The singlet-triplet splittings of chlorine-substituted methylenes and silylenes have been studied by using the ab initio generalized valence bond (GVB) dissociation-consistent configuration interaction (DCCI) method. All chlorine-substituted methylenes and silylenes have singlet ground states, with calculated singlet-triplet splittings of 6.0, 20.5, 35.8, and 55.2 kcal/mol for CHCI, CCI2, SiHCI...

The geometries and energies of the electronic states of phenyloxenium ion 1 (Ph-O(+)) were computed at the multireference CASPT2/pVTZ level of theory. Despite being isoelectronic to phenylnitrene 4, the phenyloxenium ion 1 has remarkably different energetic orderings of its electronic states. The closed-shell singlet configuration ((1)A(1)) is the ground state of the phenyloxenium ion 1, with a...

Photoinduced intra-molecular energy transfer in two ketoprofen(KP)-naproxol(NPX) diastereomers proceeds via two pathways. Very fast singlet–triplet energy transfer (k = 1.2 · 10 s ) from KP to NPX occurs for a small percentage (6%) and the major pathway is triplet–triplet energy transfer (k 3 · 10 s ). This was shown with femtosecond transient absorption spectroscopy and global and target analy...

The electronic structures and spectroscopic properties of four bisanthracene bis(dicarboxylic imide)s (M1-M4) have been investigated theoretically by using density functional theory (DFT) and its time-dependent extension (TDDFT) in view of their potential use as photosensitizers in photodynamic therapy (PDT). The optimized geometries, electronic absorption transitions, singlet-triplet energy ga...

The particle-particle random phase approximation (pp-RPA) for calculating excitation energies has been applied to diradical systems. With pp-RPA, the two nonbonding electrons are treated in a subspace configuration interaction fashion while the remaining part is described by density functional theory (DFT). The vertical or adiabatic singlet-triplet energy gaps for a variety of categories of dir...

The reactions dynamics of the dicarbon molecule C2 in the 1Sigma (g)+ singlet ground state and 3Pi(u) first excited triplet state with allene, H2CCCH2(X1A1), was investigated under single collision conditions using the crossed molecular beam approach at four collision energies between 13.6 and 49.4 kJ mol(-1). The experiments were combined with ab initio electronic structure calculations of the...

Density functional theory (UB3LYP/6-31G(d,p)) was used to determine substituent effects on the singlet-triplet-state energy gap for 21 meta-substituted phenylnitrenium ions. It was found that strongly electron-donating substituents stabilize the triplet state relative to the singlet state. With sufficiently strong meta electron donors (e.g., m,m'-diaminophenylnitrenium ion) the triplet is predi...

Under strong light conditions, long-lived chlorophyll triplets ((3)Chls) are formed, which can sensitize singlet oxygen, a species harmful to the photosynthetic apparatus of plants. Plants have developed multiple photoprotective mechanisms to quench (3)Chl and scavenge singlet oxygen in order to sustain the photosynthetic activities. The lumenal loop of light-harvesting chlorophyll a/b complex ...

The adiabatic description of molecular electronic states is based on potential energy surfaces, defined by the motion of the electrons, on which the slower nuclear motions (vibrations and rotations) occur. However, this model breaks down when relativistic effects such as the coupling between the electron spin and its orbital angular momentum (spin-orbit coupling) are taken into account. The res...

We investigate the Kondo effect in a quantum dot with almost degenerate spin-singlet and triplet states for an even number of electrons. We show that the Kondo temperature as a function of the energy difference between the states Delta reaches its maximum around Delta = 0 and decreases with increasing Delta. The Kondo effect is thus enhanced by competition between singlet and triplet states. Ou...