Browsing by Author "Banerjee, Tanmay"

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Alkenes as Alkyne Equivalents in Radical Cascades Terminated by Fragmentations: Overcoming Stereoelectronic Restrictions on Ring Expansions for the Preparation of Expanded Polyaromatics
(ACS, 2015-04-23) Banerjee, Tanmay
Chemoselective interaction of aromatic enynes with Bu3Sn radicals can be harnessed for selective cascade transformations, yielding either Sn-substituted naphthalenes or Sn-indenes. Depending on the substitution at the alkene terminus, the initial regioselective 5-exo-trig cyclizations can be intercepted at the 5-exo stage via either hydrogen atom abstraction or C–S bond scission or allowed to proceed further to the formal 6-endo products via homoallylic ring expansion. Aromatization of the latter occurs via β-C–C bond scission, which is facilitated by 2c,3e through-bond interactions, a new stereoelectronic effect in radical chemistry. The combination of formal 6-endo-trig cyclization with stereoelectronically optimized fragmentation allows the use of alkenes as synthetic equivalents of alkynes and opens a convenient route to α-Sn-substituted naphthalenes, a unique launching platform for the preparation of extended polyaromatics.
Charge Delocalization in the Cascade Band Structure CdS/CdSe and CdS/CdTe Core–Shell Sensitized with Re(I)–Polypyridyl Complex
(ACS, 2016-04-21) Banerjee, Tanmay
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 (λpump = 400 nm, λprobe = 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.
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, Tanmay
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 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.
Diamine derivative of a ruthenium(II)-polypyridyl complex for chemodosimetric detection of nitrite ion in aqueous solution
(Elsiever, 2011-06-15) Banerjee, Tanmay
Nitrite 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.
Diphenylisobenzofuran Bound to Nanocrystalline Metal Oxides: Excimer Formation, Singlet Fission, Electron Injection, and Low Energy Sensitization
(ACS, 2018-11-20) Banerjee, Tanmay
We report the photophysical properties of the dicarboxylated diphenylisobenzofuran dye (1) bound to nanocrystalline metal oxide surfaces. With increased surface loading of 1, emission from the films is significantly quenched but with a small amount of excimer emission at maximum surface loadings. Long-lived triplets were observed by ns TA spectroscopy that are consistent with singlet fission occurring on mesoporous ZrO2. The evolution of these triplets, however, could not be convincingly resolved by our subnanosecond TA spectroscopy. Dye-sensitized devices composed of 1 on a TiO2|Al2O3 core–shell structure exhibited an unusual decrease, increase, and then decrease in Jsc with respect to the thickness of Al2O3. In these films the Al2O3 acts as a tunneling barrier to slow electron injection from the singlet excited state such that singlet fission, and electron injection from the triplet state becomes competitive. Proof-of-principle self-assembled bilayer films that exhibit efficient triplet energy transfer from a low energy absorbing dye to 1 is demonstrated as another step toward a SF-based DSSC that can circumvent the Shockley–Queisser limit.
Electronic, magnetic and photophysical properties of MOFs and COFs: general discussion
(RSC, 2017) Banerjee, Tanmay
Excited state proton transfer dye with an emission quantum yield up to 60% upon Zn2+ coordination
(Elsiever, 2021-06) Banerjee, Tanmay
Intramolecular excited state proton transfer (ESIPT) dyes are appealing for metal ion sensing because of their large apparent Stokes-shift, environmental sensitivity, and turn-on fluorescence capabilities. Here we introduce 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (2) as a new ESIPT sensing motif. The 2,5-bis(2-pyridylimino)pyrrole portion of 2 readily coordinates Hg2+, Zn2+, Co2+, Cu2+, and Ni2+ ions and results in a visible red-shift in absorption. While coordination of Hg2+, Co2+, Ni2+, and Cu2+ completely quenches emission, coordination to Zn2+ increases the ESIPT emission quantum yield from 25% to 60%. Unlike traditional ESIPT sensors, the metal ion binding site of 2 is intrinsic to the chromophore but is not the ESIPT site, thus enabling the selective modification of each functionality. As proof of concept, we use bromobutyrate as an alcohol protecting group whose cleavage by hydrazine results in turn-on fluorescence response. Collectively these results demonstrate the 1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole motif is sensitive to several stimuli (i.e. metal ion, base, solvent, and N2H4) and is a promising scaffolding for sensing applications.
H2 Evolution with Covalent Organic Framework Photocatalysts
(ACS, 2018-01-05) Banerjee, Tanmay
Covalent organic frameworks (COFs) are a new class of crystalline organic polymers that have garnered significant recent attention as highly promising H2 evolution photocatalysts. This Perspective discusses the advances in this field of energy research while highlighting the underlying peremptory factors for the rational design of readily tunable COF photoabsorber–cocatalyst systems for optimal photocatalytic performance.
Holey Heterographenes Made to Order: “Green” Synthesis of Porous Graphitic Frameworks
(Elsiever, 2020-04-09) Banerjee, Tanmay
Fully annulated pyrazine-linked porous graphitic frameworks (PGFs) have garnered attention because of their potential applications in optoelectronics and energy storage. In this issue of Chem, Zhang, Liu, and co-workers report a base-promoted aqueous synthesis of such porous heterographenes with high crystallinity and application potential as cathodes in lithium-ion batteries
Interfacial charge recombination of Os(ii)–polypyridyl–resorcinol complex on oleic acid capped TiO2 surface: what determines the dynamics?
(RSC, 2013) Banerjee, Tanmay
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.
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, Tanmay
Two 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.
Ionothermal Synthesis of Imide-Linked Covalent Organic Frameworks
(Wiley, 2020-06-23) Banerjee, Tanmay
Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time-consuming process and restricted to well-soluble precursor molecules. Synthesis of polyimide-linked COFs (PI-COFs) is further complicated by the poor reversibility of the ring-closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI-COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene-based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high-temperature XRPD analysis hints to the formation of precursor–salt adducts as crystalline intermediates, which then react with each other to form the COF.
Multimolecular assemblies on high surface area metal oxides and their role in interfacial energy and electron transfer
(RSC, 2018) Banerjee, Tanmay
High surface area metal oxides offer a unique substrate for the assembly of multiple molecular components at an interface. The choice of molecules, metal oxide, and the nature of the assembly method can have a profound influence on the mechanism, rate, and efficiency of photoinduced energy and electron transfer events at the interface. Owing to their diversity and high level of control, these interfacial assemblies are of interest for numerous applications including solar energy conversion, photoelectrosynthesis, photo-writable memory, and more. Although these assemblies are generated with very different goals in mind, they rely on similar surface binding motifs and molecular structure–property relationships. Therefore, the goal of this review is to summarize the various strategies (i.e. co-deposition, axial coordination, metal ion linkages, electrostatics, host–guest interactions, etc.) for assembling chromophores, hosts, electron donors/acceptors, and insulating co-adsorbent molecules on mesoporous metal oxide substrates. The assembly, synthesis, and characterization, as well as subsequent photoinduced events (i.e. cross-surface energy/electron transfer, interchromophore energy transfer, electron injection, and others) are discussed for the various assembly strategies.
A new receptor with a FRET based fluorescence response for selective recognition of fumaric and maleic acids in aqueous medium
(RSC, 2013) Banerjee, Tanmay
Preferential 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 medium
New Ru(ii)/Os(ii)-polypyridyl complexes for coupling to TiO2 surfaces through acetylacetone functionality and studies on interfacial electron-transfer dynamics
(RSC, 2014) Banerjee, Tanmay
New Ru(II)- and Os(II)-polypyridyl complexes have been synthesized with pendant acetylacetone (acac) functionality for anchoring on nanoparticulate TiO2 surfaces with a goal of developing an alternate sensitizer that could be utilized for designing an efficient dye-sensitized solar cell (DSSC). Time-resolved transient absorption spectroscopic studies in the femtosecond time domain have been carried out. The charge recombination rates are observed to be very slow, compared with those for strongly coupled dye molecules having catechol as the anchoring functionality. The results of such studies reveal that electron-injection rates from the metal complex-based LUMO to the conduction band of TiO2 are faster than one would expect for an analogous complex in which the chromophoric core and the anchoring moiety are separated with multiple saturated C–C linkages. Such an observation is rationalized based on computational studies, and a relatively smaller spatial distance between the dye LUMO and the TiO2 surface accounted for this. Results of this study are compared with those for analogous complexes having a gem-dicarboxy group as the anchoring functionality for covalent binding to the TiO2 surface to compare the role of binding functionalities on electron-transfer dynamics.
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, Tanmay
Femtosecond 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.
Nonlinear Optical Switching in Regioregular Porphyrin Covalent Organic Frameworks
(Wiley, 2019-03-12) Banerjee, Tanmay
Covalent organic frameworks (COFs) have garnered immense scientific interest among porous materials because of their structural tunability and diverse properties. However, the response of such materials toward laser-induced nonlinear optical (NLO) applications is hardly understood and demands prompt attention. Three novel regioregular porphyrin (Por)-based porous COFs—Por-COF-HH and its dual metalated congeners Por-COF-ZnCu and Por-COF-ZnNi—have been prepared and present excellent NLO properties. Notably, intensity-dependent NLO switching behavior was observed for these Por-COFs, which is highly desirable for optical switching and optical limiting devices. Moreover, the efficient π-conjugation and charge-transfer transition in ZnCu-Por-COF enabled a high nonlinear absorption coefficient (β=4470 cm/GW) and figure of merit (FOM=σ1/σo, 3565) value compared to other state-of-the-art materials, including molecular porphyrins (β≈100–400 cm/GW), metal–organic frameworks (MOFs; β≈0.3–0.5 cm/GW), and graphene (β=900 cm/GW).
Photon Upconversion and Photocurrent Generation via Self-Assembly at Organic–Inorganic Interfaces
(ACS, 2015-10-22) Banerjee, Tanmay
Molecular photon upconversion via triplet–triplet annihilation (TTA-UC), combining two or more low energy photons to generate a higher energy excited state, is an intriguing strategy to surpass the maximum efficiency for a single junction solar cell (<34%). Here, we introduce self-assembled bilayers on metal oxide surfaces as a strategy to facilitate TTA-UC emission and demonstrate direct charge separation of the upconverted state. A 3-fold enhancement in transient photocurrent is achieved at light intensities as low as two equivalent suns. This strategy is simple, modular and offers unprecedented geometric and spatial control of the donor–acceptor interactions at an interface. These results are a key stepping stone toward the realization of an efficient TTA-UC solar cell that can circumvent the Shockley–Queisser limit.
Photosensitization of nanoparticulate TiO2 using a Re(i)-polypyridyl complex: studies on interfacial electron transfer in the ultrafast time domain
(RSC, 2012) Banerjee, Tanmay
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˙
Polymer photocatalysts for solar-to-chemical energy conversion
(Nature, 2020-11-05) Banerjee, Tanmay
Solar-to-chemical energy conversion for the generation of high-energy chemicals is one of the most viable solutions to the quest for sustainable energy resources. Although long dominated by inorganic semiconductors, organic polymeric photocatalysts offer the advantage of a broad, molecular-level design space of their optoelectronic and surface catalytic properties, owing to their molecularly precise backbone. In this Review, we discuss the fundamental concepts of polymeric photocatalysis and examine different polymeric photocatalysts, including carbon nitrides, conjugated polymers, covalent triazine frameworks and covalent organic frameworks. We analyse the photophysical and physico-chemical concepts that govern the photocatalytic performance of these materials, and derive design principles and possible future research directions in this emerging field of ‘soft photocatalysis’.