Browsing by Author "Singh, Ravinder"

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A new pyrene-based aggregation induced ratiometric emission probe for selective detections of trivalent metal ions and its living cell application
(2015-02-01)
Singh, Ashutosh
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Singh, Ravinder
;
Shellaiah, Muthaiah
;
Prakash, Epperla Chandra
;
Chang, Huan-Cheng
We synthesize a newly designed pyrene-based fluorescent probe FBP containing a Schiff base and amide linkage as a receptor, which demonstrates selective UV-vis and fluorometric detections of trivalent metal ions in various semi-aqueous solution conditions. Interestingly, by increasing water contents the aggregation induced ratiometric emissions (AIREs) of photoluminescence in FBP solutions (in DMSO/H2O) are enhanced from blue to green due to the excimer formation of the aggregates in water. In addition, the enhanced aggregated ratiometric green fluorescence behaviors of FBP in the presence of trivalent metal ions (Al3+, Fe3+, and Cr3+) are observed in semi-aqueous solutions as well as the solid state, which is well utilized to detect trivalent metal ions in living cells. Further verification of the probe detections, their interactions toward trivalent metal ions are well characterized by the time-resolved photoluminescence (TRPL) of spectroscopic responses as well as theoretical calculations. Therefore, we believe the application of such a new AIRE-based approach is first reported among Schiff base and pyrene-based fluorescentchemo- and bio-sensors. (C) 2014 Elsevier B.V. All rights reserved.
Acid/Base and H2PO4- Controllable High-Contrast Optical Molecular Switches with a Novel BODIPY Functionalized [2]Rotaxane
(2015-12-09)
Arumugaperumal, Reguram
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Srinivasadesikan, Venkatesan
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Raju, Mandapati V. Ramakrishnam
;
Lin, Ming-Chang
;
Shukla, Tarun
A novel multifunctional mechanically interlocked switchable [2]rotaxane R4 containing two molecular stations and rotaxane arms terminated with boron-dipyrromethene (BODIPY) fluorophores and its derivatives were synthesized for the first time by CuAAC click reaction. The shuttling motion of macrocyde between the dibenzylammonium and triazolium recognition sites and the distance dependent photoinduced electron transfer process of R4 is demonstrated by utilizing external chemical stimuli (acid/base). Interestingly, the reversible self-assembly process of R4 was recognized by the acid-base molecular switch strategy. Notably, two symmetrical triazolium groups acted as molecular stations, H2PO4- receptors, and H-bonded donors. Both [2]rotaxane R4 and thread R2 demonstrated excellent optical responses and high selectivity toward H2PO4- ion. The specific motion and guest-host interactions of mechanically interlocked machines (MIMs) were also further explored by quantum mechanical calculations. The thread R2 also demonstrated to enable the detection of H2PO4- in RAW 264.7 cells successfully.
Exploration of Energy Modulations in Novel RhB-TPE-Based Bichromophoric Materials via Interactions of Cu2+ Ion under Various Semiaqueous and Micellar Conditions
(2016-03-16)
Singh, Ravinder
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Dwivedi, Atul Kumar
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Singh, Ashutosh
;
Lin, Chien-Min
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Arumugaperumal, Reguram
Novel bichromophoric materials TR-A and TR-B consisting of an entirely new combination of TPE and RhB units were developed to explore the optimum conditions of energy modulations via pH variation and Cu2+ interaction at various water contents of CH3CN. Interestingly, TR-A and TR-B, at 60 and 70% water contents; respectively, favored the optimum Cu2+-mediated energy modulations from TPE to RhB and thus achieve the brightest orange emissions of free RhB with complete disappearance of aggregation-induced emission (AIE) from TPE. Furthermore, various micellar conditions of triton-X-100, SDS, and CTAB were employed to adjust energy modulations of TR-A and TR-B at high water contents (at 80 and 90%, respectively). The incorporation of RhB into triton-X-100 micellar cavities disrupted AIE from TPE; thus, none of the energy modulations from TPE to RhB occurred even in the presence of Cu2+ ion. Interestingly, the micellar conditions of anionic surfactant (SDS) favored the increased local concentration of Cu2+ ions in the vicinity of scavangable RhB and facilitated the generation of noncyclic free RhB in situ via bright-orange emissions.
Monomeric and aggregation emissions of tetraphenylethene in a photo-switchable polymer controlled by cyclization of diarylethene and solvent conditions
(2017-10-14)
Singh, Ravinder
;
Wu, Hsin-Yen
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Dwivedi, Atul Kumar
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Singh, Ashutosh
;
Lin, Chien-Min
A novel photo-switchable polymer P-PHT containing diarylethene (DAE) and tetraphenylethene (TPE) moieties and a triazole linker in the repeating unit was synthesized to study the aggregation-induced emission (AIE) behaviour of TPE with both the open and closed forms of DAE in P-PHT with high water contents. The photo-switching phenomena of DAE (from open to closed forms under UV-irradiation) in P-PHT were prominent in organic solvent (THF), high water contents (at 90% H2O) and acidic conditions. Upon UV-irradiation of P-PHT at 90% water content, the AIE of TPE was completely quenched via an energy transfer event from TPE to cyclized DAE. Interestingly, the rare monomeric emission of TPE was first discovered by the photo-cyclization of DAE in P-PHT compared with the AIE behaviour of TPE with the open form of DAE in P-PHT with AIE favourable conditions of high water content (90% H2O) and acidic conditions.
Multi-stimuli-responsive high contrast fluorescence molecular controls with a far-red emitting BODIPY-based [2]rotaxane
(2018-10-01)
Arumugaperumal, Reguram
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Venkatesan, Parthiban
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Shukla, Tarun
;
Raghunath, Putikam
;
Singh, Ravinder
A novel fluorescent switchable [2]rotaxane NIR4 composed of two different molecular stations and rotaxane arms terminated with far-red boron-dipyrromethene (BODIPY) fluorophores and its derivatives were synthesized by CuAAC click chemistry. The molecular shuttling motion of mechanically interlocked molecules (MIMs) could be addressed by the fluorescence signal transduction via distance dependent photo-induced electron transfer process of [2]rotaxane NIR4 triggered by external chemical stimuli of acid/base. Moreover, the flexible arms of triazolium moiety in [2]rotaxane NIR4 and its axle NIR2 exhibited impressive selectivity and sensitivity toward complementary anionic analyte (H2PO4-), where the specific mechanical molecular motion was supported by quantum mechanical calculations. The development of [2]rotaxane NIR4 with a high level of structural complexity can be utilized for novel dual sensory detections of acid-base and dihydrogen phosphate (H2PO4-) anion. Importantly, the host of NIR2 and [2]rotaxane NIR4 could be applied for the vitro imaging and clarify the distribution of H2PO4- at subcellular levels.
Novel fluoride-substituted donor/acceptor polymers containing benzodithiophene and quinoxaline units for use in low-band gap solar cells
(2016-09)
Singh, Ashutosh
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Singh, Ravinder
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Lin, Chein-Min
;
Pola, Murali Krishna
;
Chang, Chiao-Kai
In this study we used Stille polycondensation to synthesize a series of low-band gap fluoride-substituted conjugated polymers containing electron-donating benzodithiophene (BDT) and electron-accepting quinoxaline (Qx) units, with the latter presenting either two or four fluoride atoms. These donor/acceptor polymers exhibited a broad absorption range (from 300 to 750 nm), with band gap energies of less than 1.20 eV (measured using cyclic voltammetry). Because of their strongly electron-donating thiophene units, the donor/acceptor polymers featuring the more highly fluorinated structures possessed the lowest band gaps (as low as 1.14 eV) and, thus, induced the greatest photovoltaic performance among these tested polymers. The highest power conversion efficiency (2.13%) was obtained from the polymer solar cell featuring an active layer of the polymer PTF2 blended with PC70BM (1:1.5, w/w), with a short-circuit current density, open circuit voltage, and fill factor of 8.7 mA cm(-2), 0.72 V, and 0.34, respectively. (C) 2016 Elsevier Ltd. All rights reserved.
Novel Water-Soluble Cyclodextrin-Based Conjugated Polymer for Selective Host-Guest Interactions of Cationic Surfactant CTAB and Reverse FRET with Rhodamine B Tagged Adamantyl Guest
(2016-08-09)
Dwivedi, Atul Kumar
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Singh, Ravinder
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Singh, Ashutosh
;
Wei, Kung-Hwa
;
Wu, Chu-Ya
A new water-soluble pi-conjugated main-chain polymer P1 bearing a beta-cyclodextrin (beta-CD) pendant was designed and synthesized. The aggregation and disaggregation of P1 generated faded yellow-greenish and bright-yellow emissions, respectively. The inclusion complexation capability of P1 through beta-CD pendant with a cationic surfactant cetyltrimethylammonium bromide (CTAB) guest and associative interactions of P1 with Fe3+ through triazole spacers resulted in significantly enhanced and completely diminished emission profiles of P1 in pure water, respectively. Interestingly, ADRhB as another rhodamine B (RhB) tagged adamantyl guest was transformed into ADRhB(0), i.e., the open form of ADRhB, to generate RhB emission in the presence of Fe3+ ion selectively for the pendent host beta-CD of PI, and the further interaction of.ADRhB(0)/Fe3+ with P1 prevailed a completely quenched RhB emission via the inclusion complexation of adamantyl terminal of ADRhB (0) in beta-CD. Moreover, stronger interactions of CTAB with beta-CD further generated RhB emission of ADRhB(0) even in the presence of acceptor Pl. Finally, a novel beta-CD bearing water-soluble P1 with selective and strong interactions of CTAB toward disaggregation events in pure water, and further electrostatic repulsion and utilization of RhB via RhB-tagged adamantyl guest ADRhB(0) as a donor revealed the reverse fluorescence resonance energy transfer (FRET) process of P1.