Doublet Channel Research Articles

Singlet and triplet to doublet energy transfer: improving organic light-emitting diodes with radicals

Organic light-emitting diodes (OLEDs) must be engineered to circumvent the efficiency limit imposed by the 3:1 ratio of triplet to singlet exciton formation following electron-hole capture. Here we show the spin nature of luminescent radicals such as TTM-3PCz allows direct energy harvesting from both singlet and triplet excitons through energy transfer, with subsequent rapid and efficient light emission from the doublet excitons. This is demonstrated with a model Thermally-Activated Delayed Fluorescence (TADF) organic semiconductor, 4CzIPN, where reverse intersystem crossing from triplets is characteristically slow (50% emission by 1 µs). The radical:TADF combination shows much faster emission via the doublet channel (80% emission by 100 ns) than the comparable TADF-only system, and sustains higher electroluminescent efficiency with increasing current density than a radical-only device. By unlocking energy transfer channels between singlet, triplet and doublet excitons, further technology opportunities are enabled for optoelectronics using organic radicals.

Molecular and Dissociative Adsorption of Oxygen on Au-Pd Bimetallic Clusters: Role of Composition and Spin State of the Cluster.

Utilization of molecular oxygen as an oxidizing agent in industrially important reactions is the ultimate goal to design environmentally benign processes under ambient conditions. However, the high thermal stability and a large O–O dissociation barrier in O2 molecule pose a great challenge toward its successful application in the oxidative chemistry. To achieve this goal, different catalysts based on monometallic and bimetallic clusters have been developed over the years to promote binding and dissociation of molecular oxygen. The successful design of efficient metal cluster catalysis needs an in-depth knowledge of synergistic effects between different metal atoms and intrinsic catalytic mechanisms for O2 adsorption and dissociation. Here, we present a systematic theoretical investigation of reaction pathways for O2 adsorption and dissociation on Au8, Pd8, and Au8–nPdn (n = 1–7) nanoclusters in different spin states. The density functional calculations point out that the O2 dissociation barriers can be significantly reduced with the help of certain bimetallic clusters along specific spin channels. Our results particularly indicate that Au5Pd3 and Au1Pd7 show very large O2 binding energies of 1.76 and 1.69 eV, respectively. The enhanced O2 binding subsequently leads to low activation barriers of 0.98 and 1.19 eV along the doublet and quartet spin channels, respectively, without the involvement of any spin flip-over for O2 dissociation. Furthermore, the computed O2 dissociation barriers are significantly low as compared to the already reported barriers (1.95–3.65 eV) on monometallic and bimetallic Au–Ag clusters. The results provide key mechanistic insights into the interaction and dissociation of molecular oxygen with Au–Pd clusters, which can prove informative for the design of efficient catalysts for oxidative chemistry involving molecular oxygen as a reactant.

P+d→He3+γ reaction with pionless effective field theory

We study the proton radiative capture by a deuteron with the pionless effective field theory [EFT($\ensuremath{\pi}\phantom{\rule{-0.5em}{0ex}}/$)] formalism. The calculation of the $pd\ensuremath{\rightarrow}^{3}\mathrm{He}\ensuremath{\gamma}$ amplitude is considered for the incoming doublet and quartet channels leading to the formation of a $^{3}\mathrm{He}$. The strong and Coulomb scattering amplitudes for the proton-deuteron ($pd$) scattering are included in this study. In this calculation, the properly normalized $^{3}\mathrm{He}$ wave function has been used at each order. We evaluate both $M1$ and $E1$ transitions in the $pd\ensuremath{\rightarrow}^{3}\mathrm{He}\ensuremath{\gamma}$ process up to NLO. We calculate the total cross section for the $pd\ensuremath{\rightarrow}^{3}\mathrm{He}\ensuremath{\gamma}$ process based on the cluster-configuration space and compare it with the experimental data. The cross section results are presented for the incoming proton with the energy $0.5\ensuremath{\le}E\ensuremath{\le}3$ MeV where the lower and upper limits are chosen for the treatment of Coulomb effects perturbatively and the EFT($\ensuremath{\pi}\phantom{\rule{-0.5em}{0ex}}/$) breakdown scale, respectively. No three-body force is needed to renormalize observables up to NLO other than those we have introduced in the $pd$ scattering amplitudes.

Confinement Effects On Spin-Orbit Activated Interchannel Coupling

SynopsisThe spin-orbit activated interchannel coupling is a purely relativistic effect that alters the partial photoionization cross sections of spin-orbit doublet channels. Presented is an exploration of how the spin-orbit activated interchannel coupling is affected by confinement in a C60 cage.

The proton–deuteron system in pionless EFT revisited

We provide a detailed discussion of the low-energy proton–deuteron system in pionless effective field theory, considering both the spin-quartet and doublet S-wave channels. Extending and amending our previous work on the subject, we calculate the 3He–3H binding energy difference both perturbatively (using properly normalized trinucleon wave functions) and non-perturbatively by resumming all Coulomb diagrams in the doublet channel. Our nonperturbative result agrees well with a calculation that involves the full off-shell Coulomb T-matrix. Carefully examining the cutoff-dependence in the doublet channel, we present numerical evidence for a new three-nucleon counterterm being necessary at next-to-leading order if Coulomb effects are included. Indeed, such a term has recently been identified analytically. We furthermore make a case for a simplified Coulomb power counting that is consistent throughout the bound-state and scattering regimes. Finally, using a ‘partially screened’ full off-shell Coulomb T-matrix, we investigate the importance of higher-order Coulomb corrections in low-energy quartet-channel scattering.

New insight into thend→3Hγprocess at thermal energy with pionless effective field theory

We take a new look at the neutron radiative capture by a deuteron at thermal energy with the pionless effective field theory [EFT($\ensuremath{\pi}\phantom{\rule{-0.5em}{0ex}}/$)] approach. We present in detail the calculation of $nd\ensuremath{\rightarrow}$ ${}^{3}\mathrm{H}\ensuremath{\gamma}$ amplitudes for incoming doublet and quartet channels leading to the formation of a triton fully in the projection method based on the cluster-configuration space approach. In the present work, we consider all possible one-body and two-body photon interaction diagrams. In fact, additional diagrams that make significant changes in the results of the calculation of the total cross section in the $nd\ensuremath{\rightarrow}$ ${}^{3}\mathrm{H}\ensuremath{\gamma}$ process are included in this study. The properly normalized triton wave function is calculated and taken into consideration. We compare the cross section of the dominant magnetic $M1$ transition of $nd\ensuremath{\rightarrow}$${}^{3}\mathrm{H}\ensuremath{\gamma}$ up to $\text{next-to-next-to-leading}\phantom{\rule{4.pt}{0ex}}\text{order}\phantom{\rule{4.pt}{0ex}}{\text{(N}}^{2}\text{LO)}$ with the results of the previous model-dependent theoretical calculations and experimental data. The more acceptable results for cross section ${\ensuremath{\sigma}}_{\mathrm{tot}}^{(2)}=0.297\phantom{\rule{0.28em}{0ex}}(\text{LO})+0.124\phantom{\rule{0.28em}{0ex}}(\text{NLO})+0.048\phantom{\rule{0.28em}{0ex}}({\text{N}}^{2}\text{LO})=[0.469\ifmmode\pm\else\textpm\fi{}0.033]\phantom{\rule{0.222222em}{0ex}}\text{mb}$ show order by order convergence and cutoff independence. No three-body currents are needed to renormalize observables up to ${\text{N}}^{2}\text{LO}$ in this process.

The Low-Energy p–d System in Pionless EFT

We summarize results presented at the 5th Asian Pacific Conference on Few Body Problems in Physics, which was held in Seoul in August 2011. We calculate low-energy quartet and doublet channel proton–deuteron scattering in the framework of pionless effective field theory. We obtain good agreement with the available phase shift analyses. Moreover, we calculate the Coulomb contribution to the 3He–3H binding energy difference in first order perturbation theory.

Low-energyp-dscattering andHe3in pionless effective field theory

We calculate low-energy proton--deuteron scattering in the framework of pionless effective field theory. In the quartet channel, we calculate the elastic scattering phase shift up to next-to-next-to-leading order in the power counting. In the doublet channel, we perform a next-to-leading order calculation. We obtain good agreement with the available phase shift analyses down to the scattering threshold. The phase shifts in the region of non-perturbative Coulomb interactions are calculated by using an optimised integration mesh. Moreover, the Coulomb contribution to the 3He-3H binding energy difference is evaluated in first order perturbation theory. We comment on the implications of our results for the power counting of subleading three-body forces.

Dehydrogenation reactivities of bimetallic species [formula omitted] (M = Pt, Rh) with different spin multiplicities toward NH 3 in the gas phase: A density functional theory study

The dehydrogenation reactions of bimetallic species RhMCH 2 + (M = Pt, Rh) with ammonia have been investigated by carrying out density functional calculations. Equilibrium structures and energies have been determined for intermediates and transition states in these reactions. Present results show that both metal–carbene cations have the reactivity similar to that of Pt 2 CH 2 + . The variatation of spin multiplicity can further modify significantly their dehydrogenation activities with NH 3. In the reaction of RhMCH 2 + (M = Pt, Rh) with NH 3, elimination of H 2 exclusively arises from the moiety of CH 2 and no N–H bond activation of ammonia takes place. The favored dehydrogenation process occurs on the triplet state potential energy surface of RhPtCH 2 + with NH 3, followed by intersystem crossing from the triplet to the singlet states, then the Rh-mediated loss of H 2 finally yields the singlet dehydrogenating product with Gibbs free energy Δ G about −37.0 kcal mol −1 (298.15 K). In the reaction of Rh 2 CH 2 + with NH 3, the doublet channel is favorable energetically. The overall low-cost pathway has a Gibbs free energy of Δ G about −26.1 kcal mol −1 (298.15 K).

Three-body problem with short-range forces: Renormalized equations and regulator-independent results

We discuss effective field theory treatments of the problem of three particles interacting via short-range forces. One case of such a system is neutron-deuteron scattering at low energies. We demonstrate that in attractive channels the renormalization-group evolution of the 1+2 scattering amplitude may be complicated by the presence of eigenvalues greater than unity in the kernel. We also show that these eigenvalues can be removed from the kernel by one subtraction, resulting in an equation which is renormalization-group invariant. A unique solution for 1+2 scattering phase shifts is then obtained. We give an explicit demonstration of our procedure for both the case of three spinless bosons and the case of the doublet channel in nd scattering. After the contribution of the two-body effective range is included in the effective field theory, it gives a good description of the nd doublet phase shifts below deuteron breakup threshold.

Range corrections to doublet S-wave neutron–deuteron scattering

We calculate the range corrections to S-wave neutron-deuteron scattering in the doublet channel (S=1/2) to first order in r/a where a is the scattering length and r the effective range. Ultraviolet divergences appearing at this order can be absorbed into a redefinition of the leading order three-body force. The corrections to the elastic scattering amplitude below the deuteron breakup threshold are computed. Inclusion of the range corrections gives good agreement with measured scattering data and potential model calculations.

Higher partial waves in an effective field theory approach to [formula omitted] scattering

The phase shifts for the higher partial waves ( l≥1 ) in the spin quartet and doublet channel of nd scattering at centre-of-mass energies up to 15 MeV are presented at next-to-leading and next-to-next-to-leading order in an effective field theory in which pions are integrated out. As available, the results agree with both phase shift analyses and potential model calculations.

Complex, energy-independent, local potential reproducing an absorptive phase shift and a bound state.

The triton binding energy, and the partly real and partly complex neutron-deuteron doublet channel elastic scattering phase shifts, calculated by means of the exact three-body theory, are used as input in the fixed-[ital l] inverse scattering theory of Marchenko. The local potentials obtained hereby are independent of energy, and complex. Their strong imaginary part reflects the strong absorption in the doublet channel arising from the opening of the deuteron breakup channel. For total orbital angular momentum [ital l] different from zero the potentials are unique, reproducing the input phase shift in the whole energy region. For [ital l]=0 where there exists, in addition, a bound state we construct a one-parameter class of complex local potentials which are phase--binding-energy equivalent; that is, each of its members reproduces, in addition to the partly complex phase shifts, the bound state with the physical, i.e., real binding energy. Correlations between the oscilliations in the radial independence of these equivalent potentials and physical properties of the input data are established.

The occurence of a CDD singularity in the neutron-deuteron doublet scattering amplitude

It is shown that for the Amado model of elastic neutron-deuteron scattering in the s-wave doublet channel the single channel N D solution is not equivalent to the exact amplitude. Equivalence of the N/ D solution is demonstrated under the insertion of a CDD pole which simultaneously generates the triton pole and the effective range anomaly, thus establishing a link between these apparently unrelated features of the doublet amplitude.

Unitary pole expansion applied to the trinucleon problem

The unitary pole expansion of a central local potential effective in $^{1}S_{0}$ and $^{3}S_{1}$ two-nucleon states is applied to the calculation of the trinucleon bound state and the nucleon-deuteron doublet and quartet scattering lengths. An iteration method is used to solve the Faddeev equations in both cases and Pad\'e techniques used to find the scattering lengths. The convergence rate of the Pad\'e approximants is found to be good in both the doublet and quartet channels and a three-term unitary pole expansion is found to give fair agreement with the exact results for the trinucleon binding energy and the scattering lengths.[NUCLEAR REACTIONS ($d,n$), $E=0$; Calculated scattering lengths, binding energy $^{3}\mathrm{He}$. Solved Faddeev equations, Pad\'e approximants. Unitary pole expansion local two-body potential.]