We have examined the insertion of carbenes carrying leaving groups into the [nido-B11H13]2- dianion to form the [closo-1-CB11H12]- anion. The best procedure uses CF3SiMe3 and LiCl as the source of CF2. It is simple, convenient and scalable and proceeds with 70-90% yield. Density functional calculations have been used to develop a mechanistic proposal that accounts for the different behavior of CF2, requiring only one equivalent of base for successful conversion of Na[nido-B11H14]- to [closo-1-CB11H12]-, and CCl2 and CBr2, which require more.
A simplified version of the frontier orbital model has been applied to pairs of C2, C2v, Cs, and C1 symmetry 1,3-diphenylisobenzofuran rotamers to determine their best packing for fast singlet fission (SF). For each rotamer the square of the electronic matrix element for SF was calculated at 2.2 × 109 pair geometries and a few thousand most significant physically accessible local maxima were identified in the six-dimensional space of mutual arrangements. At these pair geometries, SF energy balance was evaluated, relative SF rate constants were approximated using Marcus theory, and the SF rate constant kSF was maximized by further optimization of the geometry of the molecular pair. The process resulted in 142, 67, 214, and 291 unique geometries for the C2, C2v, Cs, and C1 symmetry molecular pairs, respectively, predicted to be superior to the C2 symmetrized known crystal pair structure. These optimized pair geometries and their triplet biexciton binding energies are reported as targets for crystal engineering and/or covalent dimer synthesis, and as possible starting points for high-level pair geometry optimizations.
- Publikační typ
- časopisecké články MeSH
In this review we first provide an introductory description of the singlet fission phenomenon and then describe the ground and electronically excited states of the parent 1,3-diphenylisobenzofuran chromophore (1) and about a dozen of its derivatives. A discussion of singlet fission in thin polycrystalline layers of these materials follows. The highest quantum yield of triplet formation by singlet fission, 200% at 80 K, is found in one of the two known crystal modification of the parent. In the other modification and in many derivatives, excimer formation competes successfully and triplet yields are low. A description of solution photophysics of covalent dimers is described in the next section. Triplet yields are very low, but interesting phenomena are uncovered. One is an observation of a separated-charges (charge-transfer) intermediate in highly polar solvents. The other is an observation of excitation isomerism in both singlet and triplet states, where in one isomer the excitation is delocalized over both halves of the covalent dimer, whereas in the other it is localized on one of the halves. In the last section we present the operation of a simple device illustrating the use of triplets generated by singlet fission for charge separation.
- MeSH
- benzofurany chemie MeSH
- chemické modely * MeSH
- elektrony MeSH
- kvantová teorie MeSH
- rozpouštědla chemie MeSH
- Publikační typ
- časopisecké články MeSH
- přehledy MeSH
This article describes the function and possible utilization of the fluorine line in the title Institute. It also focuses on the improved procedure for the conversion of the commercial salt 1H-CB11H11 – to 1H-CB11F11 – on a gram scale.
- MeSH
- anorganická chemie metody trendy MeSH
- borany chemie MeSH
- chemické jevy * MeSH
- fluor * chemie MeSH
- halogenace * MeSH
- kyselina fluorovodíková chemie MeSH
- lidé MeSH
- molekulární zobrazování * MeSH
- nanostruktury MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- práce podpořená grantem MeSH
- MeSH
- fyzikální chemie MeSH
- Publikační typ
- biografie MeSH
- O autorovi
- Zahradník, Rudolf, 1928-2020 Autorita
