π−π Interactions in Organometallic Systems. Crystal Structures and Spectroscopic Properties of Luminescent Mono-, Bi-, and Trinuclear Trans-cyclometalated Platinum(II) Complexes Derived from 2,6-Diphenylpyridine

Abstract

A series of mono-and multinuclear dicyclometalated platinum(II) complexes, namely, [Pt-(C ∧ N ∧ C)L 1 ] [HC ∧ N ∧ CH ) 2,6-diphenylpyridine; L 1 ) 4-tert-butylpyridine (1), 1-methyl-4,4′bipyridinium (MQ + ) hexafluorophosphate (2(PF 6 )), 2,6-dimethylphenylisocyanide (4), tricyclohexylphosphine (5), triphenylphosphine ( 7) pyrazine (pyr; 3), bis(dicyclohexylphosphino)methane (dcpm; 6), bis(diphenylphosphino)methane (dppm; 8)], and [Pt 3 (C ∧ N ∧ C) 3 (µ 3 -dpmp)] [dpmp ) bis(diphenylphosphinomethyl)phenylphosphine (9)], were synthesized from [Pt(C ∧ N ∧ C)dmso] (dmso ) dimethyl sulfoxide). The X-ray crystal structures of 1, 3‚CHCl 3 , 4, 6‚CHCl 3 ‚CH 3 OH‚4H 2 O, 7, 8 (yellow form), and 8‚CHCl 3 (orange form) have been determined. For complex 1, the Pt(C ∧ N ∧ C) units are oriented into pairs in a head-to-tail fashion with an interplanar separation of 3.40 Å. For complex 4, dimeric π-π overlap between Pt(C ∧ N ∧ C) and phenyl moieties in a head-to-tail manner is observed, with interplanar stacking at 3.39 Å. There are two crystal forms for complex 8. Only one intramolecular Pt(C ∧ N ∧ C)-phenyl π-π interaction (separation 3.381 Å) is apparent in the yellow form. For the orange form (8‚CHCl 3 ), there are two intramolecular Pt(C ∧ N ∧ C)-phenyl π-π contacts (separations 3.115 and 3.287 Å). For 3‚CHCl 3 , the dihedral angles between the pyrazine and the two Pt(C ∧ N ∧ C) planes are 124.0°and 130.5°, which allows the possibility for partial orbital interaction between the (5d)Pt and pπ*(pyrazine) orbitals. Complexes 1 and 4-9 display vibronically structured emission (λ max of most intense band ) 508-526 nm) in 77 K methanol/ethanol (1:5, v/v) glass, which are assigned to 3 IL excited states. For 1, 4-6, 8, and 9, the 77 K structureless emission at λ max 596-636 nm in methanol/ethanol glasses is assigned as ππ* excimeric in nature. These excimeric emissions are concentrationdependent for 1 and 4-6 and concentration-independent for 8 and 9. The 298 K solid emission spectra of 1, 4-6, 8, and 9 are characterized by a broad, unstructured band at λ max 566-633 nm, which red-shift in energy upon cooling to 77 K. These bands are comparable in energy to the 77 K glassy emissions and are similarly assigned. Complexes 2 and 3 show an intense absorption at λ max 410 (shoulder) and 456 nm, which are ascribed to the MLCT (5d)Pt f π*(1-methyl-4,4′-bipyridinium/pyrazine) transition, respectively. Likewise, the solid-state emissions of 2 and 3 at λ max 686 and 658 nm, respectively, are assigned as MLCT. The vapochromism of complex 8 has been investigated.

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.…”

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

“…However, complexes [PtA C H T U N G T R E N N U N G (CNC)X] (X = an auxiliary ligand) are usually nonemissive in solution at room temperature, regardless of whether X is a strong s-alkynyl donor [18] or a strong p acceptor. [19] Therefore, a thorough understanding of the effect of the coordinating ligands on the photophysical behavior of a transition metal complex is desirable for rational syntheses of highly phosphorescent materials. 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.…”

“…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] …”

Dynamic Vapochromic Behaviors of Organic Crystals Based on the Open–Close Motions of S‐Shaped Donor–Acceptor Folding Units

“…Development of vapochromic materials and their mechanistic studies are subjects of importance in view of basic science of stimuli-responsive color change, [1][2][3][4][5][6][7][8] and future applications in sensing volatile organic compounds. [9] Two major strategies have been adopted to bestow vapochromic properties on materials.…”

“…Remarkable changes in color and emission have been observed using a variety of transition-metal assemblies for which adsorption and desorption of organic vapors lead to significant variations in M-M interactions, [4,5] coordination modes, [6] conformation of p-conjugated ligands [7] and stacking interactions between coordination planes. [8] Crystal design is a forward-looking strategy for the development of functional vapochromic materials, as adsorption properties and color change can be Abstract: The first vapochromic organic crystals are described with respect to their preparation, color change, adsorption/desorption properties, crystal structures, and color-change mechanism. Non-solvatochromic, 1,4,5,8-naphthalene-tetracarboxylic diimide (NDI) derivatives 1 a bearing two pyrrole imine (PI) tethers have been used as a motif for the crystal packing template.…”