Nina P. Gritsan

Experimental and quantum chemical study of the reactions of 1,10-anthraquinones with alcohols and amines

Abstract The primary stage of the reaction between 9-aryloxy-1,10-anthraquinones and methanol is the nucleophilic 1,4-addition which gives rise to the adduct, corresponding to 1-hydroxy-9-methoxy-9-aryloxy-10-anthrone. The reaction of 9-aryloxy-1,10-anthraquinones with the primary aliphatic and aromatic amines results in the formation of 9-alkyl(aryl)amino-1,10-anthraquinones that are in a tautomeric equilibrium with 1-hydroxy-9,10-anthraquinone-9-alkyl(aryl)imines. The quantum chemical calculations of the enthalpy of 9-amine-1,10-anthraquinone isomerization are in agreement with the experimentally recorded influence on the tautomeric equilibrium of the nature of amine, solvent, and substituent in the anthraquinone nucleus. The data of quantum chemical calculations confirm the addition-elimination mechanism of the reaction of 1,10-anthraquinones with amines.

Reaction of Paramagnetic Synthon, Lithiated 4,4,5,5-Tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide, with Cyclic Aldonitrones of the Imidazole Series

It was shown that dipole-stabilized paramagnetic carbanion lithiated 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide can be attached in a nucleophilic manner to either isolated or conjugated aldonitrones of the 2,5-dihydroimidazole 3-oxide and 2H-imidazole 1-oxide series to afford adducts the subsequent oxidation of which leads to polyfunctional mono- and diradicals. According to XRD, at least two polymorphic modifications can be formed during crystallization of the resulting paramagnetic compounds, and for each of them, geometric parameters of the molecules are similar. An EPR spectrum of the diradical in frozen toluene has a complicated lineshape, which can be fairly well reproduced by using X-ray diffraction structural analysis and the following set of parameters: D=14.9 mT, E=1.7 mT; tensor a((14) N)=[0.260 0.260 1.625] mT, two equivalent tensors for the nitronyl nitroxide moiety a((14) N)=[0.198 0.198 0.700] mT, and g≈2.007. According to our DFT and ab initio calculations, the intramolecular exchange in the diradical is very weak and most likely ferromagnetic.

Photochromism of Quinoid Compounds

Abstract The paper presents the results of studies on the photochromic transformation mechanisms for three classes of quinone derivatives. Photoisomerization of the para-quinone to the anaquinone due to photochemical migration of hydrogen, aryl, or acyl groups is common to these processes. The mechanism of photochromic transformations of 1-alkyl- and 1-acyloxyanthraquinones has been investigated in detail. The primary photochemical steps of these processes - the migrations of hydrogen or an acyl group - are adiabatic photochemical reactions at the triplet potential energy surface. Variation of substituents in the anthraquinone ring, in the alkyl group of 1-alkylanthraquinones, and particularly in the acyl group of 1-acyloxyanthraquinones makes it possible to change (from several microseconds to seconds) the lifetimes of coloured photoinduced products at room temperature.

(Azulene-1,3-diyl)-bis(nitronyl nitroxide) and (Azulene-1,3-diyl)-bis(iminonitroxide) and Their Copper Complexes

In contrast to diradicals connected by alternant hydrocarbons, only a few studies on those connected by nonalternant hydrocarbons have been reported. The syntheses, structures, and magnetic properties of azulene-1,3-diyl linked bis(nitronyl nitroxide) (NN2 Az) and bis(iminonitroxide) (IN2 Az) diradicals and their Cu(hfac)2 (hfac=hexafluoroacetylacetonate) complexes were investigated. NN2 Az was shown to have an intramolecular ferromagnetic interaction with Jobs /kB =+10.0 K (H=-2JS1 ⋅S2 ) between (nitronyl nitroxide) spins, whereas IN2 Az was estimated to have a much weaker intramolecular magnetic interaction. The reactions of NN2 Az and IN2 Az with Cu(hfac)2 gave a 1:2 [{Cu(hfac)2 }2 (NN2 Az)] complex and a 1:1 [Cu(hfac)2 (IN2 Az)]⋅C6 H12 complex, respectively. [{Cu(hfac)2 }2 (NN2 Az)] showed strong intramolecular antiferromagnetic interactions (J1-Cu-R /kB ≈-800 K, J2-Cu-R /kB ≈-500 K) between the CuII spins and the coordinating NN spins, whereas [Cu(hfac)2 (IN2 Az)] exhibited a ferromagnetic exchange interaction (Jobs-Cu-R /kB =+114 K) between the CuII spin and the imino-coordinated iminonitroxide spin.

Reactions of photoinduced 9-aryloxy-1,10-anthraquinones

Abstract The reactions of ana-anthraquinones with nucleophiles have been studied in order to find the photochromic compounds with the lowest fatigue. The primary stage of the reaction between 9-aryloxy-1,10-anthraquinones and nucleophiles (water, alcohols, primary amines) is the reaction of nucleophilic 1,4-addition. The electron withdrawing substituents in the anthraquinone increase and the electron donor ones substantially decrease the reaction rate constant favouring the stability of photoinduced 1,10-anthraquinones. All the experimental data on the reactivity of ana-quinones are in a fairly well agreement with the results of AM1 calculations of the electronic properties of anaquinones.

The Design of Radical Stacks: Nitronyl-Nitroxide-Substituted Heteropentacenes

Abstract The first alkyl chain‐anchored heteropentacene, dithieno[2,3‐d;2′,3′‐d′]benzo‐[1,2‐b;3,4‐b′]dithiophene (DTmBDT), mono‐ or disubstituted with a nitronyl nitroxide group has been prepared through a cross‐coupling synthetic procedure of the corresponding dibromo‐derivative (Br2‐DTmBDT) with a nitronyl nitroxide‐2‐ide gold(I) complex. The synthesized nitroxides possess high kinetic stability, which allowed us to investigate their structure and thermal, optical, electrochemical, and magnetic properties. Single‐crystal X‐ray diffraction of both mono‐ and diradicals revealed that the nitronyl nitroxide group lies almost in the same plane as the nearest side thiophene ring. Such arrangement favors formation of edge‐to‐edge dimers, which then form close π‐stacks surrounded by interdigitating alkyl chains. Before melting, these nitronyl nitroxide radical substituted molecules undergo at least two different phase transitions (PTs): for the monoradical, PTs are reversible, accompanied by hysteresis, and occur near 13 and 83 °C; the diradical upon heating shows a reversible PT with hysteresis in the temperature range 2–11 °C and an irreversible PT near 135 °C. PTs of this type are absent in Br2‐DTmBDT. Therefore, the step‐by‐step substitution of bromine atoms by nitronyl nitroxide groups changes the structural organization of DTmBDT and induces the emergence of PTs. This knowledge may facilitate crystal engineering of π‐stacked paramagnets and related molecular spin devices.

Photochromism of Quinonfs Experimental and Quantum Chemical Study

Abstract There are three types of photochromic processes for substituted quinones. They are characterized by photoinduced isomerization of the colorless or yellow para-quinone form to the ana-quinone colored form. Photochemical hydrogen and acyl migration in photochromic 1-alkyl- and 1-acylanthraquinones is the adiabatic process occurring on the triplet potential energy surface. Quantum chemical calculations of the structure of triplet intermediates in the photochromic reactions of phenoxy quinones were performed. It was concluded, that the most preferable mechanism of photochemical phenyl migration is the non-adiabatic process with the formation of the triplet biradical spiro-form. Variation of the lifetime of photoinduced ana-quinones by the orders of magnitude was achieved by the modification of quinone structures.

CCDC 805247: Experimental Crystal Structure Determination

Related Article: E.A.Suturina, N.A.Semenov, A.V.Lonchakov, I.Yu.Bagryanskaya, Y.V.Gatilov, I.G.Irtegova, N.V.Vasilieva, E.Lork, R.Mews, N.P.Gritsan, A.V.Zibarev|2011|J.Phys.Chem.A|115|4851|doi:10.1021/jp2019523

Photochromic Reactions of 1-Alkylanthraquinones

Abstract Under irradiation of 1-alkylanthraquinones, the hydrogen atom of substituted methyl group is transferred to a periquinoid oxygen to form the corresponding 9-hydroxy-1,10-anthraquinone-1-methides. It was shown that photochemical reaction occurs through the triplet σπ-biradical. The thermal decay of photoinduced quinone-methides results from three competing parallel processes: intramolecular hydrogen transfer (a thermal back reaction), reaction with a solvent (alcohol), and oxidation by dissolved oxygen. The structure of the transient state and the activation enthalpy for the thermal reaction of hydrogen transfer have been determined quantum chemically.