Design and Synthesis of Fluorescent Carbon Dot Polymer and Deciphering Its Electronic Structure

Herein we report the one-pot synthesis of a fluorescent polymer-like material (pCD) by exploiting ruthenium-doped carbon dots (CDs) as building blocks. The unusual spectral profiles of pCDswith double-humped periodic excitation dependent photoluminescence (EDPL), and the regular changes in their corresponding average lifetime indicate the formation of high energy donor states and low energy aggregated states due to the overlap of molecular orbitals throughout the chemically switchable π-network of CDs on polymerization. To probe the electronic distribution of pCDs, we have investigated the occurrence of photoinduced electron transfer with a model electron acceptor, menadione using transient absorption technique, corroborated with low magnetic field, followed by identification of the transient radical ions generated through electron transfer. The experimentally obtained B_(1/2) value, a measure of the hyperfine interactions present in the system, indicates the presence of highly conjugated π-electron cloud in pCDs. The mechanism of formation of pCDs and the entire experimental findings have further been investigated through molecular modeling and computational modeling. The DFT calculations demonstrated probable electronic transitions from the surface moieties of pCDs to the tethered ligands

Formation of a gold-carbon dot nanocomposite with superior catalytic ability for the reduction of aromatic nitro groups in water

We report the synthesis of a gold-carbon dot nanocomposite and its utility as a recyclable catalyst for the reduction of aromatic nitro groups. The presence of carbon dots on gold nanosurfaces enhanced the reduction rate by two-fold

Design and Synthesis of Fluorescent Carbon Dot Polymer and Deciphering Its Electronic Structure

Herein we report the one-pot synthesis of a fluorescent polymer-like material (pCD) by exploiting ruthenium-doped carbon dots (CDs) as building blocks. The unusual spectral profiles of pCDswith double-humped periodic excitation dependent photoluminescence (EDPL), and the regular changes in their corresponding average lifetime indicate the formation of high energy donor states and low energy aggregated states due to the overlap of molecular orbitals throughout the chemically switchable π-network of CDs on polymerization. To probe the electronic distribution of pCDs, we have investigated the occurrence of photoinduced electron transfer with a model electron acceptor, menadione using transient absorption technique, corroborated with low magnetic field, followed by identification of the transient radical ions generated through electron transfer. The experimentally obtained B_(1/2) value, a measure of the hyperfine interactions present in the system, indicates the presence of highly conjugated π-electron cloud in pCDs. The mechanism of formation of pCDs and the entire experimental findings have further been investigated through molecular modeling and computational modeling. The DFT calculations demonstrated probable electronic transitions from the surface moieties of pCDs to the tethered ligands

Distance-Dependent Electron Transfer in Chemically Engineered Carbon Dots

The highly complex nanostructured framework of carbon dots (<b>CDs</b>) elevates scientific debates regarding their molecular and electronic structures. Here, we are able to highlight the free electron distribution on surface of newly synthesized Ru­(III) and amine (ethylenediamine) doped carbon nano dots, <b>Ru:CNDEDAs</b> by identifying <b>CD</b>^<b>+•</b> radical ions produced through photoinduced electron transfer to a model quinone drug, menadione (<b>MQ</b>) using laser flash photolysis corroborated with magnetic field of the order of 0.08 T. Amine passivation renders <b>Ru:CNDEDAs</b> surface to be a potential electron donor, which exhibits distance-dependent rapid electron transfer with <b>MQ</b> by chemical engineering with homocystein thiolactone (<b>HCTL</b>) in physiological condition. This modification is basically executed to mimic the post-translational modification (homocysteinylation) of protein–lysine residues by <b>HCTL</b>. Moreover, the high values of hyperfine splitting constants of <b>CD</b>s calculated from the magnetic field effect indicate the presence of excess conjugated π-electrons and heteroatoms within <b>CDs</b>

Metamorphosis of Ruthenium-Doped Carbon Dots: In Search of the Origin of Photoluminescence and Beyond

Carbon dots (CDs) are known to have a wide range of applications, yet our understanding of their structures and chemistry remains uncertain because of their highly complex nanostructured framework. Here we attempt to elucidate the molecular structure and intrinsic mechanisms governing photoluminescence (PL) of CDs by trapping seven visibly distinct colored intermediates that evolved during pyrolytic metamorphosis of citric acid with dopant Ru­(III). The “excitation-dependent” PL of doped CDs, Ru:CDs, can be tuned by ethylenediamine (EDA), yielding “excitation-independent” highly fluorescent nanodots, Ru:CNDEDAs. To mimic the optical and chemical properties of CDs, we devise a unique model cocktail comprising multiple fluorogenic molecules that truly supports the existence of chemically switchable conjugated moieties in CDs. We propose a plausible molecular level framework of CDs on the basis of spectroscopic findings and existing literature regarding thermal decomposition of CA. The PL of chemically engineered Ru:CNDEDAs is quenched efficiently by photoinduced electron transfer (PET) phenomenon. By exploiting the PET process, we also develop an important sensing platform for quantifying toxic and carcinogenic quinone derivatives in live HeLa cells that can be used for drug screening. Moreover, the distribution pattern of these photoluminiscent nanodots in HeLa cells is studied to demonstrate their utilities as endosomal markers

Development of Decadal (1985–1995–2005) Land Use and Land Cover Database for India

India has experienced significant Land-Use and Land-Cover Change (LULCC) over the past few decades. In this context, careful observation and mapping of LULCC using satellite data of high to medium spatial resolution is crucial for understanding the long-term usage patterns of natural resources and facilitating sustainable management to plan, monitor and evaluate development. The present study utilizes the satellite images to generate national level LULC maps at decadal intervals for 1985, 1995 and 2005 using onscreen visual interpretation techniques with minimum mapping unit of 2.5 hectares. These maps follow the classification scheme of the International Geosphere Biosphere Programme (IGBP) to ensure compatibility with other global/regional LULC datasets for comparison and integration. Our LULC maps with more than 90% overall accuracy highlight the changes prominent at regional level, i.e., loss of forest cover in central and northeast India, increase of cropland area in Western India, growth of peri-urban area, and relative increase in plantations. We also found spatial correlation between the cropping area and precipitation, which in turn confirms the monsoon dependent agriculture system in the country. On comparison with the existing global LULC products (GlobCover and MODIS), it can be concluded that our dataset has captured the maximum cumulative patch diversity frequency indicating the detailed representation that can be attributed to the on-screen visual interpretation technique. Comparisons with global LULC products (GlobCover and MODIS) show that our dataset captures maximum landscape diversity, which is partly attributable to the on-screen visual interpretation techniques. We advocate the utility of this database for national and regional studies on land dynamics and climate change research. The database would be updated to 2015 as a continuing effort of this study