Thermal isomerization of phenylazoindoles: Inversion or rotation? That is the question

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Thermal isomerization of phenylazoindoles: Inversion or rotation? That is the question

Azoheteroarenes are emerging group of photoswitches with promising properties. Transformation from the E to the Z form is performed photochemically while backreaction is usually thermal on the ground state surface. Two possible mechanisms, inversion and torsion, are modeled in this study. The gas phase calculations show the necessity of large active space and dynamical correlation for balanced description of both mechanisms, while solvent effects are clearly underestimated by continuum solvation models.


Abstract

Azoheteroarenes represent an attractive group of photochromes exhibiting a large structural variability and tunability of photoswitching characteristics. The thermal back-isomerization can proceed via inversion or rotation mechanisms, depending on the functionalization and environment. However, the distinction between the two remains a challenge for both experiment and theory. Here, four experimentally fully characterized phenylazoindoles are studied to establish the mechanism of back-reaction in solvent using density functional theory (DFT), spin-flip time-dependent (TD-)DFT, mixed-reference TD-DFT, and restricted ensemble Kohn–Sham approaches as well as CASPT2 and CCSD(T). While the inversion is consistently described by all methods, the rotation mechanism requires multireference approaches including dynamic correlation. The balanced description of both pathways becomes even more important in solvent which apparently affects the mechanism. For the present set, the range-separated functionals combined with continuum models appear to be the most consistent with experiment in terms of the substitutional and solvent effects on thermal halftimes.

Anodic Fluorination, Methoxylation, Acetoxylation, and Cyanation of Heteroatom Organic Compounds Using Boron‐Doped Diamond, GC, and Pt Electrodes

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Anodic Fluorination, Methoxylation, Acetoxylation, and Cyanation of Heteroatom Organic Compounds Using Boron-Doped Diamond, GC, and Pt Electrodes


Abstract

Various anodic substitution reactions such as fluorination, methoxylation, acetoxylation, and cyanation of heteroatom compounds containing a sulfur or nitrogen atom were comparatively studied using boron-doped diamond (BDD), Pt, and glassy carbon (GC) anodes. It was found that BDD anode is highly effective for these anodic substitution reactions similarly to Pt anode although both BDD and GC electrodes are carbon-based materials.

Excited states of aurocarbons: CASPT2 and CCSD(T) calculations of C2Au2 and C2Au4

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Excited states of aurocarbons: CASPT2 and CCSD(T) calculations of C2Au2 and C2Au4

Highly correlated single- and multi-reference wavefunction methods are used for calculations of excitation energies upon aurosubstitution in acetylene and ethylene. Lowering of excitation energies of diauroacetylene and tetraauroethylene compared with their parent acetylene and ethylene molecules is demonstrated.


Abstract

We present CASPT2 calculations of vertical excitation energies for low-lying singlet and triplet states of auroderivatives of acetylene and ethylene representing small model aurocarbons. Data are supplemented by CCSD(T) results for triplet states. All four considered species, namely linear C2Au2 molecule and three conformers of the C2Au4 molecule—Au2C2Au2 (tetraauroethylene, the analog of the parent ethylene molecule) and σ$$ \sigma $$– and π$$ \pi $$–adducts of the Au2 molecule with the auroacetylene exhibit considerable lowering of low-lying excitation energies when compared with their parent acetylene and ethylene molecules. Singlet and triplet excitation energies of diauroacetylene drop by 57% and 48%, respectively, and of tetraauroethylene, by 68% and 56% when compared with their respective parent molecules. Even more is lowered the singlet–triplet energy gap. We stress the importance of the dynamical correlation in CASPT2 calculations and discuss problems with selection of the appropriate active space in aurocarbons.