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Parthasarathy Gayathri

Bio: Parthasarathy Gayathri is an academic researcher from Department of Biotechnology. The author has contributed to research in topics: Fluorescence & Chemistry. The author has an hindex of 5, co-authored 11 publications receiving 66 citations. Previous affiliations of Parthasarathy Gayathri include Shanmugha Arts, Science, Technology & Research Academy.

Papers
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Journal ArticleDOI
TL;DR: In this article, the authors presented the recent developments in ESIPT-based solid state fluorescent materials and external stimuli-induced fluorescence switching and showed that the substitutional unit, molecular conformation and supramolecular interactions played a significant role in transforming planar ESIPt fluorophores to stimuli-induced fluorescent switching materials either between two states or off-on states.
Abstract: Stimuli-responsive organic solid state fluorescent materials are considered as potential candidates for optoelectronic application as well as in the biomedical field. Molecular design and supramolecular interaction controlled organization in the solid state played an important role in producing switchable and tunable fluorescent materials. Excited state intramolecular proton transfer (ESIPT) mechanism-based solid state fluorescent materials showed unique photophysical properties such as a large Stokes shift and local environment (pH, polarity, ions and viscosity) responsive fluorescence modulation. The unique photophysical properties of ESIPT molecules made them interesting for various fields including laser dyes, molecular probes, optoelectronics, white emissive materials and optical information storage materials. Systematic fluorophore structural engineering has been performed over the years to gain insight on the ESIPT mechanism in order to improve the quantum efficiency and introduce desirable material attributes for functional applications. The substitutional unit, molecular conformation and supramolecular interactions played a significant role in transforming planar ESIPT fluorophores to stimuli-induced fluorescence switching materials either between two states or off–on states. In this review article, we have presented the recent developments in ESIPT-based solid state fluorescent materials and external stimuli-induced fluorescence switching.

34 citations

Journal ArticleDOI
TL;DR: Triphenylamine (TPA) and N-methylbarbituric acid/indanedione-based donor-acceptor derivatives were synthesized and demonstrated molecular conformation and packing dependent tunable fluorescence from yellow to red in the solid state.
Abstract: Triphenylamine (TPA) and N-methylbarbituric acid/indanedione-based donor–acceptor derivatives were synthesized and demonstrated molecular conformation and packing dependent tunable fluorescence from yellow to red in the solid state. TPA with N-methylbarbituric acid (BA-1) showed bright yellow fluorescence (λmax = 550 nm, Φf = 22.8%) whereas OCH3 substitution at the phenyl rings of TPA, (BA-2 and BA-3) produced strong red (λmax = 602 nm, Φf = 41.1%) and orange fluorescent solids (λmax = 582 nm, Φf = 19.1%). Indanedione acceptor dyes exhibited red to deep red fluorescence. ID-1 showed red fluorescence at 604 nm (Φf = 17.7%) whereas ID-2 and ID-3 showed fluorescence at 611 (Φf = 19.4%) and 636 nm (Φf = 14.1%) in the solid state. Solid state structural analysis revealed alteration of the molecular conformation and packing by OCH3 substitution which led to tunable fluorescence. BA and ID compounds showed turn-off fluorescence/substantially reduced fluorescence intensity upon hard crushing (Φf = 1.2 to 3.1%). Interestingly, heating of BA and ID crushed powders led to turn-on fluorescence/significant enhancement of fluorescence intensity (Φf = 5.6 to 22.5%). Powder X-ray diffraction (PXRD) studies indicated the conversion of the crystalline phase to amorphous and the amorphous phase to crystalline by hard crushing and heating. The reversible conversion of the crystalline phase to amorphous phase was responsible for the fluorescence switching of BA and ID. Computational studies have been performed to get an insight into the energy level modulation upon the change of the molecular conformation. Thus, we have presented the facile preparation of strong red fluorescent dyes exhibiting high contrast stimuli-responsive reversible dark and bright fluorescence switching in the solid state.

27 citations

Journal ArticleDOI
TL;DR: In this article, a donor-acceptor derivatives of halogen-substituted positional isomers were synthesized and the effect of the halogen and position on the solid-state fluorescence and mechanofluorochromism was explored.
Abstract: Carbazole-based donor–acceptor derivatives of halogen-substituted positional isomers were synthesised and the effect of the halogen and position on the solid-state fluorescence and mechanofluorochromism was explored. All compounds showed good solid-state fluorescence (Φf = 15.67 to 31.32%). Interestingly, the crystallization of the positional isomers produced concomitant blue and green fluorescent polymorphs and tunable solid-state fluorescence. Solid-state structural analysis revealed a subtle conformational change in the acceptor unit, which led to polymorphism and tunable fluorescence. Halogen substitution induced a higher conformational twist and a large fluorescence shift between the polymorphs. The supramolecular interactions (H-bonding, C–H⋯π and π⋯π) observed in the crystal lattice rigidified the fluorophores and enhanced the solid-state fluorescence. Computational studies were performed to gain insights into the electronic energy level of the fluorophore and fluorescence modulation. All fluorophores showed mechanofluorochromism (MFC), reversible fluorescence switching, upon crushing and heating. The crushed solids also showed self-reversible fluorescence switching with a longer time. Interestingly, OFF–ON reversible fluorescence switching was also demonstrated by melting and warming/scratching. The powder X-ray diffraction studies supported self-reversible and crystallization-induced fluorescence switching.

22 citations

Journal ArticleDOI
11 Sep 2017
TL;DR: In this paper, the influence of alkyl chain length on the molecular conformations and packing of aggregation enhanced emissive (AEE) triphenylamine fluorophore and tune the fluorescence maxima and mechano/thermochromism.
Abstract: Flexible alkyl chain has been used to control the molecular conformation, packing and intermolecular interactions of aggregation enhanced emissive (AEE) triphenylamine fluorophore, and tune the fluorescence maxima and mechano/thermochromism. 2-(4-(diphenylamino)-2-ethoxybenzylidene)malononitrile (DPABM-2), 2-(4-(diphenylamino)-2-propoxybenzylidene)malononitrile (DPABM-3), 2-(4-(diphenylamino)-2-butoxybenzylidene)malononitrile (DPA-BM-4), 2-(4-(diphenylamino)-2-pentyloxybenzylidene) malono-nitrile (DPABM-5), 2-(4-(diphenylamino)-2-hexyloxybenzylidene) malonon-itrile (DPABM-6) and 2-(4-(diphenylamino)-2-heptyloxybenzylidene) malononitrile (DPABM-7) exhibited weak to strong solid state fluorescence (absolute quantum yield (Φf)=4 to 26%). DPABM-2 did not show significant fluorescence changes to external stimuli, however, DPABM-3 and DPABM-4 exhibited off-on fluorescence switching. DPABM-3 also showed tunable fluorescence via polymorphism. Interestingly, DPABM-5-7 showed alkyl chain orientation dependent self-reversible thermochromism. DPABM-5 and DPABM-7 exhibited decrease of fluorescence intensity with temperature whereas DPABM-6 showed increase of fluorescence intensity. Solid state structural analysis revealed the influence of alkyl chain length on the molecular conformations and packing. Powder X-ray diffraction (PXRD) studies indicate that phase change of materials from crystalline to amorphous and vice-versa was responsible for fluorescence switching with external stimuli. Further, AEE of DPABM derivatives and the reactive ethylene-malononitrile has also been exploited for fabricating hydrazine sensing polymer composite film. Thus simple change of alkyl chain lengths lead to the generation of polymorphism, mechanochromism and temperature dependent self-reversible fluorescence switching materials.

19 citations

Journal ArticleDOI
15 Feb 2021
TL;DR: Pyridine appended structural isomers showed a planar or propeller conformation dependent molecular self-assembly, fluorescent polymorphs, stimuli-responsive fluorescence switching and halochromism.
Abstract: The fluorescence properties of organic materials are intrinsically governed by the molecular conformation and intermolecular interaction mediated aggregation. Herein, we have synthesized two sets of isomeric fluorescence molecules with a partially planar and propeller structure, (Z)-3-(4-(9H-carbazol-9-yl)phenyl)-2-(pyridinyl)acrylonitrile (1–3) and (Z)-3-(4-(diphenylamino)phenyl)-2-(pyridinyl)acrylonitrile (4–6) and explored their effect on the molecular aggregation, and tunable and switchable solid state fluorescence. Molecular aggregation studies revealed the formation of 1D nanostructures of nanoparticles with the evolution of intermolecular interactions with increasing water fraction and time. The evolution of nanostructures led to a tunable fluorescence from green to red. The subtle structural change and formation of different crystal forms/polymorphs resulted in a tunable fluorescence between 514 and 644 nm (Φf = 11.3 to 25.3%). Solid state structural studies showed relatively weak intermolecular interactions in the crystal lattice of 1, 3 and 6 that resulted in the formation of different crystal forms/polymorphs and varied molecular assemblies with tunable fluorescence. Mechanofluorochromism (MFC) studies also showed molecular structure dependent fluorescence switching. 1–3 and 6 showed crushing/heating induced reversible fluorescence switching whereas 4 and 5 did not show any MFC. Integrating an acid/base sensitive pyridine functionality has been exploited for demonstrating halochromic reversible fluorescence switching as well as fabricating rewritable/self-erasable fluorescent platforms on filter paper and glass plates.

18 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a series of novel smart luminescent compounds based on a cyanostyrene unit, NAIF, NA-15C5, NAPM, NAIP and NAPF, have been developed.
Abstract: Multicolor mechanochromic luminescent (MCL) materials are promising candidates in fundamental science and practical applications. In this paper, a series of novel smart luminescent compounds based on a cyanostyrene unit, NAIF, NA-15C5, NAPM, NAIP and NAPF, have been developed. NAIF, NAPM, NAPF and NAIP all exhibit aggregation-induced emission (AIE) characteristics and individually show red, orange, yellow and green emission in their aggregated state. Luminogens NA-15C5 and NAPM display reversible tricolor-changing MCL behaviors. NAIF and NAIP show bicolor switching mechanochromic phenomena. Additionally, different molecular packing modes of two crystalline polymorphs, NAPM-y and NAPM-o with bright yellow and orange luminescence color, rationally explain the tricolor-changing mechanochromic mechanism. Moreover, luminogen NAIP can be used as ink-free rewritable paper.

81 citations

Journal ArticleDOI
TL;DR: A comprehensive review of the recent development and applications of excited-state intramolecular proton transfer-based (ESIPT-based) aggregation-induced emission luminogens (AIEgens) can be found in this paper .
Abstract: In this review, we present a systematic and comprehensive summary of the recent development and applications of excited‐state intramolecular proton transfer‐based (ESIPT‐based) aggregation‐induced emission luminogens (AIEgens), a type of promising materials that inherit the advantages of ESIPT and AIE, such as large Stokes shift, excellent photostability, and low self‐quenching. We first summarize the backbones that have been used to construct the ESIPT‐based AIEgens and classify the constructed ones based on the relation between ESIPT and AIE unit. According to the sensing mechanisms and design strategies, we have reviewed the applications of ESIPT‐based AIEgens in bioimaging, drug delivery systems, organic light‐emitting diodes, photo‐patterning, liquid crystal, and the detection of metal cations, anions, small molecules, biothiols, biological enzymes, latent fingerprinting, and so on. We have also reviewed the recent advances in the development of new theoretical methods for investigating molecular photochemistry in crystals and their applications in ESIPT‐based AIEgens. We discussed the remaining challenges in this field and the issues that need to be addressed. We anticipate that this review can provide a comprehensive picture of the current condition of research in this field, and promote researchers to make more efforts to develop novel ESIPT‐based AIEgens with new applications.

55 citations

Journal ArticleDOI
TL;DR: This review focuses exclusively on TPA-based smart fluorescent materials that exhibit distinct and reversible fluorescence switching towards different stimuli and a detailed discussion of the structure–property relationships of TPA derivatives could provide insights for developing new Tpa-basedsmart fluorescent materials with versatile properties.
Abstract: Smart fluorescent materials exhibit a controlled fluorescence response to different external stimuli such as pressure, heat, light, pH, etc. Molecular structure and supramolecular assembly via weak intermolecular interactions strongly influence the fluorescence efficiency and colour. In particular, non-planar molecular structures play a significant role in developing solid state fluorescent materials. Triphenylamine (TPA), a typical non-planar propeller molecule with interesting optoelectronic properties, provides an excellent opportunity for developing a variety of molecular fluorescent materials by taking advantage of synthetic feasibility. For example, a donor–acceptor (D–A) aggregation induced emissive (AIE) fluorophore can be developed by integrating an acceptor group into the phenyl unit of a TPA donor. In this review, we focus exclusively on TPA-based smart fluorescent materials that exhibit distinct and reversible fluorescence switching towards different stimuli. Molecular engineering of the TPA fluorophore resulted in the development of different types of stimuli-responsive materials and the conformational flexibility of non-planar phenyl groups often produced polymorphism induced fluorescence tuning. A detailed discussion of the structure–property relationships of TPA derivatives could provide insights for developing new TPA-based smart fluorescent materials with versatile properties.

51 citations

Journal ArticleDOI
TL;DR: In this paper, a donor-acceptor-structured triphenylamine-functionalized unsymmetrical azine molecules (L1-L4) were constructed from 4-(hydrazonomethyl)-N,N-diphenylaniline with different salicylaldehyde derivatives.
Abstract: The development of multi-color aggregation-induced emission (AIE)-featured azine molecules with excited-state intramolecular proton transfer (ESIPT) characteristics has drawn significant interest in recent years. In this study, we report the construction of donor-acceptor-structured triphenylamine-functionalized unsymmetrical azine molecules (L1–L4) prepared from 4-(hydrazonomethyl)-N,N-diphenylaniline with different salicylaldehyde derivatives. By changing the electron donating ability at the ESIPT moiety, we could tune the optical properties of the newly synthesized molecules. All the compounds exhibited the AIE behavior in a THF/water mixture and the excited-state intramolecular proton transfer phenomenon. Further, the tuning of a peripheral substituent in the salicylaldehyde moiety resulted in different emission colors in the aggregated state. The crystal structure of all the compounds (L1–L4) revealed that the multiple weak interactions present in the solid-state structure lead to various supramolecular networks. In addition, these molecules showed a prominent positive solvatochromic effect, which was confirmed by their solvent polarity-dependent emission behavior. The appearance of dual emission bands in the solid as well as in the solution state, lifetime values and HOMO, LUMO energy gap of the keto and enol forms strongly support the occurrence of ESIPT in all the compounds (L1–L4). Furthermore, the presence of two different electron donating groups in L3 (triphenylamine and diethylamino) induced pH-dependent emissive features in solution.

45 citations