Enhancement of External Spin−Orbit Coupling Effects Caused by Metal−Metal Cooperativity

Abstract

As part of our efforts to discover simple routes to room-temperature phosphors, we have investigated the interaction of bis(pentafluorophenyl)mercury (1) or trimeric perfluoro-o-phenylene mercury (2) with selected arenes (naphthalene, biphenyl, and fluorene). Solution studies indicate that 2, unlike 1, quenches the fluorescence of naphthalene. When compared to 1, the high quenching efficiency of 2 may be correlated to the higher affinity that 2 displays for arenes as well as to more acute external heavy-atom effects caused by the three mercury atoms. In the crystal, the adducts [1.naphthalene], [1.biphenyl], [1.fluorene], and [2.fluorene] form supramolecular binary stacks in which the arene approaches the mercury centers of 1 or 2 to form Hg-C pi-interactions. Analysis of the electrostatic potential surfaces of the individual components supports the involvement of electrostatic interactions. The luminescence spectra of the adducts show complete quenching of the fluorescence and display heavy-atom-induced emission whose energies and vibronic progressions correspond to the phosphorescence of the respective pure arene. The phosphorescence lifetimes are shortened by 3 or 4 orders of magnitude when compared with those of the free arenes. Taken collectively, the structural, photophysical, and computational results herein suggest that the proximity of the three mercury centers serves to enhance the Lewis acidity of 2, which becomes a better acceptor and a more effective heavy-atom effect inducer than 1.

Phosphorescence sensitization via heavy-atom effects in d10 complexes

“…2). Incremental addition of trimer 1 resulted in the quenching of the arene fluorescence as an indication of molecular interaction in solution [7]. Stern-Volmer analysis [10] yielded a formation constants (K sv ) of 159 ± 6 M -1 for the naphthalene adduct of 1, as shown in Fig.…”

“…New adducts have been synthesized which contain an organic aromatic (arene) component and a heavy-metal inorganic component with an opposite p acid-base or donor-acceptor character [4][5][6][7][8][9]. The resulting adducts exhibit sensitized phosphorescence characteristic of the organic aromatic component owing to external HAE of the heavy-metal component in the vicinity of the arene.…”

“…Stern-Volmer analysis [10] yielded a formation constants (K sv ) of 159 ± 6 M -1 for the naphthalene adduct of 1, as shown in Fig. 2 [7]. For biphenyl and fluorene, fluorescence quenching experiments could not be carried out because of a large overlap between the absorption spectrum of the mercury trimer quencher and the excitation spectrum of the arene.…”

Halogen Bonding in the Design of Organic Phosphors

“…In group two, the bonding distances are 3.411, 3.655, 3.613, 3.487, and 3.536 Å, with bonding angles of 170. 6 , 148.3 , 159.5 , 170.4 , and 158.8 , respectively. If a dibenzothiophene molecule is given a reversed orientation, the bonding distances and bonding angles in the sequentially resulting cocrystal structure are the same as the original ones.…”

“…When metal ions coordinate luminescent organic ligands, the extrinsic heavy atom effect may become more efficient, e.g., when Ag(I) interacts with polyaromatic hydrocarbons by Ag-π complexation or Hg(II) with N-heterocyclic aromatic hydrocarbons by Hg-N bonding [4,5]. Metal ions can sometimes act as intrinsic or a special heavy atom effect between extrinsic and intrinsic by complexation or coordination with phosphor as chelator with exact stoichiometry, corresponding to directly or indirectly acting on a luminescent central group of organic molecules [6][7][8].…”