0000000000065979
AUTHOR
Josep M. Oliva
Tuning the photophysical properties of anti-B18H22: efficient intersystem crossing between excited singlet and triplet states in new 4,4'-(HS)2-anti-B18H20.
The tuning of the photophysical properties of the highly fluorescent boron hydride cluster anti-B18H22 (1), by straightforward chemical substitution to produce 4,4'-(HS)2-anti-B18H20 (2), facilitates intersystem crossing from excited singlet states to a triplet manifold. This subsequently enhances O2((1)Δg) singlet oxygen production from a quantum yield of ΦΔ ∼ 0.008 in 1 to 0.59 in 2. This paper describes the synthesis and full structural characterization of the new compound 4,4'-(HS)2-anti-B18H20 (2) and uses UV-vis spectroscopy coupled with density functional theory (DFT) and ab initio computational studies to delineate and explain its photophysical properties.
Photochemical window mechanism for controlled atom release in carborane endohedral boxes: Theoretical evidence
Abstract On the basis of high-level quantum chemical calculations, closed-cage carboranes are shown to be prospective nanoscale mass selective conveyors via a photochemical switch. A mechanism is evidenced in which stable carborane boxes with lithium as endohedral atom, Li@CB 11 H 12 , can be photoinduced to sequentially evolve opening the cage, releasing the internal atom through a window in the box structure, and closing the cage toward either ionic or neutral channels where the charge or spin of the fragments may be controlled.
Thermochromic Fluorescence from B18H20(NC5H5)2: An Inorganic–Organic Composite Luminescent Compound with an Unusual Molecular Geometry
BH(NCH) is a rare example of two conjoined boron hydride subclusters of nido and arachno geometrical character. At room temperature, solutions of BH(NCH) emit a 690 nm fluorescence. In the solid state, this emission is shifted to 620 nm and intensifies due to restriction of the rotation of the pyridine ligands. In addition, there is a thermochromicity to the fluorescence of BH(NCH). Cooling to 8 K engenders a further shift in the emission wavelength to 585 nm and a twofold increase in intensity. Immobilization in a polystyrene thin-film matrix results in an efficient absorption of pumping excitation energy at 414 nm and a 609 nm photostable fluorescence. Such fluorescence from polystyrene t…
On the Low-Lying Excited States ofsym-Triazine-Based Herbicides
We report a joint computational and luminescence study on the low-lying excited states of sym-triazines, namely, 1,3,5-triazine (1) and the ubiquitous herbicides atrazine [6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (2)] and ametryn [6-methylthio-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine (3)]. Geometrical structures, energetics, and transition and state properties of I and 2 were computed at the TD-DFT, CASSCF, and CASPT2 levels of theory. The fluorescence and phosphorescence emission spectra, lifetimes, and fluorescence quantum yields were measured for the three compounds, and from these, the energies of the lowest excited states and their corresponding radiative rates…
Quantum Chemistry of Excited States in Polyhedral Boranes
In this Chapter we describe the electronic structure of ground states and excited states of the two isomers of octadecaborane (22), anti- and syn-B18H22, and the new derivative of anti-B18H22, the polyhedral substituted borane 4,4′-(HS)2-anti-B18H20. A theoretical interpretation is given on the fluorescence of the anti-B18H22 isomer, and the non-radiative decay of the syn-B18H22 isomer, an unsolved problem since 1962. For the new derivative of anti-B18H22, substitution of hydrogen atoms in positions 4 and 4′ by SH groups allows the tuning of the photophysical properties in 4,4′-(HS)2-anti-B18H20, facilitating intersystem crossing from the excited singlet state to the triplet state.
Ab initio quantum-chemical computations of the electronic states in HgBr2 and IBr: Molecules of interest on the Earth’s atmosphere
The electronic states of atmospheric relevant molecules IBr and HgBr are reported, within the UV-Vis spectrum range (170nm≤λphoton≤600 nm) by means of the complete-active-space self-consistent field/multi-state complete-active-space second-order perturbation theory/spin-orbit restricted-active-space state-interaction (CASSCF/MS-CASPT2/SO-RASSI) quantum-chemical approach and atomic-natural-orbital relativistic-correlation-consistent (ANO-RCC) basis sets. Several analyses of the methodology were carried out in order to reach converged results and therefore to establish a highly accurate level of theory. Good agreement is found with the experimental data with errors not higher than around 0.1 …
Design of carborane molecular architectures with electronic structure computations: From endohedral and polyradical systems to multidimensional networks
11 pags, 6 figs. -- 19th International Conference on Physical Organic Chemistry (ICPOC-19) 13–18 July 2008, Santiago de Compostela, Spain
A computational study of the lowest singlet and triplet states of neutral and dianionic 1,2-substituted icosahedral and octahedralo-carboranes
This work introduces a calibrated B3LYP/6-31G(d) study on the electronic structure of singlet and triplet neutral species of 1,2-substituted icosahedral 1,2-R(2)-1,2-C(2)B(10)H(10) and octahedral 1,2-R(2)-1,2-C(2)B(4)H(4) molecules with R = {H, OH, SH, NH(2), PH(2), CH(3), SiH(3)} and their respective dianions formed by proton removal on each R group. A variety of small adiabatic singlet-triplet gaps DeltaE(ST) are obtained from these systems ranging from 2.93 eV (R = NH(2)) <or= DeltaE(ST) <or= 3.98 eV (R = SiH(3)) for the icosahedral neutrals and 1.56 eV (R = NH(2)) <or= DeltaE(ST) <or= 4.13 eV (R = SiH(3)) for the octahedral neutrals, these gaps being globally smaller for the dianionic s…
Design of carborane molecular architectures via electronic structure computations
10 pags, 9 figs
What Is the Limit of Atom Encapsulation for Icosahedral Carboranes?
The stability of endohedral carboranes X@{1,n-C2B10H12} (X = Li(+), Be(2+); n = 2, 7, 12) and X@{CB11H12(-)} (X = Li(+), Be(2+)) is studied using electronic structure calculations with the B3LYP/6-311+G(d,p) model. Our calculations suggest that all endohedral compounds are local energy minima; for the exohedral complexes X···cage, the global energy minimum always corresponds to the X atom above a triangular face of the icosahedron. In the latter the X atom is furthest apart from the carbon atoms of the cage. As opposite to exohedral {Be(2+)···cage} complexes, no global energy minima were found for exohedral complexes {Li(+)···cage} whereby a carbon atom is present in the triangular face of …
Energy landscapes in diexo and exo/endo isomers derived from Li2B12H12
Abstract In the pursuit of detecting the first endohedral polyhedral borane complex, we report a quantum-chemical computational study of energy landscapes for diexo isomers derived from Li 2 B 12 H 12 and the exo/endo isomer Li@{LiB 12 H 12 }. Geometries, electronic structure and energy barriers are computed for the interconversion between diexo isomers and the exo / endo isomer, the latter leading to a thermal injection / ejection mechanism of Li + from outside / inside the complex [LiB 12 H 12 ] − .
Distinct Photophysics of the Isomers of B18H22 Explained
The photophysics of the two isomers of octadecaborane(22), anti- and syn-B 18H 22, have been studied by UV-vis spectroscopic techniques and theoretical computational methods. In air-saturated hexane, anti-B 18H 22 shows fluorescence with a high quantum yield, Φ F = 0.97, and singlet oxygen O 2( 1Δ g) production (Φ Δ ∼ 0.008). Conversely, isomer syn-B 18H 22 shows no measurable fluorescence, instead displaying much faster, picosecond nonradiative decay of excited singlet states. Computed potential energy hypersurfaces (PEHs) for both isomers rationalize these data, pointing to a deep S 1 minimum for anti-B 18H 22 and a conical intersection (CI) between its S 0 and S 1 states that lies 0.51 e…
On the electronic structure of a dianion, a radical anion, and a neutral biradical (HB)11CCCC(BH)11 carborane dimer
Abstract The electronic structure of a neutral, a radical anion, and a dianion carborane dimer connected via an acetylenic bridge unit (HB) 11 C C C C(BH) 11 is analyzed by quantum chemical methods. Geometries, relative stabilities, and singlet–triplet gaps are determined in the neutral and dianion species for the lowest-lying singlet and triplet states and for the doublet ground state in the radical anion. As for the recently studied biradical compounds derived from o -carborane, m -carborane and p -carborane [J. Chem. Theory Comput. 4 (2008) 1338] via double hydrogen abstraction, the neutral dimeric compound displays a biradical ground-state structure in which both singlet and triplet sta…
CCDC 1514165: Experimental Crystal Structure Determination
Related Article: Michael G. S. Londesborough, Jiří Dolanský, Luis Cerdán, Kamil Lang, Tomáš Jelínek, Josep M. Oliva, Drahomír Hnyk, Daniel Roca-Sanjuán, Antonio Francés-Monerris, Jiří Martinčík, Martin Nikl, John D. Kennedy|2017|Adv. Opt. Mater.|5|1600694|doi:10.1002/adom.201600694
CCDC 912917: Experimental Crystal Structure Determination
Related Article: Vicenta Saurí, Josep M. Oliva, Drahomír Hnyk, Jonathan Bould, Jakub Braborec, Manuela Merchán, Pavel Kubát, Ivana Císařová, Kamil Lang, and Michael G. S. Londesborough|2013|Inorg.Chem.|52|9266|doi:10.1021/ic4004559