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Ultrafast Relaxation Dynamics of Luminescent Copper Nanoclusters (CuL) and Efficient Electron Transfer to Functionalized Reduced Graphene Oxide Subarna Maity, Dipankar Bain, Kalishankar Bhattacharyya, Soma Das, Rajesh Bera, Bikash Jana, Bipattaran Paramanik, Ayan Datta, and Amitava Patra J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b09959 • Publication Date (Web): 29 Nov 2017 Downloaded from http://pubs.acs.org on December 5, 2017
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The Journal of Physical Chemistry
Ultrafast Relaxation Dynamics of Luminescent Copper Nanoclusters (Cu7L3) and Efficient Electron Transfer to Functionalized Reduced Graphene Oxide Subarna Maity†, Dipankar Bain†, Kalishankar Bhattacharyya‡, Soma Das†, Rajesh Bera†, Bikash Jana†, Bipattaran Paramanik#, Ayan Datta‡ and Amitava Patra†* †
Department of Materials Science, Indian Association for the Cultivation of Science, Kolkata
700 032, India ‡ Department of Spectroscopy, Indian Association for the Cultivation of Science, Jadavpur 700032, West Bengal, India
*
Author to whom correspondence should be addressed. Electronic mail:
[email protected] Telephone: (91)-33-2473-4971. Fax: (91)-33-2473 #Present address; Department of Chemistry, New Alipore College, Kolkata 700053, India
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ABSTRACT Luminescent copper nanoclusters (Cu NCs) have emerged as a fascinating nanomaterials for the potential applications in optoelectronics, catalysis and sensing. Here, we demonstrate the synthesis of L-cysteine capped Cu NCs in aqueous medium having a bright cyan emission (489 nm) with quantum yield of 6.2%. The structure of the Cu NCs (Cu7L3) is investigated by using Density functional theory (DFT) calculation and mass spectrometric study. Further, time dependent density functional theory (TD-DFT) calculations provide the insights of electronic transitions and it is correlated with experimental data. With near HOMO-LUMO gap excitation, Cu NCs are excited to S4 state and subsequently relaxed to S1 state through an internal conversion process with a time scale in ultrafast region (326.8 ± 6.5 fs). Furthermore, the structural relaxation in S1 takes place in picosecond time scale and the radiative relaxation occurs from S1 to S0. Finally, Cu NCs are attached with imidazole functionalized partially reduced graphene oxide (ImRGO) via electrostatic attraction. A dramatic photoluminescence (PL) quenching and shortening of decay time of Cu cluster in presence of ImRGO indicate the photoinduced electron transfer process which is confirmed from ultrafast spectroscopic study. The photoinduced electron transfer in Cu NC-ImRGO nanocomposite should pave the way for the potential applications in light harvesting.
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The Journal of Physical Chemistry
INTRODUCTION Fluorescent metal nanoclusters (MNCs) consisting of several to hundreds of metal atoms have emerged as a frontier area of nano-research for their wide applications in optoelectronics, bioimaging, catalysis and sensing.1-6 In recent days, luminescent MNCs are considered as the alternatives to semiconductor quantum dots, organic fluorophores and fluorescent protein molecules due to their ultra small size, high quantum yield, excellent photo stability and good biocompatibility.7-11 Unlike metal nanoparticles (NPs), nanoclusters having diameter
