Pt(ii) mono-carbonyl complexes of a cyclometallating 2-(2′-thienyl)-(pyridinato-C,3N′) ligand: nature and dynamics of the lowest excited state of the chloro- and thiolato-complexes

Synthesis and Structural Studies of Cu(I) Methylthiosalicylate Complexes and their Catalytic Application in Thiol-Yne Click Reaction

Three complexes of Cu(I), [Cu(PPh3)2(mts)] (1), [Cu(dppf)(mts)] (2), [Cu(dppe)(mts)]2 (3) (mts = methylthiosalicylate; dppf = dipheylphosphinoferrocene; dppe = diphenylphosphinoethane) have been synthesized and characterized. Complexes 1 and 2 have monomeric...

Structure and ultrafast dynamics of the charge-transfer excited state and redox activity of the ground state of mono- and binuclear platinum(II) diimine catecholate and bis-catecholate complexes: a transient absorption, TRIR, DFT, and electrochemical study

A series of mononuclear complexes of the type [Pt(Bu(2)cat)(4,4'-R(2)-bipy)] [where Bu(2)cat is the dianion of 3,5-(t)Bu(2)-catechol and R = H, (t)Bu, or C(O)NEt(2)] and analogous dinuclear complexes based on the "back-to-back" bis-catechol ligand 3,3',4,4'-tetrahydroxybiphenyl have been studied in detail in both their ground and excited states by a range of physical methods including electrochemistry, UV/vis/near-IR, IR, and electron paramagnetic resonance spectroelectrochemistry, and time-resolved IR (TRIR) and transient absorption (TA) spectroscopy. Density functional theory calculations have been performed to support these studies, which provide a detailed picture of the ground- and excited-state electronic structures, and excited-state dynamics, of these complexes. Notable observations include the following: (i) for the first time, the lowest-energy catecholate → bipyridine (bpy) ligand-to-ligand charge-transfer (LL'CT) excited states of these chromophores have been studied by TRIR spectroscopy, showing a range of transient bands associated with the bpy radical anion and semiquinone species, and back-electron-transfer occurring in hundreds of picoseconds; (ii) strong electronic coupling between the two catecholate units in the bridging ligand of the dinuclear complexes results in a delocalized, planar (class 3) "mixed-valence" catecholate(2-)/semiquinone(•-) state formed by one-electron oxidation of the bridging ligand; (iii) in the LL'CT excited state of the dinuclear complexes, the bridging ligand is symmetrical and delocalized, whereas the bpy radical anion is localized at one terminus of the complex. This study is the first example of an investigation of excited-state behavior in platinum(II) catecholate complexes, performed with the use of picosecond TRIR and femtosecond TA spectroscopy.

Photophysical properties of platinum(II)-acetylide complexes: the effect of a strongly electron-accepting diimine ligand on excited-state structure

The compounds [Pt(MesBIAN)(C[triple bond]CR)2] (R = C6H4-CN-p, 1; SiMe3, 2; C6H4-CF3-p, 3; C6H5, 4; C6H4-CH3-p 5) {MesBIAN = bis(mesitylimino)acenaphthene} have been synthesized; the X-ray crystal structure determinations of 4 and 5 and the starting material [Pt(MesBIAN)Cl2] are reported. Chemical oxidation of 4 with diiodine leads to generation of an intermediate platinum(IV) bis(acetylide) diiodide complex, which then couples and reductively eliminates the acetylide ligands as a diyne, leading to the generation of [Pt(MesBIAN)I2] 6. Compound 2 readily forms an adduct 2a with copper(I) chloride, in which the copper atom is bonded to the two acetylide triple bonds. 1-5 each undergo an irreversible oxidation, and a reversible one-electron reduction to generate a stable anion. ESR studies of 1(-)-5(-) show that the unpaired electron is localized mainly on the pi* orbital of the coordinated MesBIAN ligand, with about 10% platinum contribution to the singly occupied molecular orbital (SOMO). The compounds show a strong absorption at around 500 nm in the UV/visible spectrum, which is assigned to a "mixed metal-ligand to ligand charge transfer" (MMLL'CT) transition; this assignment is supported by time-dependent density-functional theory (TD-DFT) calculations on 5. 1-5 emit in the near-infrared region from a (3)MMLL'CT excited state, with lifetimes ranging from 8 to 36 ns. Picosecond and nanosecond time-resolved infrared (TRIR) spectroscopy has been used to probe directly the nature and dynamics of the excited state of 5. The TRIR data show a decrease of the energy of the C[triple bond]C vibration upon excitation, by about 90 cm(-1) in comparison to the ground state, and formation of a new, very intense, and very broad band at 1820 cm(-1). We propose that the excited-state structure contains some contribution from a pseudo-cumulenic form of the platinum-acetylide moiety, which is supported by TD-DFT calculations. Picosecond TRIR allowed determination of the rate of vibrational relaxation (14 ps) of the vibrationally "hot" electronic excited state of 5 formed upon initial laser excitation.

Deep-red luminescence and efficient singlet oxygen generation by cyclometalated platinum(II) complexes with 8-hydroxyquinolines and quinoline-8-thiol

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%.

Probing the Excited States of d6 Metal Complexes Containing the 2,2‘-Bipyrimidine Ligand Using Time-Resolved Infrared Spectroscopy. 1. Mononuclear and Homodinuclear Systems

This paper reports time-resolved infrared (TRIR) spectroscopic studies on a series of weakly luminescent or nonluminescent 2,2'-bipyrimidine-based complexes to probe their electronic structure and the dynamic behavior of their excited states on the picosecond and nanosecond time scales. The complexes are mononuclear [Re(CO)3Cl(bpm)] (1), [Ru(CN)4(bpm)]2- (2), and [Ru(bpyam)2(bpm)]2+ (3) [bpm=2,2'-bipyrimidine; bpyam=2,2'-bipyridine-4,4'-(CONEt2)2] and their homodinuclear analogues [{Re(CO)3Cl}2(mu-bpm)] (4), [{Ru(CN)4}2(mu-bpm)]2- (5), and [{Ru(bpyam)2}2(mu-bpm)]4+ (6). Complex 1 shows the characteristic shift of the three nu(CO) bands to higher energy in the Re-->bpm triplet metal-to-ligand charge-transfer (3MLCT) state, which has a lifetime of 1.2 ns. In contrast, the dinuclear complex 4 shows nu(CO) transient bands to both higher and lower energy than the ground state indicative of, on the IR time scale, an asymmetric excited state [(OC)3ClReI(bpm*-)ReII(CO)3Cl] whose lifetime is 46 ps. The cyanoruthenate complexes 2 and 5 show comparable behavior, with a shift of the nu(CN) bands to higher energy in the excited state for mononuclear 2 but two sets of transient bands-one to higher energy and one to lower energy-in dinuclear 5, consistent with an asymmetric charge distribution [(NC)4RuII(bpm*-)RuIII(CN)4]4- in the 3MLCT state. These cyanoruthenate complexes have much longer lifetimes in D2O compared with CH3CN, viz., 250 ps and 3.4 ns for 2 and 65 ps and 1.2 ns for 5 in CH3CN and D2O, respectively. In complex 3, both higher-energy Ru-->bpyam and lower-energy Ru-->bpm 3MLCT states are formed following 400 nm excitation; the former decays rapidly (tau=6-7 ps) to the latter, and the subsequent decay of the Ru-->bpm 3MLCT state occurs with a lifetime of 60 or 97 ns in D2O or CH3CN, respectively. Similar behavior is shown by dinuclear 6 in both D2O and CH3CN, with initial interconversion from the Ru-->bpyam to the Ru-->bpm 3MLCT state occurring with tau approximately 7 ps and the resultant Ru-->bpm 3MLCT state decaying on the nanosecond time scale.