We report new bis-cyclometalated cationic iridium(III) complexes [(C(^)N)(2)Ir(CN-tert-Bu)(2)](CF(3)SO(3)) that have tert-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4'-fluorophenyl)-R-pyridines (where R is 4-methoxy, 4-tert-butyl, or5-trifluoromethyl) as C(^)N ligands. The complexes are white or pale yellow solids that show irreversible reduction and oxidation processes and have a large electrochemical gap of 3.58-3.83 V. They emit blue or blue-green phosphorescence in liquid/solid solutions from a cyclometalating-ligand-centered excited state. Their emission spectra show vibronic structure with the highest-energy luminescence peak at 440-459 nm. The corresponding quantum yields and observed excited-state lifetimes are up to 76% and 46 μs, respectively, and the calculated radiative lifetimes are in the range of 46-82 μs. In solution, the photophysical properties of the complexes are solvent-independent, and their emission color is tuned by variation of the substituents in the cyclometalating ligand. For most of the complexes, an emission color red shift occurs in going from solution to neat solids. However, the shift is minimal for the complexes with bulky tert-butyl or trifluoromethyl groups on the cyclometalating ligands that prevent aggregation. We report the first example of an iridium(III) isocyanide complex that emits blue phosphorescence not only in solution but also as a neat solid.

Mononuclear complexes [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] (bpym = 2,2'-bipyrimidine), in which one of the bipyrimidine sites is vacant, have been used as "complex ligands" to prepare heterodinuclear d-f complexes in which a lanthanide tris(1,3-diketonate) unit is attached to the secondary bipyrimidine site to evaluate the ability of d-block chromophores to act as antennae for causing sensitized near-infrared (NIR) luminescence from adjacent lanthanide(III) centers. The two sets of complexes so prepared are [Re(CO)(3)Cl(mu-bpym)Ln(fod)(3)] (abbreviated as Re-Ln; where Ln = Yb, Nd, Er) and [(F(3)C-C(6)H(4)-CC)(2)Pt(mu-bpym)Ln(hfac)(3)] (abbreviated as Pt-Ln; where Ln = Nd, Gd). Members of both series have been structurally characterized; the metal-metal separation across the bipyrimidine bridge is approximately 6.3 A in each case. In these complexes, the (3)MLCT (MLCT = metal to ligand charge-transfer) luminescences of the mononuclear [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] complexes are quenched by energy transfer to those lanthanides (Ln = Yb, Nd, Er) that have low-lying f-f states capable of NIR luminescence; as a result, sensitized NIR luminescence is seen from the lanthanide center following excitation of the d-block unit. In the solid state, quenching of the luminescence from the d-block chromophore is complete, indicating efficient d --> f energy transfer, as a result of the short metal-metal separation across the bipyrimidine bridge. In a CH(2)Cl(2) solution, partial dissociation of the dinuclear complexes into the mononuclear units occurs, with the result that some (3)MLCT luminescence is observed from mononuclear [Re(bpym)(CO)(3)Cl] or [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] present in the equilibrium mixture. Solution UV-vis and luminescence titrations, carried out by the addition of portions of Ln(fod)(3)(H(2)O)(2) or Ln(hfac)(3)(H(2)O)(2) to the d-block complex ligands, indicate that binding of the lanthanide tris(1,3-diketonate) unit at the secondary bipyrimidine site to give the d-f dinuclear complexes occurs with an association constant of ca. 10(5) M(-)(1).

Reaction of the potentially bis-bidentate bridging ligand 3,6-bis(2-pyridyl)tetrazine (BPTZ) with various lanthanide complexes [Ln(tta) 3 (H 2 O) 2 ] [Htta = thenoyl(trifluoro)acetone; Ln = La, Nd, Gd, Er, Yb] in aqueous ethanol afforded the mononuclear complexes [Ln(tta) 3 (BPTZ)] (Ln = La, Nd) or the dinuclear complexes [{Ln(tta) 3 } 2 (µ-BPTZ)] (Ln = Gd, Er, Yb) in which one or two, respectively, lanthanide tris-diketonate {Ln(tta) 3 } units are bound to the N,N-bidentate compartments of BPTZ. Crystal structures of the dinuclear complexes [{Yb(tta) 3 } 2 (µ-BPTZ)]ؒCH 2 Cl 2 and [{Gd(tta) 3 } 2 (µ-BPTZ)]ؒ2CH 2 Cl 2 show that the metal centres have an approximately square-antiprismatic eightcoordinate geometry; there are close contacts above and below the plane of the BPTZ bridging ligand between peripheral trifluoromethyl groups from a tta ligand associated with each metal centre. It is not apparent why the larger lanthanides La and Nd only give a mononuclear complex whereas the smaller lanthanides Gd, Er and Yb give the dinuclear complex in each case. UV/Vis spectroscopic titrations of a solution of BPTZ in CH 2 Cl 2 with increasing amounts of [Ln(tta) 3 (H 2 O) 2 ] (Ln = La and Yb) show very similar behaviour, with stepwise binding constants K 1 and K 2 for association of the two {Ln(tta) 3 } units of ca. 10 6 M Ϫ1 and 10 5 M Ϫ1 ; allowing for the expected statistical factor of 4 there is an additional reduction in the value of K 2 compared to K 1 which may be associated with a steric interaction between the two {Ln(tta) 3 } units when the dinuclear complex forms. Steady-state and time-resolved luminescence studies on the complexes with Yb, Nd and Er, both in the solid state and CH 2 Cl 2 solution, show that near-IR luminescence on the microsecond timescale can be sensitised by irradiation either at 337 nm into the tta-based transition, or at 520 nm into the low-energy BPTZ-centred transition.

The synthesis and photophysical study of (C/\N)Pt(II)Q complexes, where C/\N is a bidentate cyclometalating ligand and Q is 8-hydroxyquinoline or quinoline-8-thiol, are presented. The compounds were obtained as a single isomer with N atoms of the C/\N and Q ligands trans-coordinated to the Pt(II) center as shown by X-ray crystallography. These chromophores absorb intensely in the visible region and emit in the deep-red spectral region from a quinolate-centered triplet intraligand charge-transfer excited state. The emission maxima are in the range 675-740 nm, with the quantum yields and lifetimes of up to 0.82% and 5.3 mus, respectively, in deoxygenated organic solvents at room temperature. These complexes are efficient photosensitizers of singlet oxygen in air-saturated solutions, with yields up to 90%.