Hot photoluminescence of GaAs-AlGaAs multiple quantum well structures under high excitation by a single shot of 30 ps, 532 nm laser

Energy-resolved decay times and time-resolved spectra of hot photoluminescence of GaAs-AlGaAs multiple quantum well structures at 77 K under high excitation (50 MW/cm²) were measured by single shot experiments with the use of a 30 ps, 532 nm laser, a streak camera, and an optical multichannel analyzer. It was found that the transition between higher subbands (n=2 e-hh) appears and its intensity relaxes with a decay time of about 200 ps. The theoretical expression for carrier relaxation in a two-dimensional quantum well was obtained. We found that the calculated energy loss rate due to Lo-phonon scattering (10 meV/ps) is at least four times larger than the observed one (2.7 meV/ps).     

New generation of the reference interaction site model self-consistent field method: introduction of spatial electron density distribution to the solvation theory

The authors propose the new generation of the reference interaction site model self-consistent field (RISM-SCF) method for the solvation effect on the electronic structure of a solute molecule, in which the procedure proposed by Gill et al. [J. Chem. Phys. 96, 7178 (1992)] is adopted. Main improvements are the introduction of spatial electron density distribution and the removal of the grid dependency that is inherent in the original RISM-SCF. The procedure also provides very stable determination of the effective charges even if a buried atom exists in the target molecule and eventually extends the applicability of the RISM-SCF. To demonstrate the superiority of our method, sample calculations for H2O, C2H5OH, and HLi in aqueous solution are presented.     

A theoretical study on CO2 insertion into an M(bond)H bond (M = Rh and Cu)

Insertion of CO₂ into the transition metal-hydride bond of [Rh^IIIH₂(PH₃)₃]⁺, Cu^IH(PH₃)₂, and Rh^IH(PH₃)₃ was theoretically investigated with ab initio MO/MP 4, SD-CI , and CCD methods. The geometries of reactants, transition states (TS ), and products were optimized at the Hartree-Fock level, and then MP 4, SD-CI , and CCD calculations were performed on those optimized structures. The TS of the CO₂ insertion into the Cu^I(bond)H bond is the most reactantlike, while the TS of the CO₂ insertion into the Rh^III(bond)H bond is the most productlike. The activation energy (E_a) and the reaction energy (ΔE) were calculated to be 6.5 and −33.5 kcal/mol for the CO₂ insertion into the Cu¹(bond)H bond, 21.2 and −7.0 kcal/mol for the CO₂ insertion into the Rh¹(bond)H bond, and 51.3 and −1.1 kcal/mol for the Rh¹¹¹(bond)H bond at the SD-CI level, where negative ΔE represents exothermicity. These results are discussed in terms of the M(bond)H bond energy and the trans-influence of the hydride ligand. © 1996 John Wiley & Sons, Inc.     

Aurophilicity-Mediated Construction of Emissive Porous Molecular Crystals as Versatile Hosts for Liquid and Solid Guests

The first examples of porous molecular crystals that are assembled through Au⋅⋅⋅Au interactions of gold complex 1 are here reported along with their exchange properties with respect to their guest components. Single-crystal X-ray diffraction (XRD) analyses indicate that the crystal structure of 1 /CH₂Cl₂⋅pentane is based on cyclic hexamers of 1 , which are formed through six Au⋅⋅⋅Au interactions. The packing of these cyclic hexamers affords a porous architecture, in which the one-dimensional channel segment contains CH₂Cl₂ and pentane as guests. These guests can be exchanged through operationally simple methods under retention of the host framework of 1 , which furnished 1 /guest complexes with 26 different guests. A single-crystal XRD analysis of 1 /eicosane, which contains the long linear alkane eicosane (n-C₂₀H₄₂), successfully provided its accurately modeled structure within the porous material. These host–guest complexes show chromic luminescence with both blue- and redshifted emissions. Moreover, this porous organometallic material can exhibit luminescent mechanochromism through release of guests.     

Theoretical study of inverted sandwich type complexes of 4d transition metal elements: interesting similarities to and differences from 3d transition metal complexes

Inverted sandwich type complexes (ISTCs) of 4d metals, (μ-η(6):η(6)-C(6)H(6))[M(DDP)](2) (DDPH = 2-{(2,6-diisopropylphenyl)amino}-4-{(2,6-diisopropylphenyl)imino}pent-2-ene; M = Y, Zr, Nb, Mo, and Tc), were investigated with density functional theory (DFT) and MRMP2 methods, where a model ligand AIP (AIPH = (Z)-1-amino-3-imino-prop-1-ene) was mainly employed. When going to Nb (group V) from Y (group III) in the periodic table, the spin multiplicity of the ground state increases in the order singlet, triplet, and quintet for M = Y, Zr, and Nb, respectively, like 3d ISTCs reported recently. This is interpreted with orbital diagram and number of d electrons. However, the spin multiplicity decreases to either singlet or triplet in ISTC of Mo (group VI) and to triplet in ISTC of Tc (group VII), where MRMP2 method is employed because the DFT method is not useful here. These spin multiplicities are much lower than the septet of ISTC of Cr and the nonet of that of Mn. When going from 3d to 4d, the position providing the maximum spin multiplicity shifts to group V from group VII. These differences arise from the size of the 4d orbital. Because of the larger size of the 4d orbital, the energy splitting between two d(δ) orbitals of M(AIP) and that between the d(δ) and d(π) orbitals are larger in the 4d complex than in the 3d complex. Thus, when occupation on the d(δ) orbital starts, the low spin state becomes ground state, which occurs at group VI. Hence, the ISTC of Nb (group V) exhibits the maximum spin multiplicity.     

Syntheses and luminescent properties of 3,5-diphenylpyrazolato-bridged heteropolynuclear platinum complexes. The influence of chloride ligands on the emission energy revealed by the systematic replacement of chloride ligands by 3,5-dimethylpyrazolate

Heteropolynuclear Pt(II) complexes with 3,5-diphenylpyrazolate [Pt(2)Ag(4)(μ-Cl)(2)(μ-Ph(2)pz)(6)] (3), [Pt(2)Ag(2)Cl(2)(μ-Ph(2)pz)(4)(Ph(2)pzH)(2)] (4), [Pt(2)Cu(2)Cl(2)(μ-Ph(2)pz)(4)(Ph(2)pzH)(2)] (5), [Pt(2)Ag(4)(μ-Cl)(μ-Me(2)pz)(μ-Ph(2)pz)(6)] (7), and [Pt(2)Ag(4)(μ-Me(2)pz)(2)(μ-Ph(2)pz)(6)] (8) have been prepared and structurally characterized. These complexes are luminescent except for 5 in the solid state at an ambient temperature with emissions of red-orange (3), orange (4), yellow-orange (7), and green (8) light, respectively. Systematic red shift of the emission energies with the number of chloride ligands was observed for 3, 7, and 8. DFT calculations indicate that the highest occupied molecular orbital (HOMO) as well as HOMO-1 of the heterohexanuclear complexes, 3, 7, and 8, having Pt(2)Ag(4) core, mainly consist of dδ orbital of Pt(II) and π orbitals of Ph(2)pz ligands, while the lowest unoccupied molecular orbital (LUMO) of these complexes mainly consists of in-phase combination of 6p of two Pt(II) centers and 5p of four Ag(I) centers. It is likely that the emissions of 3, 7, and 8 are attributed to emissive states derived from the Pt(2)(d)/π → Pt(2)Ag(4) transitions, the emission energy of which depends on the ratio of chloride ligands to pyrazolate ligands.     

Theoretical study of 1,6-anhydrosugar formation from phenyl D-glucosides under basic condition: reasons for higher reactivity of β-anomer

Degradation of anomeric phenyl d-glucosides to levoglucosan under basic condition is theoretically studied. MP4(SDQ)//DFT(B3LYP)-computational results indicate that the degradation of phenyl α-glucoside (R(α)) occurs via the S(N)icB mechanism. In this mechanism, the oxyanion at the C6, which is formed through deprotonation of the OH group, directly attacks the anomeric carbon. On the other hand, the degradation of phenyl β-glucoside (R(β)) occurs via the S(N)icB(2) mechanism. In this mechanism, the oxyanion at the C2 attacks the anomeric carbon in a nucleophilic manner to afford 1,2-anhydride intermediate and then the oxyanion at the C6 attacks the anomeric carbon to afford levoglucosan. The activation barrier is much lower in the reaction of R(β) (ΔG(0++) = 25.6 kcal/mol and E(a) = 26.5 kcal/mol) than in the reaction of R(α) (ΔG(0++) = 38.1 kcal/mol and E(a) = 37.2 kcal/mol), which is consistent with the experimental observation that β-glucoside is generally much more reactive than the corresponding α-glucoside. The lower activation barrier of the reaction of R(β) arises from the stereoelectronic effect, which is induced by the charge transfer from the ring oxygen to the anomeric carbon, and the staggered conformation around the C1-C2 bond. When the stereoelectronic effect is absent, the degradation needs larger activation energy; for instance, the degradation of phenyl 5a-carba-β-d-glucoside (R(Cβ)) occurs with large ΔG(0++) and E(a) values like those of α-glucosides, because the methylene group of R(Cβ) does not contribute to the stereoelectronic effect. Also, the conformation around the C1-C2 bond is staggered in the transition state of the R(β) reaction but eclipsed in that of the R(α) reaction, which also leads to the larger reactivity of R(β).