Protonation-Induced Chromism of Pyridylethynyl-Appended [core+exo]-Type Au₈ Clusters. Resonance-Coupled Electronic Perturbation through π-Conjugated Group

Abstract

A series of [core+exo]-type Au8 clusters bearing two alkynyl ligands on the exo gold atoms ([Au8(dppp)4(C≡CR)2](2+), 2-6) were synthesized by the reaction of [Au8(dppp)4](2+) (1) with alkynyl anions. Although the C≡C moieties directly attached to the Au8 units did not affect the optical properties arising from intracluster transitions, the pyridylethynyl-bearing clusters (4-6) exhibited reversible visible absorption and photoluminescence responses to protonation/deprotonation events of the terminal pyridyl moieties. The chromism behaviors and proton-binding constants of these clusters were highly dependent on the relative position of the pyridine nitrogen atom, such that the 2-pyridyl (4) and 4-pyridyl (6) isomers showed more pronounced responses than the 3-pyridyl isomer (5). These results suggest that the resonance-coupled movement of the positive charge upon protonation is involved in the optical responses, where the formation of extended charged resonance structures causes significant perturbation effects on the electronic properties of the Au8 unit and also contributes to the high binding affinities.

Phosphine-Coordinated Pure-Gold Clusters: Diverse Geometrical Structures and Unique Optical Properties/Responses

“…On the other hand, the core-to-exo distances are in the range 2.970 -3.072 Å, which are markedly longer than Au-Au distance in the bitetrahedral core (2.648 -2.872 Å). Other Au 6 +2Au type clusters (12 and 13) were reported recently [91,96], which show almost similar structural parameters (Table 4).…”

“…In addition, the alteration of nearby or external environments or physical stimuli could affect the optical properties, but such aspects have not been explored. We have recently found that the electronic perturbation coupled with $-conjugated system actually affects the optical properties of the cluster units [91]. As shown in Fig.…”

“…However, we recently found that the nucleophilic reaction towards [Au 8 (dppp) 4 ] 2+ (9) proceeds with the retention of the nuclearity but accompanies two-electron autoxidation and rearrangement of the cluster skeleton [91]. For instance, the reactions with nucleophiles such as halide and acetylide anions afford [Au 8 (dppp) 4 X 2 ]…”

Molecular and Electronic Structure of the Cluster [Au8(PPh3)8](NO3)2

“…The isolated and dried product was obtained in a yield of 392.6 mg (0.1 mmol, 74 %). 31 . 55339 reflections with indices -13 < h < 20, -21 < k < 21, -35 < l < 35 were collected in ω-scan mode in the range 2.19 < θ < 26.51°, an absorption correction (min.…”

Cluster–π electronic interaction in a superatomic Au13 cluster bearing σ-bonded acetylide ligands

“…15,16 We have also demonstrated a similar phenomenon for a structurally precise Au 8 cluster with an anisotropic core+exo-type structure. 17 Herein we report the first experimental evidence of electronic interaction between a polyhedral gold core and a σ-bonded π-unit in the absorption spectrum of a phenylethynyl-modified Au 13 cluster with an icosahedral geometry and superatomic 8-electron system. [19][20][21][22] We have also investigated its electronic structure based on DFT calculations, which support the presence of electronic interaction between the superatomic gold core and π-conjugated units.…”