Computational Study of the Influence of the Binding Geometries of Organic Ligands on the Photoluminescence Quantum Yield of CdSe Clusters

Abstract

This article describes density-functional-theory- (DFT-) based calculations of the rate constants for radiative (k R) and nonradiative (k NR) decay from the lowest singlet excited state (S1) to the ground state (S0) of a Cd16Se13 cluster ligated with various molecules in various binding geometries. The value of k R is suppressed by ligands whose localized orbitals, as a result of their binding geometry, become the cluster’s frontier orbitals and, thereby, decrease the overlap of the electron densities of the HOMO and LUMO necessary for efficient dipole coupling. Thiolate ligands in a monodentate geometry and dithioate ligands in a bridging geometry decrease k R in this manner. The value of k NR is also sensitive to the binding geometries of the ligands: binding geometries that are less rigid yield a greater change in nuclear coordinates between the S1 and S0 electronic states, which, in turn, increases the rate of nonradiative decay by maximizing the vibronic coupling between the band-edge exciton and the vibrational modes of the ligands. This work suggests that the photoluminescence quantum yield of CdSe nanoparticles can be maximized by ensuring that the bridging binding mode is the dominant binding mode of the ligands; bridging modes decrease the nonradiative decay rate and eliminate mid-band-gap trap states in all cases studied, except for dithioate ligands.

Resonance Raman Vibrational Mode Enhancement of Adsorbed Benzenethiols on CdSe Is Predominantly Franck–Condon in Nature and Governed by Symmetry

“…Bound ligands with C s symmetry had totally symmetric 8b modes which were resonantly enhanced, whereas the same effect was not observed in the case of 4-MBT in which the 8b mode is nontotally symmetric and therefore not enhanced. These experimental observations corroborate previously reported computational results as well as similar experiments involving SERS with metallic nanoparticles. ,, The results provided in this work should provide a starting basis for more complex Raman studies involving excitation, temperature, and polarization dependence. The results presented herein demonstrate that resonance Raman spectroscopy can be used to answer fundamental questions regarding excitonic coupling to ligand vibrations in NCs.…”

“…The proposed mechanisms in which ligand vibrations couple to excitonic transitions in II–VI NCs have not yet been experimentally verified. − Methods to study such couplings include sum-frequency generation, infrared-pump electronic probe, and resonance Raman (RR) spectroscopies. , Methodologies allowing for the observation of RR signal enhancements of chemisorbed ligands on the surface of colloidal semiconductor nanocrystals (NCs) have recently been demonstrated by our group and others. ,,− While the origin of the signal enhancements in these works was suggested to be consistent with the charge-transfer (CT) theory of surface enhanced Raman scattering (SERS), this present work goes further in experimentally testing such predictions . As exciton-ligand coupling can have a direct impact on the resulting optoelectronic properties of NCs, obtaining a thorough knowledge of these fundamental interactions is essential in order to effectively design NCs with impressive optoelectronic properties.…”

Radiative lifetime of a BODIPY dye as calculated by TDDFT and EOM-CCSD methods: solvent and vibronic effects

“…First principle calculations of quantum yields for different dyes were reported in the literature. [38][39][40][41][42][43][44][45][46][47] In most studies, the radiative rate was estimated from the Einstein coefficient by assuming a two states approximation involving only the electronic parts of the ground and first excited states. In a few cases (e.g.…”

Effects of Aromatic Thiol Capping Agents on the Structural and Electronic Properties of CdnTen (n = 6,8 and 9) Quantum Dots

“…On the other hand, first-principles computational techniques have been a good instrument for investigating the structures and properties of QDs. The cluster models have been used in several theoretical studies to investigate the structural and electronic properties of bare and ligated CdSe/ CdTe QDs (Bhattacharya and Kshirsagar, 2007;Bhattacharya and Kshirsagar, 2008;Wang et al, 2009;Xu et al, 2010a;Seal et al, 2010;Haram et al, 2011;Kuznetsov et al, 2012;Lim et al, 2012;Ma et al, 2012;Leubner et al, 2013;Lin et al, 2013;Sriram and Chandiramouli, 2013;Wu et al, 2013;Alnemrat et al, 2014;Kuznetsov and Beratan, 2014;Rajbanshi et al, 2014;Sarkar et al, 2014;Shah and Roy, 2014;Aruda et al, 2016;Kilina et al, 2016;Swenson et al, 2016;Cao et al, 2018). Mainly, these studies were limited to exploring the capping effects of aliphatic ligands on the structural, electronic, and optical properties of CdTe QDs.…”

“…Recent computational and experimental studies have confirmed the utilization of aromatic capping ligands in synthesis and the capping exchange process of CdSe/CdTe QDs (Bloom et al, 2013;Lin et al, 2013;Kumar et al, 2015;Aruda et al, 2016;Swenson et al, 2016). However, significant and systematic studies that would have investigated the effect of aromatic ligands on the structural, electronic, and optical properties of CdTe QDs are rare.…”