BITS Faculty Publications
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Item Urea/thiourea derivatives and Zn(II)-DPA complex as receptors for anionic recognition—A brief account(IAS, 2011-03) Banerjee, TanmayThis review covers few examples of anion complexation chemistry, with a special focus on urea/thiourea-based receptors and Zn(II)-dipicolyl amine-based receptors. This article specially focuses on structural aspects of the receptors and the anions for obtaining the desire specificity along with an efficient receptor–anion interaction. Two types of receptors have been described in this brief account; first one being the strong hydrogen bond donor urea/thiourea derivatives, which binds the anionic analytes through hydrogen bonded interactions; while, the second type of receptors are coordination complexes, where the coordination of the anion to the metal centre. In both the cases the anion binding modulate the energy gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) and thereby the spectroscopic response. Appropriate choice of the signalling unit may allow probing the anion binding phenomena through visual detection.Item Diamine derivative of a ruthenium(II)-polypyridyl complex for chemodosimetric detection of nitrite ion in aqueous solution(Elsiever, 2011-06-15) Banerjee, TanmayNitrite is quite an abundant anion in the environment. It, however, becomes toxic to human life, as well as aquatic animals when present above the permissible concentration level. We have reported here a Ru(II)-polypyridyl-based complex (1) for chemodosimetric detection of nitrite ion in aqueous solution. Formation of the new triazole based complex, generated by reaction of 1 and N2O3, is ascertained by comparing its properties with a presynthesised triazole complex.Item Interfacial Electron Transfer Dynamics of Two Newly Synthesized Catecholate Bound RuII Polypyridyl-Based Sensitizers on TiO2 Nanoparticle Surface – A Femtosecond Pump Probe Spectroscopic Study(Wiley, 2011-08-17) Banerjee, TanmayTwo new catecholate-bound RuII–polypyridine based sensitizers, (2,2′-bipyridine){ethyl 3-(4-hydroxyphenyl)-2-[(4′-methyl-2,2′-bipyridinyl-4-carbonyl)amino]propionate}{4-[2-(4′-methyl-2,2′-bipyridinyl-4-yl)vinyl]benzene-1,2-diol)}ruthenium(II) hexafluorophosphate (5) and [(2,2′-bipyridine)-(4-2,2′-bipyridinyl-4-yl-phenol)-(4-{2-(4′-methyl-2,2′-bipyridinyl-4-yl)vinyl}benzene-1,2-diol)]ruthenium(II) hexafluorophosphate (6) with secondary electron-donating groups (tyrosine and phenol, respectively) were synthesized and characterized. Steady-state optical absorption and emission studies confirm strong coupling between the sensitizers and TiO2 nanoparticles. Femtosecond visible transient absorption spectroscopy has been employed to study interfacial electron transfer (IET) dynamics in the dye–nanoparticle systems to explore the influence of the secondary electron-donating groups on IET dynamics. Electron injection into the conduction band of nanoparticulate TiO2 has been confirmed by detection of the conduction band electrons in TiO2 ([e–]TiO2CB) and radical cation of the adsorbed dye (D·+) in real time monitored by transient absorption spectroscopy. A single exponential and pulse-width limited (< 100 fs) electron injection has been observed. Back electron transfer (BET) dynamics have been studied by monitoring the decay kinetics of the injected electron in the conduction band of TiO2 and by the recovery of the ground state bleach. BET dynamics in dye–TiO2 systems for complexes 5 and 6 have been compared with those of [bis(2,2′-bpy)-(4-{2-(4′-methyl-2,2′-bipyridinyl-4-yl)vinyl}benzene-1,2-diol)]ruthenium(II) hexafluorophosphate (7), which does not have a secondary electron-donating group.Item Competitive binding of Ba2+and Sr2+ to 18-Crown-6 in a Receptor with a 1-Methoxyanthraquinone Analogue as the Other Binding Site(Wiley, 2011-09-06) Banerjee, TanmayOwing 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 Kurn:x-wiley:14341948:media:EJIC201100472:tex2gif-inf-1 > Kurn:x-wiley:14341948:media:EJIC201100472:tex2gif-inf-2 >> Kurn:x-wiley:14341948:media:EJIC201100472:tex2gif-inf-3, 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.Item Sequential Energy and Electron Transfer in Polynuclear Complex Sensitized TiO2 Nanoparticles(ACS, 2012-05-19) Banerjee, TanmayPolynuclear–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–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.Item Photosensitization of nanoparticulate TiO2 using a Re(i)-polypyridyl complex: studies on interfacial electron transfer in the ultrafast time domain(RSC, 2012) Banerjee, TanmayWe 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˙Item A new receptor with a FRET based fluorescence response for selective recognition of fumaric and maleic acids in aqueous medium(RSC, 2013) Banerjee, TanmayPreferential binding of a new reagent to fumaric acid could be utilized for its estimation in aqueous medium and in commercial fruit juice.Molecular recognition studies of dicarboxylic acids have gained importance because of their presence as key structural moieties in many bioactive molecules, their role in various metabolic processes and involvement in the biosynthesis of some important intermediates.1 Fumaric (Fum) and maleic (Mal) acids find a broad range of uses in medicine, food and polymer industries.1 More recently, fumaric acid derivatives have been tested for treatment of multiple sclerosis and patients with psoriasis.2 Maleic acid is known for its role as an inhibitor of the Krebs cycle and in different kidney diseases.2 Due to the widespread use of these two acids as ingredients in food as well as beverages and their possible adverse influences on human health upon prolonged exposure, it is important to develop an efficient reagent for their recognition and quantitative estimation in aqueous mediumItem Newly Designed Resorcinolate Binding for Ru(II)– and Re(I)–Polypyridyl Complexes on Oleic Acid Capped TiO2 in Nonaqueous Solvent: Prolonged Charge Separation and Substantial Thermalized 3MLCT Injection(ACS, 2013-01-23) Banerjee, TanmayFemtosecond pump–probe spectroscopic studies on a series of newly synthesized resorcinol-based Ru(II) and Re(I) complexes on oleic acid capped TiO2 nanoparticles have been carried out in chloroform, and the results are compared with those of the catechol analogues. The ruthenium complex shows biexponential injection; the second component arises due to injection from the thermally equilibrated 3MLCT states as a result of a weaker strength of the resorcinolate binding. Also, in comparison with catechol binding, as a result of a greater diffusion of the injected electrons into TiO2, the back electron transfer (BET) is slowed down significantly for the ruthenium complex. These are distinctive observations for any mononuclear ruthenium–polypyridyl–enediol complex reported thus far. However, the rhenium complex educes single exponential ultrafast injection (<120 fs) because of apparent injection in a high density of states and shows the most prominent results with ∼50% slowdown in the charge recombination rate as compared to the analogous catechol bound system. These results exemplify the probable development of highly capable sensitizer dyes with resorcinol as the anchoring group for the development of efficient dye-sensitized solar cells.Item Synthesis, Steady-State, and Femtosecond Transient Absorption Studies of Resorcinol Bound Ruthenium(II)- and Osmium(II)-polypyridyl Complexes on Nano-TiO2 Surface in Water(ACS, 2013-04-05) Banerjee, TanmayThe synthesis of two new ruthenium(II)- and osmium(II)-polypyridyl complexes 3 and 4, respectively, with resorcinol as the enediol anchoring moiety, is described. Steady-state photochemical and electrochemical studies of the two sensitizer dyes confirm strong binding of the dyes to TiO2 in water. Femtosecond transient absorption studies have been carried out on the dye–TiO2 systems in water to reveal <120 fs and 1.5 ps electron injection times along with 30% slower back electron transfer time for the ruthenium complex 3. However, the corresponding osmium complex 4 shows strikingly different behavior for which only a <120 fs ultrafast injection is observed. Most remarkably, the back electron transfer is faster as compared to the corresponding catechol analogue of the dye. The origin and the consequences of such profound effects on the ultrafast interfacial dynamics are discussed. This Article on the electron transfer dynamics of the aforesaid systems reinforces the possibility of resorcinol being explored and developed as an extremely efficient binding moiety for use in dye-sensitized solar cells.Item Interfacial charge recombination of Os(ii)–polypyridyl–resorcinol complex on oleic acid capped TiO2 surface: what determines the dynamics?(RSC, 2013) Banerjee, TanmayFemtosecond 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.