As part of our efforts to discover simple routes to room-temperature phosphors, we have investigated the interaction of bis(pentafluorophenyl)mercury (1) or trimeric perfluoro-o-phenylene mercury (2) with selected arenes (naphthalene, biphenyl, and fluorene). Solution studies indicate that 2, unlike 1, quenches the fluorescence of naphthalene. When compared to 1, the high quenching efficiency of 2 may be correlated to the higher affinity that 2 displays for arenes as well as to more acute external heavy-atom effects caused by the three mercury atoms. In the crystal, the adducts [1.naphthalene], [1.biphenyl], [1.fluorene], and [2.fluorene] form supramolecular binary stacks in which the arene approaches the mercury centers of 1 or 2 to form Hg-C pi-interactions. Analysis of the electrostatic potential surfaces of the individual components supports the involvement of electrostatic interactions. The luminescence spectra of the adducts show complete quenching of the fluorescence and display heavy-atom-induced emission whose energies and vibronic progressions correspond to the phosphorescence of the respective pure arene. The phosphorescence lifetimes are shortened by 3 or 4 orders of magnitude when compared with those of the free arenes. Taken collectively, the structural, photophysical, and computational results herein suggest that the proximity of the three mercury centers serves to enhance the Lewis acidity of 2, which becomes a better acceptor and a more effective heavy-atom effect inducer than 1.
The 1-halonaphthalenes series has often been used to demonstrate the internal heavy-atom effect provided by
the halide. In a continuation of our work on the phosphorescence of arenes induced by π-complexation to
trimeric perfluoro-ortho-phenylene mercury (1), we now present a structural and photophysical study of the
halonaphthalene adducts [1·1-chloronaphthalene] (2), [1·1-bromonaphthalene] (3), and [1·1-iodonaphthalene]
(4). The triplet lifetimes in these adducts are considerably shorter than those for the free 1-halonaphthalenes.
Analysis of lifetime data versus temperature affords room-temperature phosphorescence quantum yields of
70%, 64%, and 7% for the solid adducts 2, 3, and 4, respectively, compared to 54% for [1·naphthalene]. The
photophysical data suggest that the synergy of the internal and external heavy-atom effects has a sensitizing
effect for adducts 2 and 3 but a quenching effect for adduct 4 compared to [1·naphthalene]. The luminescence
excitation spectra of the solid binary adducts show intense bands that are significantly red-shifted from the
absorptions of the individual molecular components, and thus assigned to charge transfer (CT) states. Excitation
bands corresponding to the S0 → T1 direct absorption of the 1-halonaphthalene are also detected, albeit much
less intense than the CT absorption. The spectral analyses suggest that CT is the major excitation route that
leads to the green phosphorescence of adducts 2−4.
The complexation of N-methylcarbazole and N-methylindole by trimeric perfluoro-o-phenylene mercury (1), which can be readily observed in CH2Cl2 solution, leads to the formation of [1.N-methylindole] (2) and [1.N-methylcarbazole] (3) as solid adducts. The solid-state photoluminescence spectra of these adducts show intense emission bands attributed to monomer phosphorescence of N-methylindole and N-methylcarbazole, respectively, with microsecond lifetimes. Remarkably, the triplet lifetimes of the heterocycles in 2 and 3 are shortened by 5 orders of magnitude when compared to those of the free heterocycles. These results are rationalized by invoking the combined external and internal spin-orbit coupling perturbation provided by the mercury and nitrogen atoms.
Both pentafluorophenylmercury chloride and trimeric perfluoro-ortho-phenylene mercury interact with phenanthrene to form phosphorescent adducts which exhibit extended binary stacks in the solid state.
North Sea wells drilled in high-pressure, high-temperature (HPHT) areas are known for presenting barite sag challenges. Fluid densities in the 17.5-18.0 lbm/gal range require a high percentage of barite, and 400°F temperatures can adversely impact the rheological properties needed for reliable suspension. Further, horizontal and extended reach drilling (ERD) wells can require specific hydraulic parameters for hole cleaning that may entail comparatively high pump rates which can contribute to excessive equivalent circulating densities (ECD).Drilling fluid companies initially responded to these challenges by utilizing modified barite and alternative weighting agents. Micronized barite has been used to help lower ECD values for years. However, a non-barite manganese tetraoxide weighting agent has proven to provide equivalent anti-sag at a lower cost. The sub-micron sized material has a specific gravity (sg) of 4.8, which is higher than barite. Per Stokes' law, small particles settle more slowly so that sag resistance improves which is important during extended static periods like during extensive coring operations. Manganese tetraoxide is also acid-soluble. These parameters provide more operational flexibility.The manganese tetraoxide weight material has now been tested successfully in a clay-free and economical paraffin/mineral oil-based fluid (OBF) for use in North Sea HPHT applications. The low-solids, clay-free system has a long history of reducing ECD and minimizing downhole losses while drilling, running casing and cementing. The 17.9 lbm/gal fluid weighted with manganese tetraoxide material exhibits effective hole cleaning properties at lower viscosities than conventional OBFs and shows no detectable sag tendency. Clay-free fluids also demonstrate excellent return permeability values in a wide range of well types. This paper details the design and testing of the clay-free ERD system, including extreme HPHT static aging and sag testing and modifications to the emulsifier package. The economics of implementing the commercial system are also discussed.
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