Fluorescent Carbon Nanoparticles: Prospects in Excited State Dynamics

Mondal, Somen (2016) Fluorescent Carbon Nanoparticles: Prospects in Excited State Dynamics. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

As new members of carbon material family, carbon nanoparticles (CNPs) have attracted tremendous attentions for their potential biological, photo and electron-properties and energy related applications. Among these applications, photo and electron-properties of the CNPs are on principal focus of my research. My research work gives an overview of electron acceptor and donor properties of photoexcited CNPs. In Chapter I, a brief outline on different photophysical process has been given and also an introduction of CNPs. In chapter II and III have been described scope of the thesis and the details of experiments respectively. In chapter IV has demonstrated novel and simpler approaches to generate and characterise core–shell type surfactant bilayer coated CNPs. Thickness of bilayer around CNPs were characterised using FRET as a tool through a strategic choice of fluorescent dyes.( phenosafranine (PSF), a cationic dye, and fluorescein (FL), an anionic dye). The calculated FRET efficiencies help to estimate the thickness of various zones of the surfactant bilayer shell in a precise way. Applications of these core–shell CNP surfactant systems were attempted to control photoinduced electron transfer (PET) that can be tuned by changing the thickness of the surfactant shell surrounding the CNP aggregates. The work reported in Chapter V has shown the use of cyclometalated inorganic complexes of Rh and Ir in PET with fluorescent CNPs in acetone medium, wherefrom it was observed that the heterometallic complex of Ir-Rh is the most promising quencher due to its redox asymmetry. Working more in the area of PET, in chapter VI, the CNPs were confined in reverse micelles (RMs) where a synergistic effect was noticed on the rate of PET on combining with an electron donor compound, dimethylaniline (DMA) and an electron acceptor, methyl viologen (MV2+). CNPs and the electron donor DMA are captured in the nonpolar environment of the RMs while MV2+, the electron acceptor, readily goes into the water pool and character of the reverse micelles decides the kinetics of PET. In chapter VII, a new class of surface modified dopamine functionalized CNPs was developed that can act as efficient electron donor as well as acceptor depending on the pH of the medium. Thus a reversible PET to and from dopamine modified CNPs are possible only by triggering the pH of the medium. Finally, in chapter VIII, a host−guest approach was adopted to build a nanoscale assembly of α-CD-CNPs and different derivatives of MV2+ as electron acceptors. A nanotubular aggregates is produced in between α-CD-CNPs and 1,1′-diheptyl-4,4′-bipyridinium dibromide (DHMV2+) and these aggregates enhance the efficiency of PET and increases the rate of electron transfer. The results obtained from the above studies were not only encouraging but also helped to open new areas of investigation to control PET and tune it to use in energy conservation and conversion.

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