Aggregation-Induced Modulation of Ground and Excited State Photophysics of 5-(tert-Butyl)-2-Hydroxy-1,3-Isophthalaldehyde (5-tBHI) Aparna Shukla, Abhipsa Sekhar Biswal, Arkaprava Chowdhury, Ritaban Halder, and Soumit Chatterjee American Chemical Society (ACS) 5-(tert-Butyl)-2-hydroxy-1,3-isophthalaldehyde (5-tBHI) is a photochromic material susceptible to either excited state proton transfer or excited state intramolecular proton transfer, depending upon the solvent. However, it has also been found to aggregate in the presence of sodium dodecyl sulfate. In this current study, based on the steady-state and time-resolved spectroscopy, supported by crystallography, quantum chemical density functional theory calculation, and molecular dynamics (MD) simulation, we report on the aggregation of this potential single benzene-based emitter (SBBE) in neat solvents as well as solid phase to modulate its photophysics. It has been found that 5-tBHI forms mixed aggregates of different orders, owing to the presence of both enolic and tautomeric forms, to yield tunable emission, although the emission intensity is quenched. These findings suggest that the intramolecular hydrogen bonding of 5-tBHI not only limits intermolecular interactions but also promotes nonradiative deactivation pathways. Hence, designing and structural engineering, with a focus to suppressing intramolecular hydrogen bonding as well as increasing through space conjugation by replacing the aldehydic moieties with bulky aliphatic or aromatic ketonic groups, can be a plausible approach to yielding improved probes with tunable emission and higher fluorescence quantum yields.
Unusual absence of FRET in triazole bridged coumarin-hydroxyquinoline, an active sensor forHg<sup>2+</sup>detection Surajit Mondal, Niladri Patra, Hari Pada Nayek, Sumit K. Hira, Soumit Chatterjee, and Swapan Dey Springer Science and Business Media LLC A triazole-bridged coumarin conjugated quinoline sensor has been 'click'-synthesized by Cu(i) catalyzed Huisgen cycloaddition, and it exhibited high selectivity for toxic Hg2+. Surprisingly, no evidence of energy transfer from the quinoline moiety to coumarin has been found, substantiated by time-resolved fluorescence study. The possible binding mode of this sensor to Hg2+ has been established via NMR study, steady-state and time-resolved fluorescence spectroscopy, which is further supported by TDDFT calculations. The sensor has been found to be cell membrane permeable and non-toxic, and hence is suitable for intracellular Hg2+ detection.
Room-Temperature Dual Fluorescence of a Locked Green Fluorescent Protein Chromophore Analogue Soumit Chatterjee, Ketan Ahire, and Peter Karuso American Chemical Society (ACS) A structurally locked GFP chromophore with a phenyl group at C(2) of the imidazolone has been synthesized. Rotation around the exocyclic double bond is hindered, resulting in room temperature fluorescence. The quantum yield in water is 500 times greater than that of unlocked analogues. Unlike the methyl-substituted analogue, the phenyl analogue exhibits a dual emission (cyan and red) that can be used for ultrasensitive ratiometric measurements and fluorescence microscopy. To explain this dual emission, DFT calculations were car-ried out along with fluorescence upconversion experiments. The Z-isomer was found to be emissive, while the origin of the dual emission was dependent on the phenyl group in the Z-isomer, which stabilizes the Franck-Condon state, resulting a cyan fluorescence while the zwitterionic tautomer fluoresces red. These results bring important new insights into the photophysics of the GFP chromophore and provide a new scaffold capable of dual emission with utility in biotechnology.
Role of dispersive fluorous interaction in the solvation dynamics of the perfluoro group containing molecules Saptarsi Mondal, Soumit Chatterjee, Ritaban Halder, Biman Jana, and Prashant Chandra Singh American Chemical Society (ACS) Perfluoro group containing molecules possess an important self-aggregation property through the fluorous (F···F) interaction which makes them useful for diverse applications such as medicinal chemistry, separation techniques, polymer technology, and biology. In this article, we have investigated the solvation dynamics of coumarin-153 (C153) and coumarin-6H (C6H) in ethanol (ETH), 2-fluoroethanol (MFE), and 2,2,2-trifluoroethanol (TFE) using the femtosecond upconversion technique and molecular dynamics (MD) simulation to understand the role of fluorous interaction between the solute and solvent molecules in the solvation dynamics of perfluoro group containing molecules. The femtosecond upconversion data show that the time scales of solvation dynamics of C6H in ETH, MFE, and TFE are approximately the same whereas the solvation dynamics of C153 in TFE is slow as compared to that of ETH and MFE. It has also been observed that the time scale of solvation dynamics of C6H in ETH and MFE is higher than that of C153 in the same solvents. MD simulation results show a qualitative agreement with the experimental data in terms of the time scale of the slow components of the solvation for all the systems. The experimental and simulation studies combined lead to the conclusion that the solvation dynamics of C6H in all solvents as well as C153 in ETH and MFE is mostly governed by the charge distribution of ester moieties (C═O and O) of dye molecules whereas the solvation of C153 in TFE is predominantly due to the dispersive fluorous interaction (F···F) between the perfluoro groups of the C153 and solvent molecules.
Roll separating force in hot rolling under grooved rolls – A finite element analysis and experimental validation
Excited state dynamics of brightly fluorescent second generation epicocconone analogues Soumit Chatterjee, Peter Karuso, Agathe Boulangé, Xavier Franck, and Anindya Datta American Chemical Society (ACS) The natural product epicocconone, owing to its unique fluorescence properties, has been developed into a range of products used in biotechnology, especially proteomics. However, its weak green fluorescence in its native state, while advantageous for proteomics applications, is a disadvantage in other applications that require two-color readouts. Here we report the photophysical characterization of two brightly fluorescent analogues of epicocconone. These analogues, with naphthyl or pyridyl groups replacing the heptatriene chain, resulted in bright fluorescence in both the native state and the long Stokes shifted enamine. Time-resolved fluorescence studies and DFT calculations were carried out to understand the excited state processes involved in fluorescence. Results showed the p-chloro group on the pyridyl is responsible for the high fluorescence of the native fluorophore. The application of one of these compounds for staining electrophoresis gels is exemplified.
The role of different structural motifs in the ultrafast dynamics of second generation protein stains Soumit Chatterjee, Peter Karuso, Agathe Boulangé, Philippe A. Peixoto, Xavier Franck, and Anindya Datta American Chemical Society (ACS) Engineering the properties of fluorescent probes through modifications of the fluorophore structure has become a subject of interest in recent times. By doing this, the photophysical and photochemical properties of the modified fluorophore can be understood and this can guide the design and synthesis of better fluorophores for use in biotechnology. In this work, the electronic spectra and fluorescence decay kinetics of four analogues of the fluorescent natural product epicocconone were investigated. Epicocconone is unique in that the native state is weakly green fluorescent, whereas the enamine formed reversibly with proteins is highly emissive in the red. It was found that the ultrafast dynamics of the analogues depends profoundly on the H-bonding effect of solvents and solvent viscosity though solvent polarity also plays a role. Comparing the steady state and time-resolved data, the weak fluorescence of epicocconone in its native state is most likely due to the photoisomerization of the hydrocarbon side chain, while the keto enol moiety also has a role to play in determining the fluorescence quantum yield. This understanding is expected to aid the design of better protein stains from the same family.
Ultrafast dynamics of epicocconone, a second generation fluorescent protein stain Soumit Chatterjee, Tarak Nath Burai, Peter Karuso, and Anindya Datta American Chemical Society (ACS) Femtosecond upconversion experiment has been carried out for epicocconone and its butylamine adduct in acetonitrile and tert-butanol. An ultrafast component is found to dominate the decay of fluorescence of epicocconone in acetonitrile solution. Upon reacting with butylamine, a model for the epicocconone-protein adduct, this ultrafast component remains almost unaffected but an additional rise time occurs, indicating the formation of a highly emissive species from the locally excited state. This phenomenon is central to the extraordinary applications of epicocconone in biotechnology. The magnitude of the rise time of the butylamine adduct is similar to that of the longer component of the decay of epicocconone in acetonitrile, suggesting that the dynamics of epicocconone and its butylamine adduct are similar. The ultrafast component is slowed upon increasing the viscosity of the solvent. This results in a marked increase in quantum yield and suggests that it corresponds to rapid bond isomerization, leading to a nonradiative decay. Surprisingly, in water/sucrose mixtures, the ultrafast component remains unaffected but there is still an increase in quantum yield, suggesting that there are at least two nonradiative pathways, one involving bond isomerization and another involving proton transfer. The correct interpretation of these data will allow the design of second generation protein stains based on the epicocconone scaffold with increased quantum yields and photostability.
Role of spacer in single- or two-step FRET: Studies in the presence of two connected cryptands with properly chosen fluorophores Kalyan K. Sadhu, Soumit Chatterjee, Susan Sen, and Parimal K. Bharadwaj Royal Society of Chemistry (RSC) Two cryptand molecules are connected via p-xyloyl, benzene-1,4-dicarbolyol and 9,10-dimethylene anthracene. Each cryptand is further derivatized with fluorophores such that electronic absorption of one fluorophore overlaps emission of the other. This way, three different systems L(1), L(2) and L(3) have been synthesized to get a better view of the effect on the distance in single- and two-step fluorescence resonance energy transfer (FRET) process. These molecules are probed for FRET in the presence of a metal ion as input. L(1) and L(2) exhibit poor performance in single step FRET while in the case of L(3), a large two-step FRET process is operational with Cu(II) or Hg(II) as input.