Vacancy control in acene blends links exothermic singlet fission to coherence

The fission of singlet excitons into triplet pairs in organic materials holds great technological promise, but the rational application of this phenomenon is hampered by a lack of understanding of its complex photophysics. Here, we use the controlled introduction of vacancies by means of spacer molecules in tetracene and pentacene thin films as a tuning parameter complementing experimental observables to identify the operating principles of different singlet fission pathways. Time-resolved spectroscopic measurements in combination with microscopic modelling enables us to demonstrate distinct scenarios, resulting from different singlet-to-triplet pair energy alignments. For pentacene, where fission is exothermic, coherent mixing between the photoexcited singlet and triplet-pair states is promoted by vibronic resonances, which drives the fission process with little sensitivity to the vacancy concentration. Such vibronic resonances do not occur for endothermic materials such as tetracene, for which we find fission to be fully incoherent; a process that is shown to slow down with increasing vacancy concentration.

Exclusive triplet electron transfer leading to long-lived radical ion-pair formation in an electron rich platinum porphyrin covalently linked to fullerene dyad

Radical ion-pair energy as high as 1.48 eV with lifetime as much as ∼1 μs, exclusively from the triplet excited state of a photosensitizer, is established in a novel donor–acceptor conjugate.

Plateaus in the Hall Resistance Curve at Filling Factors 2<ν<3

The fractional quantum Hall (FQH) states with higher Landau levels have new characters different from those with 0<ν<2. The FQH states at 2<ν<3 are examined by developing the Tao-Thouless theory. We can find a unique configuration of electrons with the minimum Coulomb energy in the Landau orbitals. Therein the electron (or hole) pairs placed in the first and second nearest Landau orbitals can transfer to all the empty (or filled) orbitals at ν0=8/3, 14/5, 7/3, 11/5, and 5/2 via the Coulomb interaction. More distant electron (or hole) pairs with the same centre position have the same total momentum. Therefore, these pairs can also transfer to all the empty (or filled) orbitals. The sum of the pair energies from these quantum transitions yields a minimum at ν=ν0. The spectrum of the pair energy takes the lowest value at ν0 and a higher value with a gap in the neighbourhood of ν0 because many transitions are forbidden at a deviated filling factor from ν0. From the theoretical result, the FQH states with ν=ν0 are stable and the plateaus appear at the specific filling factors ν0.

THE EFFECT OF SCREENED COULOMB INTERACTION ON THE OPTICAL PROPERTIES OF EuS/PbS/EuS FINITE CONFINING POTENTIAL QUANTUM WELL

We theoretically investigate excitonic effects on the optical properties of quasi-two dimensional realistic EuS/PbS/EuS finite confining potential quantum well. The strong contrast of material parameter’s across the well interfaces and the characteristic band-nonparabolicity effect of lead salt semiconductor are taken into account. In presence of medium polarization a feasibility of the screened Coulomb potential in quantum well is examined and appropriate screening radius is revealed for the first time. The screened binding energy investigated while a variational approach has been used. Depend on the realistic nanostructure specifics a monotonic decrease of the enhanced binding energy is received when in-plane carrier density/temperature ratio parameter increases. Exciton absorption spectra near the band edge within the effective-mass approximation is examined. Coulomb potential having a cutoff type is used, that efficiently represented the potential in the realistic quantum well. Screened exciton factor, which is the absorption intensity enhancement of the unbound (continuum) exciton states that are located above the band edge, is used. Plot of the dependence of the exciton factor on the exciton pair energy is given.

Condensed [OPr4]10+ and Discrete [AsO3]3–Ψ1-Tetrahedra in Pr5O4Cl[AsO3]2

The oxide chloride arsenite Pr5O4Cl[AsO3]2 was obtained as green crystals as a by-product of the synthesis of PrOTAs oxide arsenides (T = late transition metal), starting from Pr6O11, a transition metal oxide, arsenic, and an NaCl/KCl flux. Pr5O4Cl[AsO3]2 crystallizes with the monoclinic Nd5O4Cl[AsO3]2-type structure, space group C2/m. The structure was refined from single-crystal diffractometer data: a = 12.4943(15), b = 5.6884(13) c = 9.0776(19) Å , β = 116.61(1)°, R(F) = 0.0264, wR(F2) = 0.0509, 542 F2 values, and 52 variables. It is built up from corrugated layers of edge- and corner-sharing [OPr4]10+ tetrahedra, which are connected via chloride anions. The space between the layers is filled by these Cl− and discrete arsenite anions [AsO3]3− with lone pairs pointing towards each other. The network of condensed [OPr4]10+ tetrahedra is compared with the different arrays in the oxide pnictides α-PrOZnP, and in β -PrOZnP. Arsenic lone pair energy bands, main interactions, and the spatial distribution were identified precisely using density functional theory (DFT). Among the three crystallographically different sites for praseodymium, one was found non-magnetic in these calculations.