Push-pull effects and emission from ternary complexes of platinum(II), substituted terpyridines, and the strong-field cyanide ion

As part of an effort to develop new lumaphors involving late transition metal ions, this report describes the synthesis and characterization of the first platinum(II) derivatives containing 2,2':6',2'-terpyridine (trpy) and cyanide as co-ligands. According to existing models, including cyanide in the coordination sphere should raise the energies and minimize the influence of short-lived d-d excited states that otherwise compromise the excited-state lifetime. Both [Pt(trpy)(CN)]+ and the 4'-cyano-2,2':6',2'-terpyridine analogue [Pt(CN-T)(CN)]+ are emissive in dichloromethane solution, but the signals are weak. Part of the problem is that the d-pi* charge-transfer excited states also rise in energy, so that the emission actually originates from a (3)pi-pi* state with a relatively low radiative rate constant. However, another member of the series, the 4'-dimethylamino-2,2':6',2'-terpyridine (dma-T) derivative [Pt(dma-T)(CN)]+, proves to be a very promising platform with an emission quantum yield of phi= 0.26 and an excited-state lifetime of tau = 22 micros in room-temperature, deoxygenated dichloromethane solution. In the dma-T complex the electron-rich dimethylamino substituent provides the basis for an emissive, but largely ligand-based, charge-transfer excited state. The orbital parentage is such that the photoluminescence persists in donating solvents like dimethylformamide, which ordinarily quenches d-pi* excited states in complexes of this type.     

Electronic states of the CeO molecule: Absorption,emission, and laser spectroscopy

The electronic spectrum of the CeO molecule is characterized by the existence of many 0-0 bands resulting from transitions between various Ω components of excited states and the 16 lower Ω states which arise from the lowest configuration… (4f)(6s). Classical studies of rotational structure of absorption and emission spectra have been extended, and argon-ion and tunable dye (coumarin 460, rhodamine 6G, rhodamine 101) lasers have been used to excite known transitions in bands which had previously been rotationally analyzed. The resulting fluorescence spectra have been used to establish the relative energies of the lower states. By tuning the lasers to excite analyzed transitions from different known electronic states it has been possible to determine the energies of 16 low-lying states, to assign quantum numbers to 14 with certainty, and to suggest assignments for the other 2. The resulting energy level diagram of lower states is discussed and shown to correlate well with the 4f6s configuration of the Ce²⁺ ion. From the energies of the low-lying states, those of the higher excited states are calculated and in some cases new values of vibrational and rotational constants are derived.     

A Fair Allocation of County Cricket Opponents

Each team in the English County Cricket Championship plays against some other teams twice a year, and others only once. This paper describes a case study whose aim was to overcome this inherent unfairness by producing a four-year schedule of opponents which was as fair as possible, and could be easily seen to be fair, while still allowing for traditional rivalries. The schedule also needed to be satisfactory in regard to several other constraints and objectives. Various simple heuristics were used; these are described in some detail. Of particular interest is the effectiveness of a ‘local non-worsening’ approach when the objective is to find any feasible solution. This is equivalent to simulated annealing at a constant temperature of absolute zero.     

Recycling solid supports – A head-to-tail linker

The concept of a `head-to-tail linker' designed to allow the regeneration and reuse of a variety of solid supports is introduced. The synthesis of this linker, its coupling to various solid supports, its application in a number of standard solid phase reactions and resin regeneration are presented.     

Multiple-quantum NMR spectra of partially oriented indene: a new approach to estimating order in a nematic phase

Cyclic J cross polarisation (CYCLCROP) is a sensitive method for the noninvasive monitoring of (13)C distributions and fluxes. The PRAWN rotating frame Hartmann-Hahn mixing sequence ameliorates problems associated with sensitivity to Hartmann-Hahn mismatch and reduces RF power deposition. The combination of CYCLCROP with echo planar imaging (EPI) for spatial encoding of the proton detected carbon signal allows efficient use of the available signal to be made, permitting a significant improvement in the temporal resolution of any study. We report here on some initial experiments to demonstrate the feasibility of echo planar proton detected (13)C imaging using CYCLCROP based upon the PRAWN module, including the application of the technique to the measurement of transport and accumulation of (13)C-labelled sucrose in a castor bean seedling. Two methods that can be used to eliminate the effect of the J-splitting in the EP images are presented. In addition, a fast, image-based B(1) field-mapping method which may be used to quantitatively map the low frequency RF field in a dual resonant ((13)C/(1)H) probe is presented. The technique utilises the above described imaging method, permitting fully quantitative, 64x64 axial field maps to be generated in about a minute.     

Optical-optical double-resonance spectroscopy of BaO: The low-lying states

Optical-optical double-resonance (OODR) induced photoluminescence into the lowest excited electronic states of BaO—a³Σ⁺, A¹Σ⁺, b³Π, and $\text{A′}{}^1\text{Π}$—from C¹Σ⁺ is described. These low-lying states are deperturbed to obtain spectroscopic constants and potential energy curves:

     

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	$\text{a}{}^3\text{Σ}{}^{\mathrm{+}}$	$\text{A}{}^1\text{Σ}{}^{\mathrm{+}}$	$\text{b}{}^3\text{Π}$	$\text{A′}{}^1\text{Π}$
$\text{T}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	16 596(3)	16 807.345(10)	17 502.6(10)	17 619.7(2)
$\text{ω}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	469.0(7)	499.620(19)	447.62(8)	447.95(22)
$\text{ω}{}_{\mathrm{<mtext>e</mtext>}}\text{x}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	1.48(4)	1.716(8)	2.287(12)	2.139(8)
$\text{ω}{}_{\mathrm{<mtext>e</mtext>}}\text{y}{}_{\mathrm{<mtext>e</mtext>}}\text{× 10}{}^2\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$		2.14(9)		1.02(3)
$\text{B}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	0.2594(5)	0.2583908(26)	0.22426(16)	0.22385(16)
$\text{α}{}_{\mathrm{<mtext>e</mtext>}}\text{× 10}{}^3\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	1.44(5)	1.111(3)	1.18(4)	1.15(4)
$\text{γ}{}_{\mathrm{<mtext>e</mtext>}}\text{× 10}{}^6\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$		7.0(7)		?4.0(21)
$\text{R}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{A}\text{?}\text{)}$	2.1294(20)	2.133512(11)	2.2901(8)	2.2922(8)