Pavel M. Polestshuk

A Bond Path and an Attractive Ehrenfest Force Do Not Necessarily Indicate Bonding Interactions: Case Study on M2X2 (M=Li, Na, K; X=H, OH, F, Cl)

Interactions in dimers of model alkali metal derivatives M(2)X(2) (M = Li or Na or K; X = H or F, Cl, OH) are studied in the frame of the quantum theory of atoms in molecules (QTAIM) using the interacting quantum atoms approach (IQA). Contrary to opinion prevalent in QTAIM studies, the interaction between two anions linked by a bond path is demonstrated to be strongly repulsive. One may therefore say that a bond path does not necessarily indicate bonding interactions. The interactions between two anions or two cations that are not linked by a bond path are also strongly repulsive. The repulsive anion-anion and cation-cation interactions are outweighed by much stronger attractive anion-cation interactions, and the model molecules are therefore in a stable state. The attractive Ehrenfest forces (calculated in the frame of the QTAIM) acting across interatomic surfaces shared by anions in the dimers do not reflect the repulsive interactions between anions. Probable reasons of this disagreement are discussed. The force exerted on the nucleus and the electrons of a particular atom by the nucleus and the electrons of any another atom in question is proposed. It is assumed that this force unambiguously exposes whether basins of two atoms are attracted or repelled by each other in a polyatomic molecule.

Generation of Triplet Excited States via Photoinduced Electron Transfer in meso-anthra-BODIPY: Fluorogenic Response toward Singlet Oxygen in Solution and in Vitro

Heavy atom-free BODIPY-anthracene dyads (BADs) generate locally excited triplet states by way of photoinduced electron transfer (PeT), followed by recombination of the resulting charge-separated states (CSS). Subsequent quenching of the triplet states by molecular oxygen produces singlet oxygen (1O2), which reacts with the anthracene moiety yielding highly fluorescent species. The steric demand of the alkyl substituents in the BODIPY subunit defines the site of 1O2 addition. Novel bis- and tetraepoxides and bicyclic acetal products, arising from rearrangements of anthracene endoperoxides were isolated and characterized. 1O2 generation by BADs in living cells enables visualization of the dyads distribution, promising new imaging applications.

Accurate integration over atomic regions bounded by zero-flux surfaces

The approach for the integration over a region covered by zero‐flux surface is described. This approach based on the surface triangulation technique is efficiently realized in a newly developed program TWOE. The elaborated method is tested on several atomic properties including the source function. TWOE results are compared with those produced by using well‐known existing programs. Absolute errors in computed atomic properties are shown to range usually from 10−6 to 10−5 au. The demonstrative examples prove that present realization has perfect convergence of atomic properties with increasing size of angular grid and allows to obtain highly accurate data even in the most difficult cases. It is believed that the developed program can be bridgehead that allows to implement atomic partitioning of any desired molecular property with high accuracy.

Forced Bonding and QTAIM Deficiencies: A Case Study of the Nature of Interactions in He@Adamantane and the Origin of the High Metastability

Calculations within the framework of the interacting quantum atoms (IQA) approach have shown that the interactions of the helium atom with both tertiary, tC, and secondary, sC, carbon atoms in the metastable He@adamantane (He@adam) endohedral complex are bonding in nature, whereas the earlier study performed within the framework of Baders quantum theory of atoms in molecules (QTAIM) revealed that only He---tC interactions are bonding. The He---tC and He---sC bonding interactions are shown to be forced by the high pressure that the helium and carbon atoms exert upon each other in He@adam. The occurrence of a bonding interaction between the helium and sC atoms, which are not linked by a bond path, clearly shows that the lack of a bond path between two atoms does not necessarily indicate the lack of a bonding interaction, as is asserted by QTAIM. IQA calculations showed that not only the destabilization of the adamantane cage, but also a huge internal destabilization of the helium atom, contribute to the metastability of He@adam, these contributions being roughly equal. This result disproves previous opinions based on QTAIM analysis that only the destabilization of the adamantane cage accounts for the endothermicity of He@adam. Also, it was found that there is no homeomorphism of the ρ(r) and -v(r) fields of He@adam. Comparison of the IQA and QTAIM results on the interactions in He@adam exposes other deficiencies of the QTAIM approach. The reasons for the deficiencies in the QTAIM approach are analyzed.

Ad hoc methods for accurate determination of Bader's atomic boundary

In addition to the recently published triangulation method [P. M. Polestshuk, J. Comput. Chem. 34, 206 (2013)], two new highly accurate approaches, ZFSX and SINTY, for the integration over an atomic region covered by a zero-flux surface (zfs) were developed and efficiently interfaced into the TWOE program. ZFSX method was realized as three independent modules (ZFSX-1, ZFSX-3, and ZFSX-5) handling interatomic surfaces of a different complexity. Details of algorithmic implementation of ZFSX and SINTY are discussed. A special attention to an extended analysis of errors in calculations of atomic properties is paid. It was shown that uncertainties in zfs determination caused by ZFSX and SINTY approaches contribute negligibly (less than 10(-6) a.u.) to the total atomic integration errors. Moreover, the new methods are able to evaluate atomic integrals with a reasonable time and can be universally applied for the systems of any complexity. It is suggested, therefore, that ZFSX and SINTY can be regarded as benchmark methods for the computation of any Quantum Theory of Atoms in Molecules atomic property.

Control of triplet state generation in heavy atom-free BODIPY-anthracene dyads by media polarity and structural factors

A family of heavy atom-free BODIPY-anthracene dyads (BADs) exhibiting triplet excited state formation from charge-transfer states is reported. Four types of BODIPY scaffolds, different in the alkyl substitution pattern, and four anthracene derivatives have been used to access BADs. Fluorescence and intersystem crossing (ISC) in these dyads depend on donor-acceptor couplings and can be accurately controlled by substitution or media polarity. Under conditions that do not allow charge transfer (CT), the dyads exhibit fluorescence with high quantum yields. Formation of charge-transfer states triggers ISC and the formation of long-lived triplet excited states in the dyads. The excited state properties were studied by steady-state techniques and ultrafast pump-probe spectroscopy to determine the parameters of the observed processes. Structural information for various BADs was derived from single crystal X-ray structure determinations alongside DFT molecular geometry optimization, revealing the effects of mutual orientation of subunits on the photophysical properties. The calculations showed that alkyl substituents on the BODIPY destabilize CT states in the dyads, thus controlling the charge transfer between the subunits. The effect of the dyad structure on the ISC efficiency was considered at the M06-2X level of theory, and a correlation between mutual orientation of the subunits and the energy gap between singlet and triplet CT states was studied using a multireference CASSCF method.

The structure of monomeric unsolvated and weakly solvated (Me2Cu)Li and (Me2Cu)Cu

Density functional theory was used to study the structure of various isomers of (Me2Cu)Li (1), (Me2Cu)Cu (2), (Me2Cu)Li · 2Me2O (3), and (Me2Cu)Cu · 2Me2S (4) in the gas phase. Isomers of 1 and 3 were shown to be typical cuprates, whereas isomers of 2 and 4 should rather be treated as unsolvated and solvated methylcopper dimers, respectively. The reasons for the difference between structures 2, 4 and 1, 3 were considered. The energies of solvation of 1 by two dimethyl ether molecules (∼34 kcal/mol) and of 2 by two dimethyl sulfide molecules (∼36 kcal/mol) and the dissociation energies of all the compounds to the dimethylcuprate anion and the corresponding cation were calculated. The energies of solvation of 1 and 2 being almost equal, the transformation of 2 into 4 decreased the dissociation energy much more substantially than the transformation of 1 into 3.

The Nature of Metal-Metal Interactions in Dimeric Hydrides and Halides of Group 11 Elements in the Light of High Level Relativistic Calculations

The titular calculations show that charges at metal atoms M are apparently the main factor governing the nature of M⋅⋅⋅M interactions in two-nuclear coinage-metal complexes, and there are certain critical values of positive charges on M atoms, on exceeding which the pair-wise M⋅⋅⋅M interactions and/or the binding between M atoms in such complexes become repulsive despite negative formation energies of such complexes, short M-M internuclear distances, and the existence of a bond critical point (BCP) between M atoms.