Herein we propose a general mechanism for the racemization of [n]helicenes up to n = 24. It is a concerted process for n = 4-7, but a multi-step mechanism is followed for n≥ 8, involving 2n- 14 intermediates. The changes in the barriers are a delicate consequence of the steric hindrance and the π-interactions.

The fac-[Re(CO) 3 (deeb)L] + complex (C2) where L is the (E)-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6di-tert-butylphenol ancillary ligand, which presents an intramolecular hydrogen bond, has been synthesized and characterized using UV-vis, 1 H-NMR, FT-IR, cyclic voltammetry and DFT calculations.The UV-vis absorption and emission properties have been studied at room temperature and the results were compared with TDDFT calculations including spin-orbit effects. We report an alternative synthesis route for the fac-Re(CO) 3 (deeb)Br (C1) complex where deeb = (4,4 0 -diethanoate)-2,2 0 -bpy. Besides, wehave found that the C1 shows a red shift in the emission spectrum due to the nature of the ancillary electron donating ligand, while the C2 complex shows a blue shift in the emission spectrum suggesting that the ancillary ligand L has electron withdrawing ability and the importance of the intramolecular hydrogen bond. The calculations suggest that an experimental mixed absorption band at 361 nm could be assigned to MLCT and LLCT transitions. The electron withdrawing nature of the ancillary ligand in C2 explains the electrochemical behavior, which shows the oxidation of Re I at 1.83 V and the reduction of deeb at À0.77 V. 1.44 [s, 6H, (-CH 3 )], 4.49 [m, 4H], 5.92 [s, 2H, -NH 2 ], 6.45 [d; J = 5.5 Hz; 1H], 7.28 [d; J = 1.5 Hz; 1H], 7.47 [s, 1H], 7.51 [s, 1H], 7.53 [s, 1H], 8.11 [s, 1H], 8.20 [d; J = 5.5 Hz; 2H], 8.91 [s, 2H], Scheme 1 Structures of deeb and L ligands used in this work.

A theoretical procedure, via quantum chemical computations, to elucidate the detection principle of the turn‐off luminescence mechanism of an Eu‐based Metal‐Organic Framework sensor (Eu‐MOF) selective to aniline, is accomplished. The energy transfer channels that take place in the Eu‐MOF, as well as understanding the luminescence quenching by aniline, were investigated using the well‐known and accurate multiconfigurational ab initio methods along with sTD‐DFT. Based on multireference calculations, the sensitization pathway from the ligand (antenna) to the lanthanide was assessed in detail, that is, intersystem crossing (ISC) from the S1 to the T1 state of the ligand, with subsequent energy transfer to the 5D0 state of Eu3+. Finally, emission from the 5D0 state to the 7FJ state is clearly evidenced. Otherwise, the interaction of Eu‐MOF with aniline produces a mixture of the electronic states of both systems, where molecular orbitals on aniline now appear in the active space. Consequently, a stabilization of the T1 state of the antenna is observed, blocking the energy transfer to the 5D0 state of Eu3+, leading to a non‐emissive deactivation. Finally, in this paper, it was demonstrated that the host‐guest interactions, which are not taken frequently into account by previous reports, and the employment of high‐level theoretical approaches are imperative to raise new concepts that explain the sensing mechanism associated to chemical sensors.

Shuttling rates for neutral and charged [2]rotaxanes with rigid axles varying in lengths from 7.4 to 20.3 Å were found to be independent of the length of the axle, except when the distance was short enough to allow the ring to interact with both recognition sites which provided a short-cut mechanism that significantly lowered the energy barrier.

In this work, we adopt a quantum mechanical approach based on time-dependent density functional theory (TDDFT) to study the optical and electronic properties of alizarin supported on TiO 2 nano-crystallites, as a prototypical dye-sensitized solar cell. To ensure proper alignment of the donor (alizarin) and acceptor (TiO 2 nano-crystallite) levels, static optical excitation spectra are simulated using time-dependent density functional theory in response. The ultrafast photoelectron transfer from the dye to the cluster is simulated using an explicitly time-dependent, one-electron TDDFT ansatz. The model considers the δ-pulse excitation of a single active electron localized in the dye to the complete set of energetically accessible, delocalized molecular orbitals of the dye/nano-crystallite complex. A set of quantum mechanical tools derived from the transition electronic flux density is introduced to visualize and analyze the process in real time. The evolution of the created wave packet subject to absorbing boundary conditions at the borders of the cluster reveal that, while the electrons of the aromatic rings of alizarin are heavily involved in an ultrafast charge redistribution between the carbonyl groups of the dye molecule, they do not contribute positively to the electron injection and, overall, they delay the process.

Unlike other atoms, a planar tetracoordinate fluorine atom is elusive. So far, there are no theoretical or experimental reports suggesting their existence. Herein, we introduce the first six combinations (FIn4+,...

After an exhaustive exploration of the potential energy surface of B12E- and B12E2 (E=Li-Cs) systems, it was found that, for the anionic series, a cage-type and a quasi-planar structure, very...

No abstract