• K George Thomas

      Articles written in Journal of Chemical Sciences

    • Photosensitizing properties of squaraine dyes

      Suresh Das K George Thomas Prashant V Kamat M V George

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      The present report summarises our results on the photophysical and photochemical investigations of a series of squaraine dyes which exhibit intense and sharp absorption bands in the visible and near infrared regions. The intramolecular charge-transfer transitions arising from the “donor-acceptor-donor” arrangements of these dyes have an interesting effect on their excited state properties. The major nonradiative decay process of squaraines is by rotation about the C-C bonds between the central cyclobutane unit and its neighbouring phenyl groups. Microencaging of one of the dyes by Β-cyclodextrin or poly(4-vinylpyridine) was found to restrict this motion, bringing about up to 90-fold enhancement in its fluorescence yield. These aspects as well as the dynamics of charge transfer from the excited singlet state of some of the squaraine dyes to TiO2 and the recombination of the injected charge with the dye radical cation are discussed.

    • Cation binding and photophysical properties of a monoaza-15-crown-5-ether linked cyanine dye

      K J Thomas K George Thomas T K Manojkumar Suresh Das M V George

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      A cyanine chromoionophore1 has been synthesised and its photophysical properties have been investigated. Complexation with alkali metal cations (Li+ and Na+) brings about a significant shift in the absorption and emission spectra to shorter wavelengths, which is accompanied by an enhancement in the fluorescence quantum yield. These effects can be attributed to the suppression of intramolecular charge transfer processes of the cyanine dye, brought about by complexation with the metal cations.

    • Rigid rod spaced fullerene as building block for nanoclusters

      Pallikara K Sudeep James P Varkey K George Thomas Manappurathu V George Prashant V Kamat

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      By using phenylacetylene based rigid-rod linkers (PhA), we have successfully synthesized two fullerene derivatives, C60-PhA and C60-PhA-C60.The absorption spectral features of C60, as well as that of the phenylacetylene moiety are retained in the monomeric forms of these fullerene derivatives, ruling out the possibility of any strong interaction between the two chromophores in the ground state. Both the fullerene derivatives form optically transparent clusters, absorbing in the UV-Vis region; this clustering leads to a significant increase in their molar extinction coefficients. TEM characterization of the C60-PhA showed large spherical clusters, with sizes ranging from 150–350 nm, while an elongated wire-type structure was observed for the bisfullerene derivative (C60-PhA-C60).AFM section analysis studies of isolated nanoclusters of C60-PhA-C60, deposited on mica, indicate that smaller clusters associate to form larger nanostructures.

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