Structures, Photoluminescence, and Reversible Vapoluminescence Properties of Neutral Platinum(II) Complexes Containing Extended π-Conjugated Cyclometalated Ligands

Abstract

Reacting K2PtCl4 with the tridentate R-C(wedge)N(wedge)C-H2 ligands 2,6-di-(2'-naphthyl)-4-R-pyridine (R = H, 1a; Ph, 1b; 4-BrC6H4, 1c; 3,5-F2C6H3, 1d) in glacial acetic acid, followed by heating in dimethyl sulfoxide (DMSO), gave complexes [(R-C(wedge)N(wedge)C)Pt(DMSO)] (2a-d). In the crystal structures of 2a-c, the molecules are paired in a head-to-tail orientation with Pt...Pt separations >6.3 A, and there are extensive close C-H...pi (d = 2.656-2.891 A), pi...pi (d = 3.322-3.399 A), and C-H...O=S (d = 2.265-2.643 A) contacts. [(Ph-C(wedge)N(wedge)C)Pt(PPh3)] (3) was prepared by reacting 2b with PPh3. Reactions of 2a-d with bis(diphenylphosphino)methane (dppm) gave [(R-C(wedge)N(wedge)C)2Pt2(mu-dppm)] (4a-d). Both head-to-head (syn) and head-to-tail (anti) conformations were found for 4a.6CHCl3.C5H12, whereas only one conformation was observed for 4b.2CHCl3 (syn), 4c.3CH2Cl2 (syn), and 4d.2CHCl3 (anti). In the crystal structures of 4a-d, there are close intramolecular Pt...Pt contacts of 3.272-3.441 A in the syn conformers, and long intramolecular Pt...Pt separations of 5.681-5.714 A in the anti conformers. There are weak C-H...X (d = 2.497-3.134 A) and X...X (X = Cl or Br; d = 2.973-3.655 A) interactions between molecules 4a-d and occluded CHCl3/CH2Cl2 molecules, and their solvent channels are of varying diameters (approximately 9-28 A). Complexes 2a-d, 3, and 4a-d are photoluminescent in the solid state, with emission maxima at 602-643 nm. Upon exposure to volatile organic compounds, 4a shows a fast and reversible vapoluminescent response, which is most intense with volatile halogenated solvents (except CCl4). Powder X-ray diffraction analysis of desolvated 4a revealed a more condensed molecular packing of syn and anti complexes than crystal 4a.6CHCl3.C5H12.

Emissive or Nonemissive? A Theoretical Analysis of the Phosphorescence Efficiencies of Cyclometalated Platinum(II) Complexes

“…deviations 0.06 and 68), [15,16,19,22,26,35] except for 4, for which the PtÀN lat and PtÀ C lat distances were calculated to be 2.170 and 1.998 , respectively (N lat and C lat are respectively the nitrogen atom of the lateral isoquinolinyl ring and the carbon atom of the lateral naphthyl ring directly coordinated to the Pt II ion). The corresponding X-ray data of 4 were reported to be 1.997 (8) and 2.088(5) , respectively.…”

“…Recently, Yersin and coworkers proposed that closer proximity of the occupied d orbitals in quasi-octahedral transition metal complexes than in quasi-square-planar transition metal complexes is likely the reason why the former are usually better emitters than the latter. [20,21] In this work, we attempt to provide a theoretical basis to account for the luminescence properties of a family of square-planar platinum(II) complexes 1-5 with tridentate cyclometalated ligands, which have received widespread interest in recent years because 1) they are strongly emissive when the platinum(II) ion is coordinated to appropriate auxiliary ligands; [15,16,22] 2) their emission intensities are sensitive to their local environments; [17,[23][24][25] 3) their open square-planar geometries allow intermolecular interactions, which in turn significantly change the emission intensities and energies; [19,26] and 4) they have demonstrated usefulness in optoelectronic device applications such as high performance white-light and near-infrared organic lightemitting diodes, as well as luminescent probes for signaling studies. [19,[27][28][29][30][31] …”

Luminescent PtII Complexes of Tridentate Cyclometalating 2,5‐Bis(aryl)‐pyridine Ligands

“…Consequently, the idea arose of using tridentate dicarbanionic cyclometalating ligands of the 2,6-di(phen-2-yl)pyridine ( -PhPyPh -, see Scheme 1) type with Pt II . [21][22][23][24][25][26][27][28][29][30][31][32] Recently, Che et al employed several derivatives of this ligand type, with the aim of providing suitable excited states through variation of the 2,5-aryl groups at the central pyridine unit, and they achieved very efficient triplet emitters, which show phosphorescence, even at room temperature. One crucial move in their ligand design was the use of thiophene as one of their pending metalated aryl groups, with complex 4 in Scheme 2 being the most efficient triplet emitter.…”

Chromo- and Fluorogenic Organometallic Sensors

“…In other examples, Pt-Pt interactions are not directly involved in the vapochromic behaviour of the complexes [90,91]. For example, crystals of the intensely luminescent solvated complex 10a 6CHCl 3 Á C 5 H 12 ( Fig.…”

“…For example, crystals of the intensely luminescent solvated complex 10a 6CHCl 3 Á C 5 H 12 ( Fig. 10) change colour on desolvation and show a significant decrease in emission intensity [91]. The original colour and intense emission are restored upon exposition to the vapour of halogenated solvents or small polar VOCs (e.g.…”