Photophysical and Redox Properties of Molecule-like CdSe Nanoclusters

Abstract

Advancing our understanding of the photophysical and electrochemical properties of semiconductor nanoclusters with a molecule-like HOMO-LUMO energy level will help lead to their application in photovoltaic devices and photocatalysts. Here we describe an approach to the synthesis and isolation of molecule-like CdSe nanoclusters, which displayed sharp transitions at 347 nm (3.57 eV) and 362 nm (3.43 eV) in the optical spectrum with a lower energy band extinction coefficient of ~121,000 M(-1) cm(-1). Mass spectrometry showed a single nanocluster molecular weight of 8502. From this mass and various spectroscopic analyses, the nanoclusters are determined to be of the single molecular composition Cd34Se20(SPh)28, which is a new nonstiochiometric nanocluster. Their reversible electrochemical band gap determined in Bu4NPF6/CH3CN was found to be 4.0 V. There was a 0.57 eV Coulombic interaction energy of the electron-hole pair involved. The scan rate dependent electrochemistry suggested diffusion-limited transport of nanoclusters to the electrode. The nanocluster diffusion coefficient (D = 5.4 × 10 (-4) cm(2)/s) in acetonitrile solution was determined from cyclic voltammetry, which suggested Cd34Se20(SPh)28 acts as a multielectron donor or acceptor. We also present a working model of the energy level structure of the newly discovered nanocluster based on its photophysical and redox properties.

Luminescent CdSe Superstructures: A Nanocluster Superlattice and a Nanoporous Crystal

“…CdSe nanoparticles (average diameter ∼4 nm) with phenylchalcogenolate ligands were also previously reported to show broad long-lived trapped emission at 77 K while no emission at room temperature; in the latter case relaxation was assigned to a combination of hole transfer to the ligand (more efficient at higher temperature and for the ligands in the row PhS – < PhSe – < PhTe – ) and of phonon-assisted nonradiative decay pathways . In contrast, room temperature trapped emission (broad band at 604 nm) was reported for much smaller CdSe nanoparticles with thiophenolate ligands . Generally, a complex relationship among nanocluster/nanoparticle size, shape, surface structure and relaxation pathways in the system may exist; the surface science of nanoscale objects represents the area of active scientific research where many phenomena are still far from being fully understood .…”

Dual Role of Electron-Accepting Metal-Carboxylate Ligands: Reversible Expansion of Exciton Delocalization and Passivation of Nonradiative Trap-States in Molecule-like CdSe Nanocrystals

“…Figure shows the time-dependent 1 H NMR spectra of the aromatic ortho proton signals of Cd­(O 2 CPh) 2 at 8.12 ppm after TMEDA treatment. The broad aromatic signal, which appears from a combination of spin–spin relaxation and dipole broadening, ,, becomes sharper and increases in intensity. Our experimental result is in agreement with a previous report demonstrating removal of Z-type ligands from the surface of CdSe nanocrystals upon treatment with L-type ligands .…”

Investigating the Control by Quantum Confinement and Surface Ligand Coating of Photocatalytic Efficiency in Chalcopyrite Copper Indium Diselenide Nanocrystals

“…This demonstrates the importance of surface ligand coating: appropriate ligands enable measurements in electrochemically suitable solvent/electrolyte systems as shown in the present investigation. Thus, electrochemical techniques could obviate the need for expensive spectroscopic techniques commonly used to determine the band gap and HOMO and LUMO position of semiconductor NCs. , Finally, similar to thiolate-protected gold nanoparticles and CdSe and InAs QDs, we also developed a basic energy level diagram (Figure C) of PEG 6 -thiolate-coated 1.8 nm diameter CuInSe 2 NCs from UV–vis and PL spectroscopic and CV characterizations.…”