Light-Emitting Tridentate Cyclometalated Platinum(II) Complexes Containing σ-Alkynyl Auxiliaries:  Tuning of Photo- and Electrophosphorescence

Abstract

The synthesis and structural, photophysical, electrochemical, and electroluminescent properties of a class of platinum(II) complexes bearing sigma-alkynyl ancillary ligands, namely [(C/N/N)Pt(C[triple bond]C]nR] [H(C/N/N) = 6-aryl-2,2'-bipyridine; n = 1-4; R = aryl, alkyl, or trimethylsilyl], have been studied. Substituents with different steric and electronic properties were introduced into the tridentate cyclometalating and arylacetylide ligands, and the pi-conjugation length of the oligoynyl moiety was homologously extended from ethynyl to octatetraynyl. The X-ray crystal structures of several derivatives confirm the Pt-(CC) ligation and reveal various intermolecular interactions, such as pi-pi, Pt...Pt, and C-H...F-C. The complexes display good thermal stability and intense phosphorescence in fluid and glassy solutions with high quantum yields and microsecond lifetimes. Their emission energies are sensitive to solvent polarity, the electronic affinities of the substituents on both the cyclometalating and arylacetylide groups, and the length of the oligoynyl ligand. By choosing appropriate cyclometalating and sigma-alkynyl ligands, the emission color of this class of platinum(II) complexes can be tuned from green-yellow to saturated red. In addition to (3)MLCT [Pt(5d) --> pi*(C/N/N)] and (3)IL(C/N/N), intriguing (3)IL(alkynyl) excited states localized on -(C[triple bond]C)(4)- and -(C[triple bond]Cpyrenyl-1) moieties that afford narrow-bandwidth emissions have been observed. Selected Pt(II) complexes were doped into the emissive region of multilayer, vapor-deposited organic light-emitting diodes. The tunable electrophosphorescence energy resembles that recorded in fluid solutions for these emitters, and the devices exhibit high luminance and efficiencies (up to 4.2 cd A(-1)).

Novel N^C^N-cyclometallated platinum complexes with acetylide co-ligands as efficient phosphors for OLEDs

“…17,21 Various attempts to substitute the chloride in these complexes by the ethynyl-3,5-difluorobenzene anion following Sonogashira's synthetic route, which has been shown to be suitable for preparing acetylide derivatives of cyclometallated N^N^C and O^N^N Pt(II) complexes, 14,26,27 were unsuccessful, despite the screening of different catalytic systems (for example, CuI-iPr 2 The new Pt(II) acetylide complexes were fully characterized by elemental analyses and by IR and NMR spectroscopies.…”

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

“…[1,2,[4][5][6][7][8][9][10][11][12][13][14] Very soon after their initial use, it was found that many Pt II derivatives of the Phbpy ligand show intense luminescence, some even at ambient temperature. [11,[15][16][17][18][19] One reason lies in the destabilisation of dark metal-centred excited states associ-to 0.44 in PMMA matrices. Detailed electrochemistry (including spectroelectrochemistry) reveals reversible ligand-based first reductions at -2.1 to -2.3 V, irreversible Pt-centred oxidations at around 0.8 V and electrochemical band gaps of 2.8-3.0 eV.…”

Recent advances in white organic light-emitting diodes employing a single-emissive material

“…65 Furthermore, the formation of molecular aggregates tends to quench the emission and excimer emission is rarely observed in these classes of complexes. 66 Pt complexes employing N^C^N cyclometalating ligands, on the other hand, have shown very high Ф across a wide range of emission energies and can exhibit strong excimer emission. The success of this class can be attributed to the strong ligand field induced by the cyclometalating carbon-Pt bond, leading to an increase of the d-d state energy.…”