Sougata Sinha

Imine containing benzophenone scaffold as an efficient chemical device to detect selectively Al3

A benzophenone-based Schiff base 1 has been utilized as a fluorescence chemosensor for the selective detection of Al3+. The probe was synthesized in one step, and found to be non-fluorescent due to a combination of photoinduced electron transfer (PET), excited state intramolecular proton transfer (ESIPT) and E/Z isomerism. Upon addition of Al3+ to a methanolic solution of 1, the development of a strong fluorescence signal was observed with an attractive glowing green emission. This was due to the inhibition of PET, ESIPT and E/Z isomerism, and the activation of chelation enhanced fluorescence (CHEF). The quantum yield of 1–Al3+ was found to be 0.17. The selectivity was tested with 24 different metal and non-metal ions, and established using various spectroscopic tools. The strong affinity of compound 1 for Al3+ was also proven by 1H NMR and mass spectroscopy.

Triazole-based Zn2+-specific molecular marker for fluorescence bioimaging

Fluorescence bioimaging potential, both in vitro and in vivo, of a yellow emissive triazole-based molecular marker has been investigated and demonstrated. Three different kinds of cells, viz Bacillus thuringiensis, Candida albicans, and Techoma stans pollen grains were used to investigate the intracellular zinc imaging potential of 1 (in vitro studies). Fluorescence imaging of translocation of zinc through the stem of small herb, Peperomia pellucida, having transparent stem proved in vivo bioimaging capability of 1. This approach will enable in screening cell permeability and biostability of a newly developed probe. Similarly, the current method for detection and localization of zinc in Gram seed sprouts could be an easy and potential alternative of the existing analytical methods to investigate the efficiency of various strategies applied for increasing zinc-content in cereal crops. The probe-zinc ensemble has efficiently been applied for detecting phosphate-based biomolecules.

Engineering fused coumarin dyes: a molecular level understanding of aggregation quenching and tuning electroluminescence via alkyl chain substitution

Simple molecular structures capable of emitting over the entire visible range are still a challenge. Planar molecular structures have the drawback of fluorescence quenching in the solid state thus limiting their application fields. Combining long range excimer/exciplex emissions with a compound emission have been used to get white light. In this work, a series of new coumarin derivatives having a planar structure have been synthesized and characterized. The effects of systematic variation in alkyl chain functionalization providing morphological variations that permit interesting solid state emitting properties have been discussed simultaneously with electrochemical behavior and OLED (organic light emitting diode) device applications. Carbon chains containing 0–16 carbon atoms have been studied in order to conclude the results that systematic changes in alkyl group substitution can be utilized as a tool to tune the emitting color of these planar coumarins. Alkyl chains were introduced by O-acylation and O-benzoylation reaction on the hydroxyl group of parent coumarin 5. Thus the present strategy is also helpful in establishing a template to control the unproductive interchromophore electronic couplings. Solid state fluorescence properties support the crystal studies. Theoretical studies are also in agreement with experimental data. Electroluminescence of Device 2 with a turn on voltage (Von) around 5–6 V having s-CBP doped with 1% of 8 having alkyl substitution of 2-carbons is found to exhibit white emission with CIE co-ordinates of (0.29, 0.34) which is close to white emission while the alkyl substitution of 14-carbons (compound 17) in Device 7 (Von = 7 V) exhibited green emission. Thus a strategy helpful to tune the electroluminescence has been discussed.

Cysteamine-based cell-permeable Zn(2+)-specific molecular bioimaging materials: from animal to plant cells.

Structure-interaction/fluorescence relationship studies led to the development of a small chemical library of Zn(2+)-specific cysteamine-based molecular probes. The probe L5 with higher excitation/emission wavelengths, which absorbs in the visible region and emits in the green, was chosen as a model imaging material for biological studies. After successful imaging of intracellular zinc in four different kinds of cells including living organisms, plant, and animal cells, in vivo imaging potential of L5 was evaluated using plant systems. In vivo imaging of translocation of zinc through the stem of a small herb with a transparent stem, Peperomia pellucida, confirmed the stability of L5 inside biological systems and the suitability of L5 for real-time analysis. Similarly, fluorescence imaging of zinc in gram sprouts revealed the efficacy of the probe in the detection and localization of zinc in cereal crops. This imaging technique will help in knowing the efficiency of various techniques used for zinc enrichment of cereal crops. Computational analyses were carried out to better understand the structure, the formation of probe-Zn(2+) complexes, and the emission properties of these complexes.

Exploring 1,4-dihydroxyanthraquinone as long-range emissive ratiometric fluorescent probe for signaling Zn2+/PO43−: Ensemble utilization for live cell imaging

Fluorescent 1,4-dihydroxyanthraquinone 1 was found to demonstrate its ratiometric signaling property upon interaction with divalent zinc (Zn(2+)). While the probe itself exhibited fluorescence emission in the yellow region (λem=544 nm and 567 nm), binding with Zn(2+) induced strong emission in the orange region (λem=600 nm) which was mainly due to a combination of CHEF and ICT mechanism. The probe was found to be highly sensitive toward the detection of zinc and the limit of detection (LOD) was calculated to be 9×10(-7) M. The possibility of using this probe for real-time analysis was strongly supported by the striking stability of fluorescence signal for more than five days with similar fluorescence intensity as observed during instant signaling. The present probe works within physiological pH range and is devoid of any interference caused by the same group elements such as Cd(2+)/Hg(2+). The probe possesses excellent excitation/emission wavelength profile and can penetrate cell membrane to image low concentration of zing inside living system. The in situ formed zinc-probe ensemble was further explored as ratiometric sensing platform for detecting another bio-relevant analyte phosphate anion through a zinc-displacement approach.

Carboxylated ‘locking unit’ directed ratiometric probe design, synthesis and application in selective recognition of Fe3+/Cu2+

A ratiometric probe has been designed and synthesized through the introduction of a carboxylated functionality. The probe 1, synthesized in two steps, was found to be a fluorescent chemosensor for the selective ratiometric detection of Fe3+/Cu2+ over a wide range of metal ions quite efficiently. The carboxylated unit, ‘CH2COOH’, acts as a ‘locking unit’ restricting the possibility of E/Z isomerization and ESPT. This has been supported by theoretical studies. The selectivity was established using various spectroscopic techniques such as UV-vis and fluorescence spectroscopy. The probe was found to have fluorescence properties with a quantum yield of 0.18. The binding of this fluorescent receptor to metal ions was also proved by NMR and mass spectrometry. The present probe can efficiently detect the presence of very low concentrations of Fe3+/Cu2+ (0.51 and 4.46 μM of Cu2+ and Fe3+ respectively).

Tri-color emission and colorimetric recognition of acetate using semicarbazide and thio-semicarbazide derivatives: Experimental and computational studies

Two new fluorescence probes having semicarbazide (DSC) and thio-semicarbazide (DTSC) units have been derived upon reaction with 2-hydroxy-5-methylbenzene-1,3-dialdehyde. Both the probes show excellent selectivity for acetate ion in DMSO medium whereby DTSC generates tricolor emission. The association constants of DSC and DTSC for acetate are 6.6×10(4)M(-1) and 2×10(3)M(-1) respectively with corresponding detection limits, 1.06×10(-7)M and 2.5×10(-6)M. Density functional theoretical (DFT) studies nicely demonstrate the interaction between the DTSC and acetate ion.