@article {42538, title = {Competitive binding of Ba2+and Sr2+ to 18-crown-6 in a receptor with a 1-methoxyanthraquinone analogue as the other binding site}, journal = {Europian Journal of Inorganic Chemistry}, year = {2011}, month = {OCT}, pages = {4680{\textendash}4690}, abstract = {

Owing to their immense biological significance, development of sensors for the selective detection of alkaline earth metal ions has attracted vast research interest. In this article we have reported the synthesis, characterisation and ion binding studies of a new RuII-polypyridyl-crown-anthraquinone complex (5). Studies confirm selective binding of BaII, SrII and CaII ions, with Kmath image \> Kmath image \>\> Kmath image, over all other metal ions, to the crown ether moiety and not to the methoxy anthraquinone component, the latter being the second binding site available and known for its affinity towards alkaline earth metal ions from one of our previous reports.

}, doi = {10.1002/ejic.201100472}, author = {Banerjee, Tanmay and Suresh, Moorthy and Ghosh, Hirendra N. and Das, Amitava} } @article {42516, title = {Photosensitization of nanoparticulate TiO2 using a Re(I)-polypyridyl complex: studies on interfacial electron transfer in the ultrafast time domain}, journal = {Physical Chemistry Chemical Physics}, volume = {14}, year = {2012}, month = {APR}, pages = {8192-8198}, abstract = {

We have synthesized a new photoactive rhenium(I)-complex having a pendant catechol functionality [Re(CO)3Cl(L)] (1) (L is 4-[2-(4'-methyl-2,2'-bipyridinyl-4-yl)vinyl]benzene-1,2-diol) for studying the dynamics of the interfacial electron transfer between nanoparticulate TiO2 and the photoexcited states of this Re(I)-complex using femtosecond transient absorption spectroscopy. Our steady state absorption studies revealed that complex 1 can bind strongly to TiO2 surfaces through the catechol functionality with the formation of a charge transfer (CT) complex, which has been confirmed by the appearance of a new red-shifted CT band. The longer wavelength absorption band for 1, bound to TiO2 through the proposed catecholate functionality, could also be explained based on the DFT calculations. Dynamics of the interfacial electron transfer between 1 and TiO2 nanoparticles was investigated by studying kinetics at various wavelengths in the visible and near infrared regions. Electron injection into the conduction band of the nanoparticulate TiO2 was confirmed by detection of the conduction band electron in TiO2 (Image ID:c2cp24105f-t1.gif) and the cation radical of the adsorbed dye (1˙+) in real time as monitored by transient absorption spectroscopy. A single exponential and pulse-width limited (\<100 fs) electron injection was observed. Back electron transfer dynamics was determined by monitoring the decay kinetics of 1˙+ and Image ID:c2cp24105f-t2.gif.

}, doi = {10.1039/C2CP24105F}, author = {Kar, Prasenjit and Banerjee, Tanmay and Verma, Sandeep and Sen, Anik and Das, Amitava and Ganguly, Bishwajit and Ghosh, Hirendra N.} } @article {42510, title = {Sequential energy and electron transfer in polynuclear complex sensitized TiO2 nanoparticles}, journal = {Journal of Physical Chemistry Letters}, volume = {3}, year = {2012}, month = {MAY}, pages = {1543{\textendash}1548}, abstract = {

Polynuclear{\textendash}polypyridyl complexes exhibit a directional energy-transfer property that can improve their photosensitization activity. In the present work, the energy-transfer process is explored in a trinuclear Ru2∧Os1 complex using transient absorption spectroscopy. This study reveals an efficient excitation energy transfer from the terminal (RuII complex) to the core (OsII complex) region in the ultrafast time domain (400 fs{\textendash}40 ps). The excitation energy funnel is useful in improving the functionalized core activity. This is evidenced in an interfacial electron-transfer study of Ru2∧Os1, Ru2∧Ru1, and Os1 complex sensitized TiO2 nanoparticle (TiO2 NP) systems. The intramolecular energy transfer causes sequential excitation of the core part of the Ru2∧Os1 complex, which leads to multiexponential electron injection into TiO2 NP. Besides this, the electronic coupling between the metal ion centers stabilizes the positive charge within the trinuclear complex, which results in a slow charge recombination reaction. This study shows that polynuclear complexes can be very useful for their panchromatic effects, unidirectional energy- and electron-transfer properties.

}, doi = {10.1021/jz3005305}, author = {Verma, Sandeep and Kar, Prasenjit and Banerjee, Tanmay and Das, Amitava and Ghosh, Hirendra N.} } @article { ISI:000324758700022, title = {Interfacial charge recombination of Os(II)-polypyridyl-resorcinol complex on oleic acid capped TiO2 surface: what determines the dynamics?}, journal = {New Journal of Chemistry}, volume = {37}, number = {10}, year = {2013}, month = {JUL}, pages = {3100-3108}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Femtosecond transient absorption spectroscopic studies of an osmium(II)-polypyridyl-resorcinol complex, 1, on oleic acid capped TiO2 have been carried out and the results have been compared with our previous studies on poly(vinyl) alcohol capped TiO2. While on both these surfaces the complex exhibits a single exponential \<120 fs injection, the back electron transfer reaction is slower on the oleic acid capped TiO2 surface early on while it is faster on the same surface at longer times than on poly(vinyl)alcohol capped TiO2. The probable origin of these disparate observations has been analyzed.

}, issn = {1144-0546}, doi = {10.1039/c3nj00550j}, author = {Banerjee, Tanmay and Das, Amitava and Ghosh, Hirendra N.} } @article { ISI:000346321700065, title = {Size quantization effects on interfacial electron transfer dynamics in Ru(II)-polypyridyl complex sensitized ZnO QDs}, journal = {Journal of Physical Chemistry C}, volume = {118}, number = {49}, year = {2014}, month = {DEC}, pages = {28898-28905}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Quantum-size confinement in semiconductor material offers size based tunability of interband gap energy as well as intraband sublevels. In this work, size quantization of wide bandgap ZnO quantum dots has been explored in the study of interfacial charge separation reaction using a catechol functionalized Ru(II)polypyridyl complex as a photosensitizer molecule. Femtosecond time-resolved transient absorption studies have revealed multiple electron injection events based on discrete conduction band states of ZnO QDs. The electron injection rates have been rationalized for quantum confinement effects owing to different sizes of ZnO QDs. Furthermore, the size dependency of the intrinsic lifetime of electrons injected into discrete energy levels of ZnO QDs has been revealed in charge recombination reaction with the Ru(III)polypyridyl complex cation. The charge recombination dynamics reveals a competing trend of carrier confinement and carrier leak upon reducing particle size. This study shows the optimization of finite size effects in achieving better interfacial charge separation at the dye/semiconductor interface.

}, issn = {1932-7447}, doi = {10.1021/jp5101158}, author = {Verma, Sandeep and Das, Amitava and Ghosh, Hirendra N.} } @article { ISI:000366006300012, title = {Hydrogen bond and ligand dissociation dynamics in fluoride sensing of Re(I)-polypyridyl complex}, journal = {Journal of Physical Chemistry B}, volume = {119}, number = {47}, year = {2015}, month = {NOV}, pages = {14952-14958}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Hydrogen bonding interaction plays an essential role in the early phases of molecular recognition and colorimetric sensing of various anions in aprotic media. In this work, the host-guest interaction between fac-[Re(CO)(3)Cl(L)] with L = 4-([2,2{\textquoteright}-bipyridin]-4-yl)phenol and fluoride ions is investigated for the hydrogen bond dynamics and the changing local coordination environment. The stoichiometric studies using H-1 NMR and ESI-MS spectroscopies have shown that proton transfer in the H-bonded phenol-fluoride complex activates the dissociation of the CO ligand in the Re(I) center. The phenol-to-phenolate conversion during formation of HF2- ion induces nucleophilic lability of the CO ligand which is probed by intraligand charge transfer (ILCT) and ligand-to-metal charge transfer (LMCT) transitions in transient absorption spectroscopy. After photoexcitation, phenol-phenoxide conversion rapidly equilibrates in 280 fs time scale and the ensuing excited state [ReII(bpy(center dot-)-phenolate(-))(CO)(3)Cl]* undergoes CO dissociation in the ultrafast time scale of similar to 3 ps. A concerted mechanism of hydrogen cleavage and coordination change is established in anion sensing studies of the rhenium complex.

}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.5b09227}, author = {Verma, Sandeep and Aute, Sunil and Das, Amitava and Ghosh, Hirendra N.} } @article { ISI:000349942400010, title = {Ultrafast electron injection, hole transfer, and charge recombination dynamics in cdse QD super-sensitized Re(I)-polypyridyl complexes with catechol and resorcinol moiety: effect of coupling}, journal = {Journal of Physical Chemistry C}, volume = {119}, number = {7}, year = {2015}, month = {FEB}, pages = {3522-3529}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Ultrafast charge-transfer dynamics have 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. The energy level diagram of CdSe QD and Re1,2 and Re1,3 sensitizer reveals that photoexcited 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 photoexcitation. Femtosecond transient absorption studies have been carried out to monitor charge-transfer dynamics in early time scale. Transient absorption spectra show formation of cation radicals for both Re1,2 and Re1,3 in the 550-650 nm region with a peak at 590 nm region and broad absorption in the 650-1000 nm region, which can be attributed to photoexcited electron in the conduction band of CdSe QD. Charge recombination was determined by monitoring the decay of cation radicals as well as decay of an electron and found to be slower in the Re1,3/CdSe system as compared to that of the Re1,2/CdSe system, which is due to weaker electronic coupling in the former system.

}, issn = {1932-7447}, doi = {10.1021/jp5122068}, author = {Debnath, Tushar and Maity, Partha and Banerjee, Tanmay and Das, Amitava and Ghosh, Hirendra N.} } @article { ISI:000375969000056, title = {Charge delocalization in the cascade band structure CdS/CdSe and CdS/CdTe core-shell sensitized with Re(I)-polypyridyl complex}, journal = {Journal of Physical Chemistry C}, volume = {120}, number = {18}, year = {2016}, month = {MAY}, pages = {10051-10061}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

Charge-carrier dynamics of CdS quantum dot (QD) and CdS/CdSe type-I and CdS/CdTe type-II core shell nanocrystals (NCs) sensitized with a Re(I)-polypyridyl complex have been carried with special emphasis on studies on carrier delocalization and the role of Re-complex as a hole acceptor and sensitizer molecule. Our investigation confirmed photoexcited hole transfer from CdS and CdS/CdSe to the Re-complex, while no hole transfer was observed in the CdS/CdTe Re-complex system. This was rationalized by the evaluation of the relative energy levels, which revealed that such hole migration was not energetically favorable due to low-lying highest occupied molecular orbital (HOMO) of the Re-complex as compared with the valence band (VB) of CdTe shell; however, luminescence quenching from upper excited states of Re-complex was observed in the presence of all three QD and core shell systems, which has been attributed to electron injection from hot state (energetically higher than the LUMO state) of the Re-complex to the conduction band (CB) of the QDs. Transient absorption (lambda(pump) = 400 nm, lambda(probe) = 450-750 nm) spectra recorded for Re complex-sensitized CdS and CdS/CdSe composite in the femtosecond time domain revealed a broad transient absorption band in the 580-750 nm region with a peak around 595 nm, and this was attributed to the cation radical formation for Re-complex, either by capturing photoexcited hole from the NCs or by injecting electron to the CB of the NCs. As anticipated, no such spectrum was observed for the CdS/CdTe Re-complex composite system after 400 nm excitation. Electron injection from photoexcited Re-complex to CdS QD and CdS/CdSe core shell was found to be \<100 fs, while the hole transfer from photoexcited CdS QD and CdS/CdSe core shell to Re-complex took place within the time scale of 900 fs and 2.5 ps, respectively.

}, issn = {1932-7447}, doi = {10.1021/acs.jpcc.6b01654}, author = {Maity, Partha and Debnath, Tushar and Banerjee, Tanmay and Das, Amitava and Ghosh, Hirendra N.} } @article {43452, title = {Proton-coupled electron transfer in a hydrogen-bonded charge transfer complex}, journal = {Journal of Physical Chemistry B}, volume = {120}, year = {2016}, month = {OCT}, pages = {10780-10785}, abstract = {A proton-coupled electron transfer (PCET) reaction in a hydrogen bonded charge-transfer (CT) complex of 4-([2,2{\textquoteright}-bipyridin]-4-yl)phenol (bpy-phenol) with a F- ion has been investigated by ultrafast time-resolved transient absorption spectroscopy. The phenolic receptor molecule, bpy-phenol, binds to the F- ion through a hydrogen bond and senses the F- ion-via the Stokes-shifted CT band. Upon photoexcitation, CT from the phenol residue to the bpy residue promotes proton transfer from the phenol radical cation (ArOH center dot+) to the fluoride ion at ultrafast time scales of <150 fs (instrument response function limited) and 3 ps, separately. The fast and slow proton-transfer times are linked to two different types of hydrogen-bonding networks between the phenol residue and fluoride ion. Crystalline water in the fluoride salt hydrates mediates the proton-transfer reaction. This work demonstrates the participation of a hydrogen-bonded water bridge within a PCET reaction in a water restricted environment.}, doi = {10.1021/acs.jpcb.6b06032}, author = {Verma, Sandeep and Aute, Sunil and Das, Amitava and Ghosh, Hirendra N.} } @article {43955, title = {Demonstrating the role of anchoring functionality in interfacial electron transfer dynamics in newly synthesized BODIPY-TiO2 nanostructure composite}, journal = {New Journal of Chemistry}, volume = {41}, year = {2017}, month = {MAY}, type = {Article}, abstract = {New Bodipy derivatives (Dye 1 and 2) having catechol or resorcinol functionality for anchoring to the nanostructured (NS) TiO2 surfaces have been synthesized. Extended conjugation at one of the two pyrrole rings at the C3 position has helped us in achieving the desired control in tuning the optical and redox properties of the BODIPY based dye molecules. Relative emission quantum yields (em1 = ~52 {\textpm} 2\% and em2 = 54 {\textpm} 2\%) are found to be much higher in polar aprotic solvent (acetonitrile), while this are found to be substantially lower for dye 1 in polar protic solvent. Steady state optical absorption studies reveal the formation of a strong charge transfer complex between dye 1 and NS-TiO2, while this interaction is much weaker for dye 2. Transient absorption studies have been carried out for 1/NS-TiO2 and 2/NS-TiO2 systems following excitation with a laser source of 400 nm for understanding the charge transfer dynamics. Results of the transient absorption spectral studies helped in elucidating role of anchoring functionality in influencing the dynamics of the interfacial electron transfer and the charge recombination process in ultrafast time scale.}, doi = {10.1039/C7NJ00668C}, author = {Ghosh, Hirendra N. and Das, Amitava and Aute, Sunil and Maity, Partha} } @article {43550, title = {Proton-coupled electron-transfer processes in ultrafast time domain: evidence for effects of hydrogen-bond stabilization on photoinduced electron transfer}, journal = {Chemistry-A European Journal}, volume = {23}, year = {2017}, month = {MAR}, pages = {3455-3465}, abstract = {The proton-coupled electron-transfer (PCET) reaction is investigated for a newly synthesized imidazoleanthraquinone biomimetic model with a photoactive RuIIpolypyridyl moiety that is covalently coupled to the imidazole fragment. Intramolecular H-bonding interactions between imidazole and anthraquinone moieties favor the PCET process; this can be correlated to an appreciable positive shift in the one-electron reduction potential of the coordinated anthraquinone moiety functionalized with the imidazole fragment. This can also be attributed to the low luminescence quantum yield of the RuII-polypyridyl complex used. The dynamics of the intramolecular electron-transfer (ET) and PCET processes are studied by using femtosecond transient absorption spectroscopy. The steady- state spectroscopic studies and the results of the time- resolved absorption studies confirm that H- bonded water molecules play a major role in both ET and PCET dynamics as a proton relay in the excited state. The electron- transfer process is followed by a change in the H- bonding equilibrium between AQ and imidazole in acetonitrile solvent, and protonation of AQ(-) water leads to PCET in the presence of water. A slower forward and backward electron- transfer rate is observed in the presence of D2O compared with that in H2O. These results provide further experimental support for a detailed understanding of the PCET process.}, doi = {10.1002/chem.201605594}, author = {Dey, Ananta and Dana, Jayanta and Aute, Sunil and Maity, Partha and Das, Amitava and Ghosh, Hirendra N.} } @article {46341, title = {Hydrogen bond assisted photoinduced intramolecular electron transfer and proton coupled electron transfer in an ultrafast time domain using a ruthenium-anthraquinone dyad}, journal = {Photochemical \& Photobiological Sciences}, volume = {18}, year = {2019}, month = {OCT }, pages = {2430-2441}, type = {Article}, abstract = {

Quinones play a significant role as primary electron acceptors in the natural photosynthetic system of photosystem II, and their reduction is known to be facilitated by hydrogen-bond donors or protonation. In this study, a ruthenium(ii) polypyridyl complex 1 coupled to an anthraquinone (AQ) functionality through a rigid imidazole (Im) spacer has been synthesized to examine the effect of H-bonding on both the thermal and photoinduced electron transfer reactions. The anthraquinone moiety of complex 1 is fused to a benzi-imidazole system bearing C \& xe001;(OMIDLINE)-M-AQ HORIZONTAL ELLIPSISHNIm based H-bonding at one side of the anthraquinone moiety so that intramolecular hydrogen bonding from the imidazole group to the nearby quinone carbonyl can occur. The hydrogen bond formation involving the semiquinone radical anion produced through the photoinduced reduction process in Ru-im-AQ and the imidazole proton in complex 1 resulted in a significant positive shift of one electron reduction potential of complex 1. The kinetics for the formation of the charge-separated states was explored by using femtosecond transient absorption spectroscopy. Hydrogen bonding between water and the reduced anthraquinone accounted for thermodynamic and kinetic stabilization of these charge-separated states. An attempt has been made to assess the relative importance of the driving force and solvent polarity, in the rates of photoinduced electron transfer in complex 1. The 490 nm transient absorption band of anthraquinone radical anions (AQ(-)) and a broad absorption in the 580-750 nm region having maxima at similar to 690 nm have been observed and this is attributed to the generation of a transient Ru3+-species of the corresponding complex 1. Addition of water entails an acceleration of electron transfer rates by a factor of 3.33. The system investigated may serve as a model for the mechanistic diversity of PCET reactions in general with water as a primary proton donor. Furthermore, our studies are relevant for understanding proton-coupled electron transfer (PCET) reactivity of electronically excited states at a fundamental level because changes in hydrogen-bonding strength accompanying changes in redox states may be regarded as a variant form of PCET.

}, issn = {1474-905X}, doi = {10.1039/c9pp00135b}, author = {Dey, Ananta and Dana, Jayanta and Aute, Sunil and Das, Amitava and Ghosh, Hirendra N.} } @article {48771, title = {Donor strapped perylene bisimide macrocycle and its lemniscate dimer with extended charge separation}, journal = {Inorganic Chemistry Frontiers}, volume = {10}, year = {2023}, month = {OCT }, pages = {5099-5107}, type = {Article}, abstract = {

Macrocyclic structures are fascinating due to their unique design and capability to place chromophores in specific orientations, resulting in exciting optoelectronic properties. However, the synthetic challenges limit the broad exploration of such systems. Herein, we report a thiophene-diacetylene-based ring strapped perylene bisimide macrocycle and its notably different electron transfer features. Single-crystal analysis of the macrocycle pointed to the nearly orthogonal placement of donor-acceptor units, facilitating better electronic communication between them. Interestingly, introduction of an alkyl substituent on the peripheral thiophene ring opened the possibility of forming a higher oligomer macrocycle consisting of two strapped perylene bisimide units. Diffusion and two-dimensional NMR experiments provided insight into the structure of the figure-eight-shaped lemniscate dimer. Transient absorption measurements showed faster electron transfer and extended stabilization of the charge-separated state. The thiophene-diacetylene-based ring is a better donor unit to facilitate rapid electron transfer and extended charge separation in the macrocycle and its lemniscate dimer. The new macrocycle design enables the formation of higher analogs equally capable of stabilizing the charge-separated state. Donor-acceptor (D-A) macrocycle designs position the respective units to achieve ultrafast electron transfer precisely and an extended charge-separated state. Here, we report a D-A macrocycle and its lemniscate dimer molecule with exciting electron transfer features.

}, issn = {2052-4129}, doi = {10.1039/d3qo01060k}, author = {Veer, Sairam Dnyaneshwar and Goswami, Tanmay and Ravindranathan, Sapna and Gonnade, Rajesh and Kharbanda, Nitika and Ghosh, Hirendra N. and Babu, Sukumaran Santhosh} } @article {48451, title = {Oligothiophene-ring-strapped perylene bisimides: functionalizable coaxial donor-acceptor macrocycles}, journal = {Angewandte Chemie-International Edition}, volume = {62}, year = {2023}, month = {JAN}, type = {Article}, abstract = {

Aesthetic designs from nature enable new knowledge to be gained and, at the same time, inspire scientific models. In this context, multicomponent macrocycles embody the advantage of precisely positioning the structural units to achieve efficient communication between them. However, the construction of a functionalizable macrocycle for ultrafast charge separation and stabilization has not been attempted. Herein, we report the synthesis, crystal structure, and transient absorption of a new functionalizable macrocycle consisting of an oligothiophene-ring-strapped perylene bisimide. Transient absorption results point to a sequential improvement in charge separation and stabilization from the macrocycle to the corresponding linear dimer and 2D polymer due to the unique design. Our macrocycle design with a supportive spatial arrangement of the donor and acceptor units will inspire the development of more complex synthetic systems with exciting electron-transfer and charge-separation features.

}, keywords = {Charge Separation, Donor-Acceptor Systems, Electron Transfer, Macrocycles, Perylene Bisimides}, issn = {1433-7851}, doi = {10.1002/anie.202212934}, author = {Dnyaneshwar Veer, Sairam and Chandrakant Wakchaure, Vivek and Asokan, Kiran and Dixit, Ruchi and Goswami, Tanmay and Saha, Ramchandra and Gonnade, Rajesh and Ghosh, Hirendra N. and Santhosh Babu, Sukumaran} }