however, the Soret band is affected very little. Optical absorption measurements indicate that the catechol moiety also interacts with TiO2 nanoparticles showing the characteristic band of pure catechol-TiO2 charge transfer (CT) in the visible region. Electron injection has been confirmed by monitoring the cation radical, instant bleach, and injected electron in the conduction band of TiO2 nanoparticles. Electron injection time has been measured to be &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 100 fs and recombination kinetics has been best fitted with a multiexponential function, where the majority of the injected electrons come back to the parent cation radical with a time constant of approximately 800 fs for both excitation wavelengths. However, the reaction channel for the electron injection process has been found to be different for both wavelengths. Excitation at 800 nm, found to populate the CT state of the Q-band, and from the photoexcited CT state electron injection into the conduction band, takes place through diffusion. On the other hand, with excitation at 400 nm, a complicated reaction channel takes place. Excitation with 400 nm light excites both the CT band of Cat-TiO2 and also the Soret band of TPP-cat. We have discussed the reaction path in the TPP-cat/TiO2 system after exciting with both 400 and 800 nm laser light. We have also compared ET dynamics by exciting at both wavelengths.
EPJ Web of Conferences, 2013
Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part... more Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part in an ultrafast electron transfer (ET) reaction in electron-donating triethylamine solvent, but that ultrafast proton coupled electron transfer (PCET) occurs in diethylamine solvent.
The Journal of Physical Chemistry C, 2013
High resolution TEM images of ZrO 2 nanoparticles. SI Figure 1: The HRTEM image of synthesized Zr... more High resolution TEM images of ZrO 2 nanoparticles. SI Figure 1: The HRTEM image of synthesized ZrO 2 nanoparticles. Particle size wsa measured to be 4 nm. Inset: The SAED pattern of ZrO 2 nanoparticles.
The Journal of Physical Chemistry C, 2015
ABSTRACT Ultrafast charge-transfer dynamics has been demonstrated in CdSe quantum dots (QD) using... more ABSTRACT Ultrafast charge-transfer dynamics has been demonstrated in CdSe quantum dots (QD) using two Re(I)?polypyridyl complexes having pendent catechol (Re1,2) and resorcinol (Re1,3) as the sensitizer molecules. Energy level diagram of CdSe QD and Re1,2 and Re1,3 sensitizer reveals that photo-excited hole of CdSe QD can be transferred to both Re1,2 and Re1,3 molecule and photoexcited Re1,2 and Re1,3 can inject electron in the conduction band which has been confirmed by steady state and time-resolved photoluminescence studies with selective photo-excitation. Femtosecond transient absorption studies have been carried out to monitor charge transfer dynamics in early time scale. Transient absorption spectra shows formation of cation radicals for both Re1,2 and Re1,3 in 550 ? 650 nm region with a peak at 590 nm region and broad absorption in 650 -1000 nm region which can be attributed to photoexcited electron in conduction band of CdSe QD. Charge recombination was determined by monitoring the decay of cation radials as well decay of electron and found to be slower in Re1,3/CdSe system as compared to that of Re1,2/CdSe system which due to weaker electronic coupling in the former system.
EPJ Web of Conferences, 2013
Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part... more Femtosecond infrared absorption studies strongly suggest that photoexcited 9-anthranol takes part in an ultrafast electron transfer (ET) reaction in electron-donating triethylamine solvent, but that ultrafast proton coupled electron transfer (PCET) occurs in diethylamine solvent. This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The journal of physical chemistry letters, Jan 21, 2011
Photosynthetic antenna complexes exhibit unidirectional energy-transport phenomena, which make th... more Photosynthetic antenna complexes exhibit unidirectional energy-transport phenomena, which make them potential photosensitizers in interfacial electron-transfer processes. In the present study, we show the antenna function of phycocyanin-allophycocyanin (PC-APC) complex using transient emission and absorption spectroscopy. Interfacial electron-transfer dynamics in the PC-APC complex sensitized ZnO semiconductor quantum dot material is compared in native and denatured conditions. The downhill sequential energy transfer from a peripheral phycocyanin disk to a core allophycocyanin disk opens a new electron injection pathway from the allophycocyanin disk in addition to primary electron injection from directly photoexcited phycocyanin disk. Further, the large association of phycocayanobilin chromophores in PC-APC conjugates stabilizes the positive charge within the sensitizer, which leads to slower charge recombination in comparison to that in denatured condition. This study displays the ...
The journal of physical chemistry letters, Jan 19, 2012
A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesti... more A porphyrin aggregate is reported that exhibits novel exciton state properties for light-harvesting applications. This porphyrin aggregate enables control of energy dissipation of coherent excited states by changing the self-assembly pattern. New exciton spectral features create a new route of energy transfer in this porphyrin aggregate. The kinetic model of exciton state decay is addressed in this Perspective by reporting steady-state and transient emission and absorption studies of porphyrin J- and H-aggregates. The porphyrin J-aggregate emerges with better spectral coverage and exciton dynamics, which are suitable for light-harvesting antenna functions. This motif is explored in a photosensitization study of TiO2 semiconductor materials. The transient absorption studies show that the J-aggregate improves the photoinduced charge separation at the porphyrin/TiO2 interface. The higher charge separation is attributed to exciton-coupled charge-transfer processes in porphyrin J-aggrega...
Journal of Physical Chemistry B, 1999
The photophysics and electron injection dynamics of Ru(dcbpy) 2 (NCS) 2 [dcbpy ) (4,4′-dicarboxy-... more The photophysics and electron injection dynamics of Ru(dcbpy) 2 (NCS) 2 [dcbpy ) (4,4′-dicarboxy-2,2′bipyridine)] (or Ru N3) in solution and adsorbed on nanocrystalline Al 2 O 3 and TiO 2 thin films were studied by femtosecond mid-IR spectroscopy. For Ru N3 in ethanol after 400 nm excitation, the long-lived metalto-ligand charge transfer ( 3 MLCT) excited state with CN stretching bands at 2040 cm -1 was formed in less than 100 fs. No further decay of the excited-state absorption was observed within 1 ns consistent with the previously known 59 ns lifetime. For Ru N3 absorbed on Al 2 O 3 , an insulating substrate, the 3 MLCT state was also formed in less than 100 fs. In contrast to Ru N3 in ethanol, this excited state decayed by 50% within 1 ns via multiple exponential decay while no ground-state recovery was observed. This decay is attributed to electron transfer to surface states in the band gap of Al 2 O 3 nanoparticles. For Ru N3 adsorbed onto the surface of TiO 2 , the transient mid-IR signal was dominated by the IR absorption of injected electrons in TiO 2 in the 1700-2400 cm -1 region. The rise time of the IR signal can be fitted by biexponential rise functions: 50 ( 25 fs (>84%) and 1.7 ( 0.5 ps (<16%) after deconvolution of instrument response function determined in a thin silicon wafer. Because of the scattering of the pump photon in the porous TiO 2 thin film, the instrument response may be slightly lengthened, which may require a faster rise time for the first component to fit the data. The first component is assigned to the electron injection from the Ru N3 excited state to TiO 2 . The amplitude of the slower component appears to vary with samples ranging from ca. 16% in new samples to <5% in aged samples. The subsequent dynamics of the injected electrons have also been monitored by the decay of the IR signal. The observed 20% decay in amplitude within 1 ns was attributed to electron trapping dynamics in the thin films.
Journal of Physical Chemistry B, 1998
We have used femtosecond pump-probe spectroscopy to time resolve the injection of electrons into ... more We have used femtosecond pump-probe spectroscopy to time resolve the injection of electrons into nanocrystalline TiO 2 film electrodes under ambient conditions following photoexcitation of the adsorbed dye, [Ru(4,4′-dicarboxy-2,2′-bipyridine) 2 (NCS) 2 ] (N3). Pumping at one of the metal-to-ligand charge-transfer absorption peaks and probing the absorption by injected electrons in the TiO 2 at 1.52 µm and in the range of 4.1-7.0 µm, we have directly observed the arrival of electrons injected into the TiO 2 film. Our measurements indicate an instrument-limited ∼50 fs upper limit on the electron injection time. We have compared the infrared transient absorption for noninjecting systems consisting of N3 in ethanol and N3 adsorbed to films of nanocrystalline Al 2 O 3 and ZrO 2 and found no indication of electron injection at probe wavelengths in the mid-IR (4.1-7.0 µm).
Journal of The American Chemical Society, 1993
... Complexes Studied by Picosecond Pump Probe Spectroscopy Hirendra N. Ghosh, Haridas Pal, Avina... more ... Complexes Studied by Picosecond Pump Probe Spectroscopy Hirendra N. Ghosh, Haridas Pal, Avinash V. Sapre, and Jai P. Mittal' Contribution from the Chemistry Division, Bhabha Atomic Research Centre, Trombay, Bombay 400085, India Received May 13, 1993" ...
The Journal of Physical Chemistry, 1996
The unusual solvatochromism of Cââ is investigated in a variety of solvent mixtures by optical ab... more The unusual solvatochromism of Cââ is investigated in a variety of solvent mixtures by optical absorption and fluorescence techniques. Distinct reversible color change from pink to purple is seen in the solvent mixtures studied. Such changes are seen also for Cââ solutions in some solvent mixtures. Formation of clusters is found to be responsible for the observed optical changes. Light
Journal of the Chemical Society, Faraday Transactions, 1996
Formation of radical adducts of Cs0 with alkyl and halo-alkyl radicals ... Transient absorption a... more Formation of radical adducts of Cs0 with alkyl and halo-alkyl radicals ... Transient absorption and emission characteristics of the adducts ... Hirendra N. Ghosh, Haridas Pal, Avinash V. Sapre,* Tulsi Mukherjee and Jai P. Mittal Chemistry Division, Bhabha Atomic Research ...
Journal of Physical Chemistry B, 2007
We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalentl... more We report new polychromophoric complexes, where different porphyrin (P) derivatives are covalently coupled to a redox active Mo center, MoL*(NO)Cl(X) (L* is the face-capping tridentate ligand tris(3,5-dimethylpyrazolyl) hydroborate and X is a phenoxide/pyridyl/amido derivative of porphyrin). The luminescence quantum yields of the bichromophoric systems (1, 2, and 5) were found to be an order of magnitude less than those of their respective porphyrin precursors. Transient absorption measurements revealed the formation of the porphyrin radical cation species (P(.)(+)) and photoinduced electron transfer from the porphyrin moiety to the respective Mo center in 1, 2, and 5. Electrochemical studies showed that the reduction potentials of the acceptor Mo centers in a newly synthesized pyridyl derivative (2; E(1/2)[Mo(I/0)] = approximately -1.4 V vs Ag/AgCl) and previously reported phenoxy- (1; E(1/2)[Mo(II/I)] = approximately -0.3 V vs Ag/AgCl) and amido- (3; E(1/2)[Mo(II/I)] = approximately -0.82 V vs Ag/AgCl) derivatives were varied over a wide range. Thus, studies with these complexes permitted us to correlate the probable effect of this potential gradient on the electron-transfer dynamics. Time-resolved absorption studies, following excitation at the Soret band of the porphyrin fragment in complexes 1, 2, and 5, established that forward electron transfer took place biexponentially from both S2 and S1 states of the porphyrin center to the Mo moiety with time constants 150-250 fs and 8-20 ps, respectively. In the case of MoL*(NO)ClX (where X is pyridine derivative 2), the high reduction potential for the MoI/0 couple allowed electron transfer solely from the S2 state of the porphyrin center. Time constants for the charge recombination process for all complexes were found to be 150-300 ps. Further, electrochemical and EPR studies with the trichromophoric complexes (3 and 4) revealed that the orthogonal orientation of the peripheral phenoxy/pyridyl rings negated the possibility of any electronic interaction between two paramagnetic Mo centers in the ground state and thereby the spin exchange, which otherwise was observed for related Mo complexes when two Mo centers are separated by a polyene system with comparable or larger separation distances.
19th International Conference on Ultrafast Phenomena, 2014
Ultrafast Electron cooling dynamics of highly luminescent oleic acid caped CdS x Se 1-x alloy qua... more Ultrafast Electron cooling dynamics of highly luminescent oleic acid caped CdS x Se 1-x alloy quantum dot (QD) is investigated by femtosecond transient absorption studies and found to be much slower as compared to pure CdSe and CdS QDs.
The journal of physical chemistry. B, Jan 25, 2006
Femtosecond transient absorption spectroscopy has been employed to understand the excited state d... more Femtosecond transient absorption spectroscopy has been employed to understand the excited state dynamics of [Ru(bpy)(2)Sq](+) (I; bpy is 2,2'-bipyridyl, and Sq is the deprotonated species of the semiquinone form of 1,2-dihydroxy benzene) and its derivatives, a widely studied near-infrared (NIR) active electrochromic dye. Apart from the well-defined dpi(Ru) --> pi(bpy)-based metal-to-ligand charge transfer (MLCT) transition bands at approximately 480 nm, this class of molecules generally shows another dpi(Ru) --> pi(Sq)(SOMO)-based intense MLCT band at around 900 nm, which is known to be redox active and bleaches reversibly upon a change in the oxidation state of the coordinated dioxolene moiety. To have better insight into the photoinduced electron transfer dynamics associated with this MLCT transition, detailed investigations have been carried out on exciting this MLCT band at 800 nm. Immediately after photoexcitation, bleach at 900 nm has been observed, whose recovery is...
The Journal of Physical Chemistry C, 2009
We have investigated the interfacial electron-transfer dynamics in ultrasmall TiO 2 nanoparticles... more We have investigated the interfacial electron-transfer dynamics in ultrasmall TiO 2 nanoparticles sensitized by alizarin using a femtosecond transient absorption technique. Electron injection has been confirmed by direct detection of the electron in the conduction band and cation radical of the adsorbed dye as monitored by transient absorption spectroscopy in the visible and near-IR region. The electron injection event was followed by monitoring the formation of the dye cation at 550 nm and also the conduction band electron at 900 nm, which revealed a multiexponential dynamics with time constants of 100 fs and 17 and 50 ps. This observation was explained on the basis of discreteness of the conduction band levels due to the finite size effect of the nanoparticle. The multiexponential injection indicated the event to be nonadiabatic contrary to debated literature reports. The back electron-transfer (BET) dynamics followed at the same wavelength revealed a fast component of value 0.2 ps and very slow BET time of >1 ns. The comparison with previous reports on bulk TiO 2 revealed a very slow BET in the present case which has been explained within the framework of Marcus theory. The result gives us direct proof of a nonadiabatic electron-transfer reaction in a strong binding dye like alizarin.
The Journal of Physical Chemistry C, 2010
We are reporting ultrafast charge carrier and charge transfer dynamics of the CdTe quantum dot (Q... more We are reporting ultrafast charge carrier and charge transfer dynamics of the CdTe quantum dot (QD) and type II CdTe/CdS core−shell QD materials with different shell (CdS) thicknesses. Herein, we have synthesized CdTe and CdTe/CdS core−shell quantum dots ...
Journal of Physical Chemistry C, 2008
We report synthesis of a new catechol derivative of 2,2′-bipyridyl (L 1 ) and two new Os(II)-poly... more We report synthesis of a new catechol derivative of 2,2′-bipyridyl (L 1 ) and two new Os(II)-polypyridyl complexes, I and II, with pendant catechol functionality (Scheme 1). Both complexes show two strong metalto-ligand charge transfer (MLCT) absorption bands in the visible region that are attributed to 1 MLCT (spin allowed) and 3 MLCT (spin forbidden) transitions. We have recorded photoluminescence spectra for both complexes at room temperature and at 77 K. We have determined the lifetime for the excited triplet ( 3 MLCT) states using time-resolved emission spectroscopy. Optical absorption studies reveal that both the complexes I and II form charge transfer (CT) complex with TiO 2 and ZrO 2 (higher band gap) nanoparticles. Photoinduced electron injection takes place from the Os(II)-complexes to the conduction band of TiO 2 and surface states of ZrO 2 nanoparticles following excitation of the respective CT complexes. On recombination of these respective charge-separated complexes, CT emission has been detected in the above dye/nanoparticle systems. Monitoring the CT emission, we could determine back electron transfer (BET) rate for the charge recombination process.
The Journal of Physical Chemistry C, 2009
... Kar , Sandeep Verma , Amitava Das* and Hirendra N. Ghosh* . Radiation and Photo Chemis... more ... Kar , Sandeep Verma , Amitava Das* and Hirendra N. Ghosh* . Radiation and Photo Chemistry Division, Bhabha Atomic Research Center, Mumbai, India, and Central Salt and Marine Chemicals Research Institute (CSIR), Bhavnagar 364002, Gujarat, India. J. Phys. Chem ...
The Journal of Physical Chemistry B, 2010
The aggregation behavior of 5,10,15-trisphenyl-20-(3,4-dihydroxy phenyl) porphyrin (L) in aqueous... more The aggregation behavior of 5,10,15-trisphenyl-20-(3,4-dihydroxy phenyl) porphyrin (L) in aqueous solution has been studied as a function of pH and concentration with the help of steady state absorption and emission spectroscopy. Our studies revealed that, for a particular concentration range, molecules of L undergo a reversible aggregation process and form two different aggregates at two different pH ranges, namely, J- and H-aggregates. We have monitored the excited state lifetimes of different aggregates by picosecond time-resolved emission spectroscopy and found that the emission lifetime of L reduces drastically with the formation of these aggregates. To study the dynamics associated with the excited state of both non-aggregated and aggregated (both J and H) porphyrins in an ultrafast time domain, we have carried out femtosecond transient absorption spectroscopy in the visible region following excitation of the respective samples at 400 nm. In addition to other de-excitation channels, another extra 100 fs (major) component for H-aggregates and 200 fs (major) component for J-aggregates has been observed and attributed to the exciton decay components of the respective aggregates.
The Journal of Physical Chemistry B, 2006
Interfacial electron transfer (ET) dynamics of 5,10,15-trisphenyl-20-(3,4-dihydroxybenzene) porph... more Interfacial electron transfer (ET) dynamics of 5,10,15-trisphenyl-20-(3,4-dihydroxybenzene) porphyrin (TPP-cat) adsorbed on TiO2 nanoparticles has been studied by femtosecond transient absorption spectroscopy in the visible and near-IR region exciting at 400 and 800 nm. TPP-cat molecule forms a charge transfer (CT) complex with TiO2 nanoparticles through the catechol moiety with the formation of a five-membered ring. Optical absorption measurements have shown that the Q-band of TPP-cat interacts strongly with TiO2 due to chelation; however, the Soret band is affected very little. Optical absorption measurements indicate that the catechol moiety also interacts with TiO2 nanoparticles showing the characteristic band of pure catechol-TiO2 charge transfer (CT) in the visible region. Electron injection has been confirmed by monitoring the cation radical, instant bleach, and injected electron in the conduction band of TiO2 nanoparticles. Electron injection time has been measured to be &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 100 fs and recombination kinetics has been best fitted with a multiexponential function, where the majority of the injected electrons come back to the parent cation radical with a time constant of approximately 800 fs for both excitation wavelengths. However, the reaction channel for the electron injection process has been found to be different for both wavelengths. Excitation at 800 nm, found to populate the CT state of the Q-band, and from the photoexcited CT state electron injection into the conduction band, takes place through diffusion. On the other hand, with excitation at 400 nm, a complicated reaction channel takes place. Excitation with 400 nm light excites both the CT band of Cat-TiO2 and also the Soret band of TPP-cat. We have discussed the reaction path in the TPP-cat/TiO2 system after exciting with both 400 and 800 nm laser light. We have also compared ET dynamics by exciting at both wavelengths.