Browsing by Author "Arumugaperumal, Reguram"

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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
;
Raju, Mandapati V. Ramakrishnam
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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.
Controlled Sol-Gel and Diversiform Nanostructure Transitions by Photoresponsive Molecular Switching of Tetraphenylethene- and Azobenzene-Functionalized Organogelators
(2020-07-01)
Arumugaperumal, Reguram
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Hua, Wei-Ling
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Raghunath, Putikam
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Lin, Ming-Chang
;
Chung, Wen-Sheng
The implementation of stimuli-responsive materials with dynamically controllable features has long been an important objective that challenges chemists in the materials science field. We report here the synthesis and characterization of [2]rotaxanes (R1 and R1-b) with a molecular shuttle and photoresponsive properties. Axles T1 and T1-b were found to be highly efficient and versatile organogelators toward various nonpolar organic solvents, especially p-xylene, with critical gelation concentrations as low as 0.67 and 0.38 w/v %, respectively. The two molecular stations of switchable [2]rotaxanes (R1 and R1-b) can be revealed or concealed by t-butylcalix[4]arene macrocycle, thus inhibiting the gelation processes of the respective axles T1 and T1-b through the control of intermolecular hydrogen-bonding interactions. The sol-gel transition of axles T1 and T1-b could be achieved by the irradiation of UV-visible light, which interconverted between the extended and contracted forms. Interestingly, the morphologies of organogels in p-xylene, including flakes, nanobelts, fibers, and vesicles depending on the molecular structures of axles T1 and T1-b, were induced by UV-visible light irradiation. Further studies revealed that acid-base-controllable and reversible self-assembled nanostructures of these axle molecules were mainly constructed by the interplay of multi-noncovalent interactions, such as intermolecular pi-pi stacking, CH-pi, and intermolecular hydrogen-bonding interactions. Surprisingly, our TPE molecular systems (R1, R1-b, T1, and T1-b) are nonemissive in their aggregated states, suggesting that not only fluorescence resonance energy transfer but also aggregation-caused quenching may have been functioning. Finally, the mechanical strength of these organogels in various solvents was monitored by rheological experiments.
Distinct Nanostructures and Organogel Driven by Reversible Molecular Switching of a Tetraphenylethene-Involved Calix[4]arene-Based Amphiphilic [2]Rotaxane
(2018-10-23)
Arumugaperumal, Reguram
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Raghunath, Putikam
;
Lin, Ming-Chang
;
Chung, Wen-Sheng
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應用化學系
Aggregation induced emission (AIE) active and acid/base controllable amphiphilic [2]rotaxanes R1 and R2 were successfully constructed with tetraphenylethene (TPE) as a stopper and t-butylcalix[4]arene or calix[4]arene macrocycle as a wheel over the axle component. The AIE effect of [2]rotaxanes R1 and R2 was greatly affected by the molecular shuttling of t-butylcalix[4]arene or calix[4]arene macrocycle, which was triggered by the acid/base strategy. In the case of [2]rotaxane R1, aggregation was achieved in the presence of less amount of water compared with those of [2]rotaxane R2, and the deprotonated [2]rotaxanes R1-b and R2-b, owing to the stronger interaction between the TPE and t-butylcalix[4]arene macrocycle and restricted intramolecular rotation (RIR), thus making it responses in less quantity of water along with highly fluorescent emission. [2]Rotaxane R1-b started to aggregate at 70% water fraction (f(w)), while [2]rotaxane R2-b started to aggregate at 75% f(w) which allowed them to morph into hollow nanospheres, whereas they formed only nanospheres at 99% f(w) in CH3CN/water cosolvent system due to the higher degree of aggregation in aqueous media. To our delight, controllable morphology of self-assembled structures was indeed formed from these [2]rotaxanes. Interestingly, by the interplay of a wide range of multi-self-assembly driving forces, the slack stacking of rotaxane unit forms a hollow on the surface of nanospheres to become hollow nanospheres. Among the four [2]rotaxanes studied here, R1 possessed a narrower HOMO-LUMO band gap compared to those others, as confirmed by computational study. Furthermore, only [2]rotaxane R1 formed organogel in methanol solvent and its reversible gel-sol transition could be achieved by the addition of acid and base. This implies that the formation of dumbbell shape cross-linked 3D network structures were mainly governed by pi-pi stacking, van der Waals force, and intermolecular H-bonding interactions during the gelation processes.
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
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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.
Facile rhodamine-based colorimetric sensors for sequential detections of Cu(II) ions and pyrophosphate (P2O74-) anions
(2016-01-01)
Arumugaperumal, Reguram
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Srinivasadesikan, Venkatesan
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Lin, Ming-Chang
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Shellaiah, Muthaiah
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Shukla, Tarun
Two rhodamine hydrazine derivatives Rh1 and Rh2 with catechol and ether functionalities have been synthesized and utilized towards sequential colorimetric detections of Cu(II) and pyrophosphate (PPi) ions in CH3CN-H2O (v/v = 9 : 1, 5 mM Tris-HCl, pH 7.4) semi-aqueous medium. Notably, Rh1 and Rh2 are the first example of colorimetric rhodamine-based probes for the sequential detections of Cu2+ ion and PPi anion. Based on the significant colorimetric responses (from colorless to pink) of Rh1 and Rh2 to Cu2+ ions, the detection limits were estimated as low as 1.22 x 10(-8) M and 8.0 x 10(-7) M, respectively, which signified the utilities of designed probes towards facile detections of Cu2+ ions. Furthermore, upon the successive addition of PPi ion to Rh1-Cu2+ and Rh2-Cu2+ complexes, it has been altered and restored to its origin of Rh1 and Rh2 via re-coordination of PPi to Cu2+ ion, which was confirmed by color changes from pink to colorless. Moreover, computational DFT calculations provided more insights into HOMO-LUMO structures of rhodamine derivatives and their copper complexes. Additionally, the solid state strip-based colorimetric detections of Cu2+ ion were supplemented as a real time application.
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
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Raghunath, Putikam
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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 supramolecular conjugated polyrotaxane as an acid-base controllable optical molecular switch
(2017-05-01)
Shukla, Tarun
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Arumugaperumal, Reguram
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Raghunath, Putikam
;
Lin, Ming-Chang
;
Lin, Chien-Min
To study the supramolecular interactions of the mechanically interlocked rotaxane pendants with the backbone of two comparable conjugated polymers, axle polymer P1 and polyrotaxane P2 were synthesized by copolymerization of fluorine-based monomer F with phenanthroimidazole (PIZ)-based axle monomer A and rotaxane monomer R, respectively. Prevailing H-1 NMR, UV-vis and PL profiles revealed that polyrotaxane P2 showed sensitive and reversible acid-base molecular switching properties via supramolecular interactions in contrast to the other analogous polymer P1. The capability of molecular switching is also proven by computational study. Apparently, the controllable nano self-assembly process of P2 was fulfilled by reversible acid-base molecular switch approaches, where the orthogonal H-bonded polyrotaxane units were converted from bloated form into flake form on protonation. (C) 2016 Elsevier B.V. All rights reserved.
Synthesis and study of hybrid hydrogen-bonded bent-core liquid crystal complexes containing C-60- and Si-based proton donors
(2015-01-01)
Liu, Shih-Hsien
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Yang, Po-Jen
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Wei, Chong-Lun
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Chiang, I. -Hung
;
Liao, Chun-Yen
Novel hydrogen-bonded (H-bonded) C-60- and Si-based bent-core liquid crystal (LC) complexes containing a bent-shaped proton acceptor and C-60- and Si-based single/double armed proton donors were synthesized and mixed to produce hybrid H-bonded LC complexes. The SmCP phases could be introduced in the hybrid LC complexes with a very high C-60-based moiety up to 90 mol%. Among our H-bonded LC complexes, the hybrid LC complexes with low amounts of the C-60-based moiety (<= 24 mol%) possessed the highest spontaneous polarization value (ca. 494 nC cm(-2)), the widest mesophasic range (40.8 degrees C) and the lowest saturated electric field (8.8 V-pp mu m(-1)). Under electric fields of modified triangle waveforms, both series of hybrid H-bonded LC complexes displayed an anti-ferroelectric (AF) to a ferroelectric (FE) polar switching as the C-60-based moiety increased up to 24-50 mol%. Therefore, the hybrid H-bonded LC complexes containing a broad molar ratio (0-90 mol%) of C-60-based moiety revealed a tunable route for the electro-optical applications of C-60-based H-bonded liquid crystals.