BITS Faculty Publications

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Subject: search.filters.subject.Fluorophores

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    Deciphering the Photophysical Role of Conjugated Diyne in Butadiynyl Fluorophores: Synthesis, Photophysical and Theoretical Study
    (ACS, 2013-07) Pati, Avik K.
    The present work focuses on the current interest in diyne bridged chromophores necessitating a clearer understanding of the photophysics of such molecules. The significance of the diyne moiety in the photophysics has been investigated by synthesizing simple substituted diphenyl butadiynyl derivatives following a quick and efficient microwave assisted Eglinton coupling of terminal alkynes. Emission of the fluorophores is observed from the usual locally excited (LE) state and intramolecular charge transfer (ICT) state. Separation of pure ICT emission from pure LE emission has been carried out by Gaussian/Lorentzian curve fitting. The vibronic coupling in the local transitions appears to be confined to the normal mode involving the C–C triple bond stretching of the diyne moiety. This implies that the LE transition involves the diyne moiety, a conclusion supported by quantum chemical calculations. The resolved ICT emission follows double linear dependence on ET(30) solvent polarity scale. The important role of the diyne moiety in the photophysics of this class of molecules is clearly discernible in this study.
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    Small push-pull diacetylenes as emergent fluorophores
    (AIP, 2018-08) Pati, Avik K.
    Organic fluorophores containing acetylene spacers have gained significant current interest because of their wide-spread applications in optoelectronics. In this present review, we summarize our recent photophysical understanding on small organic dyes which contain a diacetylene conduit. Diphenylbutadiynes with push-pull substituents exhibited emissions from both locally excited (LE) and intramolecular (ICT) states in non-aqueous media. The LE emission was confined to the normal mode involving C≡C stretching of the diacetylene moiety. Quantum chemical calculations showed that the fluorophores are twisted and the diyne moiety deviates from the usual linearity (sp) in the ICT excited state. The diphenylbutadiynes with an acceptor group at meta position of the phenyl ring produced the lowest absorption energy compared to their ortho and para isomers, which was related to the ‘meta effect’ well-known in organic photochemical reaction. The ‘meta effect’ was not perceived when the chain length (n) was increased (n≥4). Butadiyne bridged pyrene-phenyl hybrid derivatives showed the LE emission originating from the pyrene core, which was in contrast to the observation of the LE emission in the diphenylbutadiynes. The dyes showed aggregate emission in mixed-aqueous solvents. In addition to the solution state emission, the fluorophores exhibited emission in solid powder form and showed reversible fluorescence switching in the solids. The solid state emission of the derivatives was either blue (excitonic coupling) or red (excimeric coupling) shifted with regard to the solution phase emission spectrum, depending on the size of the peripheral aromatic moiety. The diynes containing donor and acceptor peripheries displayed single component white light emission, which was exploited to polar aprotic vapor detection in a polymer film matrix. The photophysical outcomes of the diacetylenic dyes make them a promising class of important π-conjugated organic fluorophores.
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    Tuning the Baird aromatic triplet-state energy of cyclooctatetraene to maximize the self-healing mechanism in organic fluorophores
    (PNAS, 2020-09) Pati, Avik K.
    Bright, photostable, and nontoxic fluorescent contrast agents are critical for biological imaging. “Self-healing” dyes, in which triplet states are intramolecularly quenched, enable fluorescence imaging by increasing fluorophore brightness and longevity, while simultaneously reducing the generation of reactive oxygen species that promote phototoxicity. Here, we systematically examine the self-healing mechanism in cyanine-class organic fluorophores spanning the visible spectrum. We show that the Baird aromatic triplet-state energy of cyclooctatetraene can be physically altered to achieve order of magnitude enhancements in fluorophore brightness and signal-to-noise ratio in both the presence and absence of oxygen. We leverage these advances to achieve direct measurements of large-scale conformational dynamics within single molecules at submillisecond resolution using wide-field illumination and camera-based detection methods. These findings demonstrate the capacity to image functionally relevant conformational processes in biological systems in the kilohertz regime at physiological oxygen concentrations and shed important light on the multivariate parameters critical to self-healing organic fluorophore design.
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    One-Pot Synthesis of Vinylogous Cyano Aminoaryls (VinCAs) as Benzenic Fluorophores: Tailoring Diverse Emission Colors for White Light Emitting Materials and Cell Imaging
    (ACS, 2024-05) Ghosh, Sarbani; Chowdhury, Rajdeep; Addy, Partha Sarathi
    Donor–acceptor-based organic small molecules with an electronic push–pull effect can demonstrate intramolecular charge transfer to show interesting photoluminescence properties. This is an essential criterion for designing fluorogenic probes for cell imaging studies and the development of organic light-emitting diodes. Now, to design such optical materials sometimes it is necessary to tune the band gap by controlling the energies of the highest occupied molecular orbital and lowest unoccupied molecular orbital. Typically, the band gaps could be modulated by installing unsaturated handles between electron-rich donors and electron-deficient acceptors. However, these methods are often synthetically and economically challenging due to the involvement of expensive catalysts and difficult reaction setups. In our present study, we show a straightforward, cost-effective method for obtaining a series of donor–acceptor-type Vinylogous Cyano Aminoaryls (VinCAs) with diverse emission colors. Further studies reveal that these VinCAs can serve as effective cell imaging agents, showcasing potential use in chemical biology. Additionally, these molecules could be further used to generate white light emission (WLE), showing their potential utility in advanced lighting technologies
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    Trends in small organic fluorescent scaffolds for detection of oxidoreductase
    (Elsevier, 2021-11) Sidhu, Jagpreet Singh
    Oxidoreductases are diverse class of enzymes engaged in modulating the redox homeostasis and cellular signaling cascades. Abnormal expression of oxidoreductases including thioredoxin reductase, azoreductase, cytochrome oxidoreductase, tyrosinase and monoamine oxidase leads to the initiation of numerous disorders. Thus, enzymes are the promising biomarkers of the diseased cells and their accurate detection has utmost significance for clinical diagnosis. The detection method must be extremely selective, sensitive easy to use, long self-life, mass manufacturable and disposable. Fluorescence assay approach has been developed potential substitute to conventional techniques used in enzyme's quantification. The fluorescent probes possess excellent stability, high spatiotemporal ratio and reproducibility represent applications in real sample analysis. Therefore, the enzymatic transformations have been monitored by small activatable organic fluorescent probes. These probes are generally integrated with enzyme's substrate/inhibitors to improve their binding affinity toward the enzyme's catalytic site. As the recognition unit bio catalyzed, the signaling unit produces the readout signals and provides novel insights to understand the biochemical reactions for diagnosis and development of point of care devices. Several structural modifications are required in fluorogenic scaffolds to tune the selectivity for a particular enzyme. Hence, the fluorescent probes with their structural features and enzymatic reaction mechanism of oxidoreductase are the key points discussed in this review. The basic strategies to detect each enzyme are discussed. The selectivity, sensitivity and real-time applications are critically compared. The kinetic parameters and futuristic opportunities are present, which would be enormous benefits for chemists and biologists to understand the facts to design and develop unique fluorophore molecules for clinical applications.