A benchmark theoretical study of the electronic ground state and of the vertical and adiabatic singlet-triplet (ST) excitation energies of benzene (n=1) and n-acenes (C(4n+2)H(2n+4)) ranging from naphthalene (n=2) to heptacene (n=7) is presented, on the ground of single- and multireference calculations based on restricted or unrestricted zero-order wave functions. High-level and large scale tre...

The evolution of heterocycles from hexaazaanthracene to tetraazapentacenes led to the discovery that syn aza-substituted polyazaacenes possess unusual zwitterionic structures. One of these, 5,7-diphenyl-5H,12H-quinoxalino[2,3-b]phenazine 4, first claimed in 1898 was fully characterized, including an X-ray crystal structure. These heteroacenes have a low calculated singlet-triplet gap and have u...

A synergistic approach combining high-level multiconfigurational static calculations and full-dimensional ab initio surface hopping dynamics has been employed to gain insight into the photochemistry of endoperoxides. Electronic excitation of endoperoxides triggers two competing pathways, cycloreversion and O–O homolysis, that result in the generation of singlet oxygen and oxygen diradical rearr...

Singlet exciton fission or singlet fission (SF) is a process in which a singlet excited molecule, usually in a densely packed organic solid or in a polymer, shares its energy with a neighboring molecule in its electronic ground state, both molecules forming a pair of triplet states in a spin allowed process. SF was first proposed in 1965 to explain the delayed fluorescence in anthracene crystal...

A theoretical study of the low-lying singlet and triplet electronic states of BrONO2 is presented. Calculations of excitation energies and oscillator strengths are reported using excited-state coupled cluster response methods, as well as the complete active space self-consistent field method with the full Breit–Pauli spin-orbit operator. The calculations predict that there is only one singlet s...

Few-electron quantum dots are investigated in the regime of strong tunneling to the leads. Inelastic cotunneling is used to measure the two-electron singlet-triplet splitting above and below a magnetic field driven singlet-triplet transition. Evidence for a nonequilibrium two-electron singlet-triplet Kondo effect is presented. Cotunneling allows orbital correlations and parameters characterizin...

The effective design of dyes optimized for thermally activated delayed fluorescence (TADF) requires the precise control two tiny energies: singlet–triplet gap, which has to be maintained within thermal energy, and strength spin–orbit coupling. A subtle interplay among low-energy excited states having dominant charge-transfer local character then governs TADF efficiency, making models environmen...

We investigate the order parameter of noncentrosymmetric superconductors Li2Pd3B and Li2Pt3B via the behavior of the penetration depth lambda(T). The low-temperature penetration depth shows BCS-like behavior in Li2Pd3B, while in Li2Pt3B it follows a linear temperature dependence. We propose that broken inversion symmetry and the accompanying antisymmetric spin-orbit coupling, which admix spin-s...

The synthesis, characterization, and quantitative electronic structure modeling of multi-photon absorption properties of a neat liquid L34 (4-propyl 40-butyl diphenyl acetylene) are reported. The liquid is (linearly) transparent in the visible spectrum, but possesses large two-photon absorption (2PA) and 2PA-induced singlet and triplet excited-state absorption as measured by the Z-scan techniqu...

We investigate a series of D–A molecules consisting spiro[acridan-9,9′-fluorene] as the donor and 2-phenylenepyrimidine acceptor. In two materials, spiro center effectively electronically isolates D unit from (consequently) optically innocent yet structurally influential adamantyl side groups. third material, groups attached directly to acceptor strongly influence electronic properties. Steady-...