Is this how bromine spiropyran salt is converted to merocyanine under UV irradiation? A look through the prism of quantum chemical calculations.

The stability of merocyanine forms formed under UV irradiation of a solution of a spiropyran salt, in which an organic part acts as a cation and a compact bromide ion as an anion, their photophysical properties, and the formation mechanism are studied in this work using time-dependent density functional theory. Theoretical calculations show that TTC and CTT are the most stable open forms (the difference in stability energies is 10.5 and 12.0 kcal mol-1 relative to the formation energy of spiropyran, respectively). The simulated absorption bands in the UV spectrum of the merocyanine forms are observed both in the UV region at 308-366 nm and in the visible region at 544-757 nm due to n → π* and π → π* type transitions. We found that the isomerisation mechanism of spiropyran into merocyanine forms includes two key stages: the ring opening to form cisoid merocyanine forms (except unstable TCC) through conical intersection and their subsequent isomerisation to form stable transoid isomers. The length of the Cspiro-O bond is 1.97 Å and the C1'-C2'-C3'-C4' angle is 70° in the structure close to conical intersection. The stage that determines the rate of this process is the isomerisation between transoid forms, as in the case of transformation of open merocyanine forms into spiropyran.

Information Entropy in Chemistry: An Overview.

Basic applications of the information entropy concept to chemical objects are reviewed. These applications deal with quantifying chemical and electronic structures of molecules, signal processing, structural studies on crystals, and molecular ensembles. Recent advances in the mentioned areas make information entropy a central concept in interdisciplinary studies on digitalizing chemical reactions, chemico-information synthesis, crystal engineering, as well as digitally rethinking basic notions of structural chemistry in terms of informatics.

First α-deuterium nitroxides; synthesis and EPR study.

Herein is reported the first preparation of stable α-deuterium nitroxides of the IAPNO family. The confirmation and characteristics of the α-deuterium nitroxides and their α-hydrogen analogues are compared and analyzed. Such α-deuterium nitroxides may find use in biology, medicine and physical chemistry.

Comment on "Fullerene-based materials for solar cell applications: design of novel acceptors for efficient polymer solar cells--a DFT study" by A. Mohajeri and A. Omidvar, Phys. Chem. Chem. Phys., 2015, 17, 22367.

Though a linear correlation has been recently reported between mean polarizabilities of the fullerene derivatives and open-circuit voltages of organic solar cells based on them, we demonstrate that there is no general dependence between these two values and some related quantities (anisotropy of polarizability and LUMO levels).

Information Entropy of Fullerenes.

The reasons for the formation of the highly symmetric C60 molecule under nonequilibrium conditions are widely discussed as it dominates over numerous similar fullerene structures. In such conditions, evolution of structure rather than energy defines the processes. We have first studied the diversity of fullerenes in terms of information entropy. Sorting 2079 structures from An Atlas of Fullerenes [ Fowler , P. W. ; Manolopoulos , D. E. An Atlas of Fullerenes ; Oxford : Clarendon , 1995 . ], we have found that the information entropies of only 14 fullerenes (<1% of the studied structures) lie between the values of C60 and C70, the two most abundant fullerenes. Interestingly, buckminsterfullerene is the only fullerene with zero information entropy, i.e., an exclusive compound among the other members of the fullerene family. Such an efficient sorting demonstrates possible relevance of information entropy to chemical processes. For this reason, we have introduced an algorithm for calculating changes in information entropy at chemical transformations. The preliminary calculations of changes in information entropy at the selected fullerene reactions show good agreement with thermochemical data.

Counting the Isomers and Estimation of Anisotropy of Polarizability of the Selected C60 and C70 Bisadducts Promising for Organic Solar Cells.

Currently, bisadducts of C60 and C70 fullerenes are widely studied as electron-acceptor materials for organic solar cells. These compounds are usually used as mixtures of the positional isomers. However, as recently shown, the separate use of the purified isomers with lowest anisotropies of polarizability may enhance solar cell output parameters. To predict the structures of the compounds appropriate for this purpose, we calculated anisotropies of polarizability of four classes of fullerene bisadducts, namely, bis-[60]PCBM, [60]OQMF, bis-[70]PCBM, and [70]OQMF (18, 16, 41, and 42 positional isomers, respectively). As found, the anisotropies quadratically correlate with the interaddend distances in fullerene bisadducts, whereas there are no obvious correlations between the structures and lowest unoccupied molecular orbital levels, traditionally used for assessing the efficiency of candidates for organic solar cell electron acceptors. According to our calculations, bisadducts bis-[60]PCBM-ee-1, [60]OQMF-cis-3.2, [60]OQMF-trans-4.2, cc(1.1)cc(2'.1)-bis-[70]PCBM, and cc1cc(2'.1)-[70]OQMF have the lowest anisotropies of polarizability. These compounds have a primary interest for synthesis, purification, and further separate testing in solar cells. The structures of these adducts have a common feature, which we describe with the "not so close and not so far" rule: the distances between the addends in the most isotropic fullerene bisaddicts should be medium among the possible values. These are ee, ef, cis-3, and trans-4 positions in the case of the C60 bisadducts and cc bonds placed on the different poles and the same hemisphere of the C70 skeleton.

Polarizability of fullerene [2+2]-dimers: a DFT study.

Currently, the exaltation of polarizability of (C60)2 dimers has been predicted with DFT-methods (D. Sh. Sabirov, RSC Adv., 2013, 3(42), 19430). It consists of an increase in the polarizability when two C60 molecules are united, forming a [2+2]-dimer. In the present work, we point attention to the bicage structures of the other fullerenes, which are promising compounds for nano-applications. We have performed the first density-functional theory study on the polarizability of fullerene [2+2]-dimers (Cn)2 (n = 20, 24, 30, 36, 50, and 70) and shown that the exaltation of polarizability is typical for all the members of the fullerenes family.

Density functional theory study on the decay of fullerenyl radicals RC60•, ROC60•, and ROOC60• (R = tert-butyl and cumyl) and polarizability of the formed fullerene dimers.

Currently, there are no comparative studies on the possible routes of decay of fullerenyl radicals. Such information is required for development of new synthetic approaches to the fullerene derivatives, obtained via radical reactions, and understanding mechanisms of oxidative destruction of fullerene-containing materials. In the present work, we have performed a theoretical study on the possible reactions of the selected fullerenyl radicals, generated in the well-known experimental systems. We consider three main routes for the radical decay: formation of fullerene bisadducts via XC60(•) + X(•) reactions, dimerization of XC60(•), and their interaction with molecular oxygen. The calculated heat effects explain the experimental regularities of fullerene radical reactions (e.g., the reversibility of the dimerization and low reactivity of fullerenyls toward molecular oxygen). We have found that the heat effects are maximal for the dimerization of ROOC60(•), so the interaction of C60 with peroxy radicals may provide more effective synthetic routes to the single-bonded C60 dimers compared to the known ones. Moreover, the exothermicity of ROO(•) addition to C60 is increased during the subsequent addition that allows reconsidering the reasons underlying C60 antioxidant activity. Additionally, polarizability and its nonadditivity of fullerene dimers XC60-C60X have been found. Guided by the calculated polarizabilities, we assume a new bistable system "fullerenyl ↔ dimer" for molecular machinery. Depending on the conditions, such a system can exist in two states differing by their response to external electric fields.

Distributed Polarizability Model for Covalently Bonded Fullerene Nanoaggregates: Origins of Polarizability Exaltation.

Polarizability exaltation is typical for (C60)n nanostructures. It relates to the ratio between the mean polarizabilities of (C60)n and C60: the first one is higher than the n-fold mean polarizability of the original fullerene. This phenomenon is used in the design of novel fullerene compounds and the understanding of its properties but still has no chemical rationalization. In the present work, we studied the distributed polarizability of (C60)2 and isomeric (C60)3 nanoaggregates with the density functional theory method. We found that polarizability exaltation increases with the size of the nanostructure and originates from the response of the sp2-hybridized carbon atoms to the external electric field. The highest contributions to the dipole polarizability of (C60)2 and (C60)3 come from the most remote atoms of the marginal fullerene cores. The sp3-hybridized carbon atoms of cyclobutane bridges negligibly contribute to the molecular property. A similar major contribution to the molecular polarizability from the marginal atoms is observed for related carbon nanostructures isomeric to (C60)2 (tubular fullerene and nanopeanut). Additionally, we discuss the analogy between the polarizability exaltation of covalently bonded (C60)n and the increase in the polarizability found in experiments on fullerene nanoclusters/films as compared with the isolated molecules.

Sonochemical synthesis of novel C60 fullerene 1,4-oxathiane derivative through the intermediate fullerene radical anion.

We have discovered a selective and efficient method for the synthesis of previously unknown 1,9-(1',4'-oxathiano)-1,9-dihydro-(C60-Ih)[5,6]fullerene, a compound with the direct attachment of the sulfur atom to the fullerene core. The method is based on the reaction of C60 with 1,2-hydroxythiols in the presence of inorganic bases in air under ultrasonication. The significance of ultrasound has been exemplified with the comparative conventional methods. The title compound has been identified with mass-(MALDI TOF/TOF), one- and two-dimensional NMR 1H and 13C (COSY, HSQC, HMBS), IR, UV-Vis spectroscopic techniques. Using the direct EPR method, we have detected radical anion C60- (g = 2.0046 and ΔH = 2 G) as a key reaction intermediate of the sonochemical reaction. Based on the experimental results and quantum chemical calculations, we have proposed a mechanism for the conversion of C60 and 2-mercaptoethanol to the C60-1,4-oxathiane adduct.