Faculty Publications

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Highly fluorescent materials derived from ortho-vanillin: Structural, photophysical electrochemical and theoretical studies
(Elsevier B.V., 2019) Poojary, S.; Acharya, M.; Abdul Salam, A.A.; Kekuda, D.; Nayek, U.; Madan Kumar, S.; Vasudeva Adhikari, A.V.; Dhanya, D.
Small-molecule organic fluorophores are highly in demand attributed to their extensive prospective in material and biomedical applications. Particularly, luminescent ?-conjugated organic molecules that possess an efficient solid-state emission are excellent candidates for optoelectronic devices. Focusing on high demand of organic fluorophores, we herein report the synthesis of three organic fluorescent materials derived from o?vanillin, viz. an ester (F1), an azine (F2) and an azo dye (F3). Interestingly, F2 exhibited very intense luminescence in its aggregate phase due to the restriction in intra-molecular rotation (RIR), as demonstrated by solution thickening studies. Further, its Single Crystal X-ray Crystallography (SCXRD) study suggested the existence of various intra and inter molecular interactions and gave evidences for locked intra-molecular rotations of the benzene rings in the rigid conformation of the molecule. The bathochromic shift in fluorescence from solution to solid phase was confirmed by its thin-film emission spectrum, which evidences the formation of J-aggregates. The observed RIR, development of J-aggregates and high conjugation in F2 impart an excellent fluorescence in its aggregated state. Thin films of both F2 and F3 on ITO plates exhibited a bathochromic shift with a deep orange to red photoluminescence on UV excitation. Furthermore, the morphological characterization revealed the presence of clear dense grains in case of F2 and F3, while the DSC analysis indicated phase transitions of all the derivatives. As seen from dielectric measurement studies, the azo dye F3 exhibited the highest dielectric constant among the three derivatives. The electronic and photophysical data based on Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) calculations are in agreement with the experimental results. All the above data clearly advocate that, the synthesized fluorophoric o?vanillin derivatives are excellent candidates for electro-optical devices. © 2018 Elsevier B.V.
Orthovanillin azine ester as a potential functional material for organic electronic devices
(Elsevier B.V., 2023) Kagatikar, S.; Acharya, S.; Mp, Y.; Dhanya, D.; Kekuda, D.; Abdul Salam, A.A.; Sudhakar, S.N.; Mn, S.; De, S.
The present study reports the synthesis of OVAE, an ester of ortho-vanillin azine, and its structural characterization using spectral and single crystal-XRD studies. Intermolecular interactions of OVAE are investigated using the Hirshfield surface analysis, 3D Hirshfield surface maps, 2D fingerprint plots, and electrostatic energy frameworks. Good thermal stability in thermogravimetric analysis, irreversible redox peaks in electrochemical studies, high carrier concentration and dielectric constant in electrical measurements, uniform films observed upon surface morphology examination, fabrication of a diode, the obtained current-voltage characteristics, dielectric constant and frequency-dependent AC conductivities directed towards the use of OVAE as a potential semiconducting functional material in suitable electronic devices. Based on cyclic voltammetry and AC impedance response, the performance of OVAE as an electrode material is explored by constructing a supercapacitor, which exhibited a specific capacitance of 56 Fg−1 at 10 mV s−1. © 2023 Elsevier B.V.
Investigation of column purified dye derived carbon nanomaterials for security printing and supercapacitor applications
(Elsevier B.V., 2024) Mehta, R.; Ullal, N.; Sahoo, B.; Dhanya, D.; Kulkarni, S.D.; Sudhakar, Y.N.; Abdul Salam, A.A.; K, U.B.; Anand, P.J.
Literature evidence reveals versatile applications of carbon dots (CDs), but generally mixtures of various types of carbon nanomaterials, molecular intermediates as well as side products are obtained upon hydrothermal treatment of the precursor material. This demands isolation of pure components and their complete characterization before these nano carbonaceous materials are chosen for suitable applications. In the present study, perylenetetracarboxylic dianhydride (PTCDA) is subjected to hydrothermal treatment and the mother liquor obtained is separated using column chromatography technique using dichloromethane-methanol solvent system to isolate fractions of various fluorescent carbonaceous nanostructures. The TEM imaging of nano carbonaceous particles of all five fractions indicated that the first and third fractions were composed of nanoribbons, while the latter two fractions largely contained quasi-spherical nanoparticles of both lesser (carbon quantum dots) and greater (carbon nanodots) than 10 nm dimensions. The XPS results of all the fractions suggested separation based on polarity difference. The ID/IG ratios obtained from Raman spectra implied the presence of several defects on the CDs. The time resolved fluorescence spectra of third, fourth and fifth fractions revealed mono-exponential decay of fluorophores with excitation independent average lifetime values. The fifth fraction exhibited good biocompatibility and the highest absolute fluorescence quantum yield of 58.47 % among all the isolated samples. As these CDs displayed a remarkable rise in the quantum yield to 88.60 % when dispersed in water, a water-based flexo-ink was formulated. The photostable pale yellow flexo print proofs obtained on UV dull paper exhibited a green fluorescence under 365 nm illumination, whereas a yellow glow when shined with blue light, which can serve as an authentication feature for security documents and currency notes. Moreover, as the third fraction constitutes mainly of carbon nanoribbons (CNRs), an optimized polymer electrolyte was prepared along with sodium alginate (SA), and MgCl2 to understand their potential use in energy storage application. A supercapacitor was fabricated and tested for its electrochemical performance such as cyclic voltammtery (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCD). An enhanced current window was observed in the CV of SA/CNRs compared to pure SA and SA/CNRs/Mg films, which indicated a structural interaction of CNRs with SA. The conductivity of SA/CNRs/Mg was lesser than SA/CNRs in EIS studies due to the presence of Mg ions, while pure SA showed lesser conductivity. The dual ionic interaction of Na and Mg along with enhanced structural stability due to doped CNRs favors its convenient supercapacitor application. The fabricated eco-friendly supercapacitor showed a specific capacitance of 84 F/g. The GCD of the device displayed pseudocapacitance behaviour and was quite stable for 2000 cycles with coulombic efficiency of 96 %. © 2024 The Author(s)

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