Long-lived room temperature deep-red/near-IR emissive intraligand triplet excited state (3IL) of naphthalimide in cyclometalated platinum(II) complexes and its application in upconversion

[C(^)NPt(acac)] (C(^)N = cyclometalating ligand; acac = acetylacetonato) complexes in which the naphthalimide (NI) moiety is directly cyclometalated (NI as the C donor of the C-Pt bond) were synthesized. With 4-pyrazolylnaphthalimide, isomers with five-membered (Pt-2) and six-membered (Pt-3) chelate rings were obtained. With 4-pyridinylnaphthalimide, only the complex with a five-membered chelate ring (Pt-4) was isolated. A model complex with 1-phenylpyrazole as the C(^)N ligand was prepared (Pt-1). Strong absorption of visible light (ε = 21,900 M(-1) cm(-1) at 443 nm for Pt-3) and room temperature (RT) phosphorescence at 630 nm (Pt-2 and Pt-3) or 674 nm (Pt-4) were observed. Long-lived phosphorescences were observed for Pt-2 (τ(P) = 12.8 μs) and Pt-3 (τ(P) = 61.9 μs). Pt-1 is nonphosphorescent at RT in solution because of the acac-localized T(1) excited state [based on density functional theory (DFT) calculations and spin density analysis], but a structured emission band centered at 415 nm was observed at 77 K. Time-resolved transient absorption spectra and spin density analysis indicated a NI-localized intraligand triplet excited state ((3)IL) for complexes Pt-2, Pt-3, and Pt-4. DFT calculations on the transient absorption spectra (T(1) → T(n) transitions, n > 1) also support the (3)IL assignment of the T(1) excited states of Pt-2, Pt-3, and Pt-4. The complexes were used as triplet sensitizers for triplet-triplet-annihilation (TTA) based upconversion, and the results show that Pt-3 is an efficient sensitizer with an upconversion quantum yield of up to 14.1%, despite its low phosphorescence quantum yield of 5.2%. Thus, we propose that the sensitizer molecules at the triplet excited state that are otherwise nonphosphorescent were involved in the TTA upconversion process, indicating that weakly phosphorescent or nonphosphorescent transition-metal complexes can be used as triplet sensitizers for TTA upconversion.     

Coumarin phosphorescence observed with N^N Pt(II) bisacetylide complex and its applications for luminescent oxygen sensing and triplet-triplet-annihilation based upconversion

A dbbpy platinum(II) bis(coumarin acetylide) complex (Pt-1, dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) was prepared. Pt-1 shows intense absorption in the visible region (λ(abs) = 412 nm, ε = 3.23 × 10(4) M(-1) cm(-1)) compared to the model complex dbbpy Pt(II) bis(phenylacetylide) (Pt-2, λ(abs) = 424 nm, ε = 8.8 × 10(3) M(-1) cm(-1)). Room temperature phosphorescence was observed for Pt-1 ((3)IL, τ(P) = 2.52 μs, λ(em) = 624 nm, Φ(P) = 2.6%) and the emissive triplet excited state was assigned as mainly intraligand triplet excited state ((3)IL), proved by 77 K steady state emission, nanosecond time-resolved transient absorption spectroscopy and DFT calculations. Complex Pt-1 was used for phosphorescent oxygen sensing and the sensitivity (Stern-Volmer quenching constant K(SV) = 0.012 Torr(-1)) is 12-fold of the model complex Pt-2 (K(SV) = 0.001 Torr(-1)). Pt-1 was also used as triplet sensitizer for triplet-triplet-annihilation based upconversion, upconversion quantum yield Φ(UC) up to 14.1% was observed, vs. 8.9% for the model complex Pt-2.     

Accessing the long-lived emissive 3IL triplet excited states of coumarin fluorophores by direct cyclometallation and its application for oxygen sensing and upconversion

We studied four cyclometallated Pt(II) complexes, in which the thiazo-coumarin ligands (Pt-2, Pt-3 and Pt-4) or the phenylthiazo ligand (Pt-1) were directly cycloplatinated. Pt-2 shows intense absorption in visible region but other complexes show blue-shifted absorption. Room temperature phosphorescence was observed for all the complexes, and the emission wavelength is dependent on the size of the π-conjugation, not the intramolecular charge transfer (ICT) feature of the C^N ligands. Pt-2 shows longer phosphorescence lifetime (τ = 20.3 μs) than other complexes (below 2.0 μs). Furthermore, Pt-2 shows phosphorescence quantum yield Φ = 0.37, whereas Pt-3 and Pt-4 show much smaller Φ values (0.03 and 0.01, respectively). DFT/TDDFT calculations indicate (3)IL triplet excited states for the complexes. The complexes were used as for luminescence O(2) sensing and triplet-triplet-annihilation (TTA) based upconversion. Stern-Volmer quenching constant K(SV) = 0.026 Torr(-1) was observed for Pt-2, ca. 89-fold of that of Pt-3. TTA upconversion is achieved with Pt-2 (λ(em) = 400 nm with λ(ex) = 473 nm, anti-Stokes shift is 0.47 eV, excitation power density is at 70 mW cm(-2)). The upconversion quantum yield with Pt-2 as triplet sensitizer is up to 15.4%. The TTET efficiency (K(SV) = 1.33 × 10(5) M(-1), k(q) = 6.57 × 10(9) M(-1) s(-1). DPA as quencher) of Pt-2 is 34-fold of the model complex [Ru(dmb)(3)][PF(6)](2). Our results show that the (3)IL state can be readily accessed by direct cyclometallation of organic fluorophores and this approach will be useful for preparation and applications of transition metal complexes that show intense absorption in visible region and the long-lived emissive (3)IL excited states.     

Synthesis and assembly with mesoporous silica MCM-48 of platinum(II) porphyrin complexes bearing carbazyl groups: spectroscopic and oxygen sensing properties

The synthesis and spectroscopic characterization of a series of luminescent platinum meso-tetrakis{3,5-di[(N-carbazyl)n-alkyloxyphenyl]}porphyrin (Pt-8Cn-TPP, n-alkyl = (CH2)n, n = 4, 6, and 8) are presented. The protonated platinum porphyrins ([Pt-8Cn-TPPH8]8+) were assembled with mesoporous silica MCM-48 resulting in the assembly materials [Pt-8Cn-TPPH8]8+/MCM-48. The luminescence of [Pt-8Cn-TPPH8]8+/MCM-48 can be extremely quenched by molecular oxygen with very high sensitivity (I0/I100 > 5000) and rapid response time (0.04 s) suggesting that the [Pt-8Cn-TPPH8]8+/MCM-48 system can be employed to develop high performance oxygen sensors. Among this assembly system, [Pt-8C8-TPPH8]8+/MCM-48 exhibits the highest sensitivity. Even if the concentration of oxygen is 0.1%, the luminescence intensity of [Pt-8C8-TPPH8]8+/MCM-48 can be quenched by 86%.     

Experimental and theoretical investigation of the stability of Pt-3d-Pt(111) bimetallic surfaces under oxygen environment

The stability of the Pt-3d-Pt(111) (3d = Ti, V, Cr, Mn, Fe, Co, or Ni) bimetallic surface structures in the presence of adsorbed oxygen has been investigated by means of density functional theory (DFT). The dissociative binding energies of oxygen on Pt-3d-Pt(111) (i.e., subsurface 3d monolayer) and 3d-Pt-Pt(111) (i.e., surface 3d monolayer) were calculated. All of the Pt-3d-Pt(111) surfaces were found to have weaker oxygen binding energies than pure Pt(111) whereas all of the 3d-Pt-Pt(111) surfaces were found to have stronger oxygen binding energies than pure Pt(111). The total heat of reaction was calculated for the segregation for 3d metal atoms from Pt-3d-Pt(111) to 3d-Pt-Pt(111) when exposed to a half monolayer of oxygen. All of the Pt-3d-Pt(111) subsurface structures were predicted to be thermodynamically unstable with adsorbed oxygen. In addition, the segregation of subsurface Ni and Co to the surfaces of Pt-Ni-Pt(111) and Pt-Co-Pt(111) was investigated experimentally using Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS). AES and HREELS confirmed the trend predicted by DFT modeling and showed that both the Pt-Ni-Pt(111) and Pt-Co-Pt(111) surface structures were unstable in the presence of adsorbed oxygen. The activation barrier of the segregation of surbsurface Ni and Co atoms was determined to be 15 +/- 2 and 7 +/- 1 kcal/mol, respectively. These results are further discussed for their implication in the design and selection of cathode bimetallic electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrode membrane (PEM) fuel cells.     

Thermodynamics and kinetics of oxygen-induced segregation of 3d metals in Pt-3d-Pt(111) and Pt-3d-Pt(100) bimetallic structures

The stability of subsurface 3d transition metals (3d represents Ni, Co, Fe, Mn, Cr, V, and Ti) in Pt(111) and Pt(100) was examined in vacuum and with 0.5 ML atomic oxygen by a combined experimental and density functional theory (DFT) approach. DFT was used to predict the trends in the binding energy of oxygen and in the stability of 3d metals to remain in the subsurface layer. DFT calculations predicted that for both (111) and (100) crystal planes the subsurface Pt-3d-Pt configurations were thermodynamically preferred in vacuum and that the surface 3d-Pt-Pt configurations were preferred with the adsorption of 0.5 ML atomic oxygen. Experimentally, the DFT predictions were verified by using Auger electron spectroscopy to monitor the segregation of Ni and Co in Pt-3d-Pt structures on polycrystalline Pt foil, composed of mainly (111) and (100) facets. The activation barrier for the oxygen-induced segregation of Ni was found to be 17+/-1 kcal/mol attributed to the Pt(111) areas and 27+/-1 kcal/mol attributed to the Pt(100) areas of the Pt foil. For Pt-Co-Pt, the activation barrier was found to be 10+/-1 kcal/mol and was attributed to the Pt(111) areas of the Pt foil. The Bronsted-Evans-Polanyi relationship was utilized to predict the activation barriers for segregation of the other Pt-3d-Pt(111) and Pt-3d-Pt(100) systems. These results are further discussed in connection to the activity and stability for cathode bimetallic electrocatalysts for proton exchange membrane fuel cells.     

Intense Red-Blue Luminescence Based on Superfine Control of Metal–Metal Interactions for Self-Assembled Platinum(II) Complexes

A series of assembled Pt^II complexes comprising N-heterocyclic carbene and cyanide ligands was constructed using different substituent groups, [Pt(CN)₂(R-impy)] (R-impyH⁺=1-alkyl-3-(2-pyridyl)-1H-imidazolium, R=Me ( Pt-Me ), Et ( Pt-Et ), ⁱPr ( Pt- ⁱ Pr ), and ^tBu ( Pt- ^t Bu )). All the complexes exhibited highly efficient photoluminescence with an emission quantum yield of 0.51–0.81 in the solid state at room temperature, originating from the triplet metal-metal-to-ligand charge transfer (³MMLCT) state. Their emission colors cover the entire visible region from red for Pt-Me to blue for Pt- ^t Bu . Importantly, Pt- ^t Bu is the first example that exhibits blue ³MMLCT emission. The ³MMLCT emission was proved and characterized based on the temperature dependences of the crystal structures and emission properties. The wide-range color tuning of luminescence using the ³MMLCT emission presents a new strategy of superfine control of the emission color.     

Molecular Mechanics Study on Asymmetry Catalysis

Theasymmetrycatalysisisanimportantchemicalreactionwidelyusedinbiology,pharmacyalldagriculture.Itispreferredtoenantioselectivehydrogenationofmethylpyruvate(MP)oversuppoFtedplatiniumnanoclusters.Cinchonidine(CD)isamodifier,aco-catalysttothereaction.Withoutthemodifier,therewouldbenoenantioselectivitytothehydrogenationofpyruvate.Inordertoobtainbetterunderstandingofthemechanismofthereaction,especiallytheroleofthemoditler,thepresentstudybymolecularmodelinghasbeenperformedandtheresultsarereportedhe…     

ESCA, SIMS, SEM and XRD investigations of Pt-10%Rh catalyst-gauzes

Summary The nature and origin of harmful surface contaminants of spent Pt-10%Rh catalyst gauzes was determined by HR-SEM, ESCA, SIMS and XRD. Based on the analytical results the degree of surface contamination could be greatly reduced. Together with an appropriate optimization of several process-parameters the effective life time of the Pt-Rh catalyst could be significantly improved.

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Untersuchungen an Pt-10%Rh-Katalysatornetzen mit Hilfe von ESCA, SIMS, SEM und XRD

     

1H and 13C NMR of platinum porphyrins—II. Platinum complexes of meso-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl) porphyrin and 2,3,7,8,12,13,17,18-octaethylporphyrin

The ¹H and ¹³C NMR spectra of the title compounds are reported. In both porphyrins, long-range spin-spin coupling is observed between platinum and the porphyrin protons and carbon atoms. Two-bond Pt-“α-pyrrole” carbon couplings are less than the three-bond Pt-“fβ-pyrrole” carbon and Pt-“meso-carbon” couplings. Also, large upfield shifts of the pyrrole α-carbon resonances are noted. The coupling mechanism appears to proceed via Fermi contact through the porphyrin σ-framework for the carbons, and the π-system for the protons.     

Tuning the emission property of carbazole-caped cyclometalated platinum(II) complexes and its application for enhanced luminescent oxygen sensing

Carbazole-caped cyclometalated platinum(II) complexes aryl-R-ppyPt(acac) (where ppy = 4-phenylpyridine, acac = acetylacetonato, aryl = carbazole and R is linker) were synthesized. The carbazole group is attached to the ppy ligand via α-diketo moiety (Pt-1) and (Pt-2) or C?C single bond (Pt-3), by Sonogashira or Negishi coupling reactions. We found that the ethynylene bonds of the C^N ligands were oxidized to α-diketo or methylene-keto structure during the metalation with K₂PtCl₄. Emissions beyond 550 nm were observed for Pt-1, with electron-withdrawing α-diketo moiety attached to ppy ligand, compared to the emission at 486 nm for the parent complex ppyPt(acac). Extended phosphorescence lifetime (τ_P = 12.4 μs) and enhanced phosphorescence quantum yield (Φ_P = 66%) were observed for Pt-3 compared to ppyPt(acac) (τ_P = 2.4 μs and Φ_P = 15%), we attribute the enhanced phosphorescence property to the electron-donating carbazole substituent. With density functional theoretical calculations (DFT), we found that the carbazole moiety is involved in the HOMO (Pt-3), the α-diketo moiety is involved in the LUMO (Pt-1), thus the energy gaps between the HOMO and LUMO in both cases were decreased and red-shifted emission is expected, compared to ppyPt(acac). The different emission properties of 1,2-dione containing complexes (Pt-1 and Pt-2) and the Pt-3 were rationalized by the spin density surface analysis of the complexes. The luminescent O₂ sensing properties of these complexes were studied in solution and in polymer films, for which fast response time (3.3 s) and recovery time (3.7 s) were observed. Two-site model fitting indicated that complex Pt-3 is the most sensitive O₂ sensing material among the complexes studied herein, with quenching constant of K_SV = 0.0238 Torr^?1.     

Coordination-driven self-assembly, structures, and dynamic properties of diplatinum hexatriynediyl and butadiynediyl complexes in which the sp carbon chains are shielded by sp3 carbon chains: towards endgroup-endgroup interactions

Sequential reactions of trans-(C6F5)(p-tol3P)2Pt(C[triple chemical bond]C)3SiEt3 (PtC6SiEt3) with nBu4N+ F(-) (THF/methanol), PtCl, KPF6/tBuOK, and CuCl give trans,trans-[(C6F5){(p-tol3P)2}Pt(C[triple chemical bond]C)3Pt{(Pp-tol3)2}(C6F5)] (PtC6Pt) in 95 % yield on multigram scales. Reactions of PtC6Pt and Ar2P(CH2)mPAr2 afford substitution products trans,trans-[(C6F5){(Ar2P(CH2)mPAr2)}Pt(C[triple chemical bond]C)3Pt{(Ar2P(CH2)mPAr2)}(C6F5)] (PtC6Pt-m/Ar; m/Ar=8/p-tol, 78 %; 10/Ph, 82 %; 11/Ph, 69 %; 12/Ph, 57 %; 14/p-tol, 57 %; 14/p-C6H4-tBu, 71 %), in which the diphosphines span the square planar platinum endgroups. An analogous reaction with PEt3 gives a tetrakis PEt3 complex Pt'C6Pt' (72 %). The crystal structures of PtC6Pt, Pt'C6Pt', PtC6Pt-10/Ph, PtC6Pt-11/Ph, and PtC6Pt-14/p-tol or solvates thereof are compared. In PtC6Pt, the endgroups can avoid van der Waals contact, and define angles of 0 degrees . In PtC6Pt-14/p-tol, the sp3 chains twist around the sp chain in a chiral double-helical motif, with an endgroup/endgroup angle of 189 degrees . The sp3 chains are too short to adopt analogous conformations in the other complexes, but laterally shield the sp chain. NMR spectroscopy shows that the helical enantiomers of PtC6Pt-14/p-tol rapidly interconvert in solution at low temperature. A crystal structure of PtC4Pt shows endgroups that are in van der Waals contact and define an angle of 41 degrees . Reactions with Ar2P(CH2)8PAr2 give PtC4Pt-8/Ar (Ar=Ph, 53 %; p-tol, 87 %). Low-temperature NMR spectroscopy establish non-helical chiral conformations. Electrochemical oxidations of the diplatinum complexes are analyzed, the reversibilities of which decrease with increasing sp chain length.     

Experimental evidence of propagating waves in hydrogen oxidation on platinum-group metals (Pt,Rh, Ir)

Kinetics and Catalysis - The H2(g) + Oads reaction on nanoplanes of Pt-, Rh- and Ir-tips with a radius of ～103 Å was studied by FEM with a resolution of ～20 Å, and the...     

Catalytic synthesis of trialkyltetrahydrofurans

Summary By catalytic vapor-phase hydrogenation over Pt- C 2,3-dialkyl-5-propyltetrahydrofurans were prepared from furan alcohols.     

Assembly-enhanced triplet-triplet annihilation upconversion in the aggregation formed by Schiff-base Pt(II) complex grafting-permethyl-β-CD and 9, 10-diphenylanthracence dimer

Water-soluble triplet sensitizer with permethyl-β-cyclodextrin (PMCD) grafting on a Schiff-base Pt (II) complex (Pt-2),was synthesized to enhance the efficiency of triplet-triplet energy transfer through hostguest complexation.DPA dimer A-2 in which two DPA carboxylate were covalently linked with an alkyl chain showed an improved triplet-triplet annihilation through both intramolecular interaction and self-aggregation. Significantly improved TTA-UC emission was observed with Pt-2 and A-2 as the donor/acceptor pair.     

An ion microprobe study of the tensile failure of A Pt-Rh-W alloy

An ion microprobe has been used to identify silicon as the embrittling agent responsible for the tensile failure of a Pt-30Rh-8W alloy. Silicon was found to be segregated on the grain boundaries of the alloy, and to have a concentration gradient along them from the outer surfaces toward the interior of the sample. Operated by Union Carbide Corporation for the Energy Research and Development Administration.     

负载型铂催化剂中的载体效应

本文用程序升温热脱附法和氢氧滴定法研究了SiO₂、SiO₂·Al₂O₃、Al₂O₃、SiO₂·SnO₂和Al₂O₃·SnO₂等和Pt的相互作用,表明Pt和载体作用强弱的顺序为:Al₂O₃>SiO₂·Al₂O₃>SiO₂;发现SnO₂具有强化SiO₂和Al₂O₃载体效应的作用;提出Pt和载体相互作用较强部位可能是Pt和缺氧氧化物所形成的表面络合物--Pt-[Al₂O_x]和Pt-[SnO_x]。     

Fe3O4修饰的Pt-Ru/C纳米催化剂的制备及其在无溶剂条件下邻氯硝基苯选择性加氢的催化性能

采用浸渍法制备了一系列Pt/Ru质量比不同的Fe₃O₄修饰的Pt-Ru/Fe₃O₄/C催化剂, 运用透射电镜(TEM)、能量弥散X射线谱(EDX)、X射线光电子能谱(XPS)、X射线粉末衍射(XRD)等手段对Pt-Ru/Fe₃O₄/C一系列催化剂进行了表征, 并考察了Pt/Ru质量比不同对催化剂Pt-Ru/Fe₃O₄/C在无溶剂条件下催化邻氯硝基苯(o-CNB)选择性加氢制备邻氯苯胺(o-CAN)催化性能的影响. 研究结果表明, 催化剂的催化活性和对目标产物的选择性跟活性组分Pt、Ru比例有关. 随着Pt/Ru比例的减小, 目标产物o-CAN的选择性有所升高, 然而反应物o-CNB的转化率有所下降. 当Pt/Ru的质量比为2时, o-CNB的转化率降为76.5%, 而目标产物o-CAN的选择性仍然为100%. 与此同时, 我们还对Pt-Ru/Fe₃O₄/C催化剂高的催化活性和目标产物的高选择性可能的原因进行了分析.