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Electron Donating Chlorophyll‑a on Graphene: A Way toward Tuning Fermi Velocity in an Extended Molecular Framework of Graphene/Chlorophyll‑a Nanohybrid

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journal contribution
posted on 02.04.2015, 00:00 by Debmallya Das, Jhimli Sarkar Manna, Manoj K. Mitra
We aimed to synthesize graphene/chlorophyll-a nanohybrids with an extended interface via the LB method, through which charge and energy-transfer processes can create synergistic effects resulting in unique properties and superior performance with regard to photovoltaic and advanced electronics applications. The reduced lifetime of excited-state chlorophyll-a molecules, evident from time-resolved fluorescence decay (TCSPS) data, is accounted for by the effect of two phenomena that are intermolecular exciton migration through packed chlorophyll-a molecules [radiative] and electron transfer from chlorophyll-a to the graphene surface [nonradiative]. The G band in the Raman spectra gradually shifts to lower frequency with decreasing layer numbers, implying electron transfer from porphyrin to graphene is prominent due to the doping induced change of the equilibrium lattice parameter along with nonadiabatic removal of the Kohn anomaly. The lattice relaxation effect is also evident from the decrease in symmetric 2D band intensity with increased electron concentration over the graphene surface. The photophysical properties of the nanohybrid in addition to the structural analysis focus how a combination of the unique molecular structure and colloidal interactions can lead to simple, solution-phase approaches for exfoliating graphene into a nanohybrid architecture to offer exciting functions, suitable for an artificial antenna complex and next generation electronics. The specific correlation between the chlorophyll-a modification scheme of the graphene and their novel tunable material properties is evaluated through scanning tunneling spectroscopy, which shows increased electron density and reduced Fermi velocity, revealing that chlorophyll-a can effectively tune the graphene density of state by introducing corrugation through π-stacking, leading to the appearance of the Van Hove singularity. This graphene/chlorophyll-a nanohybrid can be highly functional in advanced molecular electronics.

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