Marie-Hélène Thibault

Fluorescence in rhoda- and iridacyclopentadienes neglecting the spin-orbit coupling of the heavy atom: the ligand dominates.

We present a detailed photophysical study and theoretical analysis of 2,5-bis(arylethynyl)rhodacyclopenta-2,4-dienes (1a–c and 2a–c) and a 2,5-bis(arylethynyl)iridacyclopenta-2,4-diene (3). Despite the presence of heavy atoms, these systems display unusually intense fluorescence from the S1 excited state and no phosphorescence from T1. The S1 → T1 intersystem crossing (ISC) is remarkably slow with a rate constant of 108 s–1 (i.e., on the nanosecond time scale). Traditionally, for organometallic systems bearing 4d or 5d metals, ISC is 2–3 orders of magnitude faster. Emission lifetime measurements suggest that the title compounds undergo S1 → T1 interconversion mainly via a thermally activated ISC channel above 233 K. The associated experimental activation energy is found to be ΔHISC = 28 kJ mol–1 (2340 cm–1) for 1a, which is supported by density functional theory (DFT) and time-dependent DFT calculations [ΔHISC(calc.) = 11 kJ mol–1 (920 cm–1) for 1a-H]. However, below 233 K a second, temperature-independent ISC process via spin–orbit coupling occurs. The calculated lifetime for this S1 → T1 ISC process is 1.1 s, indicating that although this is the main path for triplet state formation upon photoexcitation in common organometallic luminophores, it plays a minor role in our Rh compounds. Thus, the organic π-chromophore ligand seems to neglect the presence of the heavy rhodium or iridium atom, winning control over the excited-state photophysical behavior. This is attributed to a large energy separation of the ligand-centered highest occupied molecular orbital (HOMO) and lowest unoccupied MO (LUMO) from the metal-centered orbitals. The lowest excited states S1 and T1 arise exclusively from a HOMO-to-LUMO transition. The weak metal participation and the cumulenic distortion of the T1 state associated with a large S1–T1 energy separation favor an “organic-like” photophysical behavior.

Synthesis and solid-state characterization of platinum complexes with hexadentate amino- and iminophosphine ligands

Hexadentate ligands cis,cis-C(6)H(9)(N[double bond, length as m-dash]CHC(6)H(4)(PPh(2)))(3) () and cis,cis-C(6)H(9)(NHCH(2)C(6)H(4)(PPh(2)))(3) () were synthesized starting from cis,cis-1,3,5-triaminocyclohexane, and characterized using NMR spectroscopy and single-crystal X-ray diffraction. These ligands can bind both Pt(0) and Pt(II) metal centers using either or both of the soft phosphine moieties and the hard amine/imine moieties. In many cases the resulting complexes are negligibly soluble; hence, (31)P and (195)Pt solid-state NMR (SSNMR) spectroscopy was applied to analyse the bonding modes of the hexadentate ligands. The (195)Pt SSNMR spectroscopy of these complexes is particularly challenging, since (1)H-(195)Pt cross polarization is extremely inefficient, the (195)Pt longitudinal relaxation times are extremely long and the (195)Pt powder patterns are expected to be quite broad due to platinum chemical shift anisotropy. It is demonstrated that the ultra-wideline (195)Pt SSNMR spectra can be efficiently acquired with a combination of frequency-stepped piecewise acquisitions and cross-polarization/Carr-Purcell Meiboom-Gill (CP/CPMG) NMR experiments. The (195)Pt and (31)P SSNMR data are correlated to important structural features in both Pt(0) and Pt(II) species.

Characterization of Shrimp Oil from Pandalus borealis by High Performance Liquid Chromatography and High Resolution Mass Spectrometry

Northern shrimp (Pandalus borealis) oil, which is rich in omega-3 fatty acids, was recovered from the cooking water of shrimp processing facilities. The oil contains significant amounts of omega-3 fatty acids in triglyceride form, along with substantial long-chain monounsaturated fatty acids (MUFAs). It also features natural isomeric forms of astaxanthin, a nutritional carotenoid, which gives the oil a brilliant red color. As part of our efforts in developing value added products from waste streams of the seafood processing industry, we present in this paper a comprehensive characterization of the triacylglycerols (TAGs) and astaxanthin esters that predominate in the shrimp oil by using HPLC-HRMS and MS/MS, as well as 13C-NMR. This approach, in combination with FAME analysis, offers direct characterization of fatty acid molecules in their intact forms, including the distribution of regioisomers in TAGs. The information is important for the standardization and quality control, as well as for differentiation of composition features of shrimp oil, which could be sold as an ingredient in health supplements and functional foods.

(η4-Cyclo­octa-1,5-diene)diiodidoplatinum(II)

The monoclinic title complex, [PtI2(C8H12)], characterized by a twisted cyclooctadiene ring, is similar to its Cl and Br orthorhombic homologues. The observed Pt—I bond distances of 2.6094 (5) and 2.6130 (5) Å are in the expected range for PtI2 complexes. The C=C double bonds in the molecule differ significantly [1.373 (10) and 1.403 (10) Å]. As expected for a platinum(II) complex, the PtII atom is in a square-planar environment (ΣPtα= 359.71°).

rac‐2,2′‐Bis(diphenylphosphinoyl)‐1,1′‐binaphthyl

In the structure of the title compound, C44H32O2P2, the dihedral angle between the naphthyl ring systems is 88.74 (4)°.