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Stable crystalline complexes of Co(II) acetylacetonate [Co(II)(acac)2], trifluoacetylacetonate [Co(II)(tfac)2] and hexafluoroacetylacetonate [Co(II)(hfac)2] with triphenodioxazines (TPDOs) were synthesized and their structures studied using X-ray crystallography. In the crystal, complexes [Co(II)(tfac)2]TPDO and [Co(II)(hfac)2]TPDO form infinite ⋯N⋯Co⋯N⋯ chains featuring 1D coordination polymeric structures, whereas in the [Co(II)(acac)2]TPDO complex, the Co(acac)2 units fill only half of the possible crystallographic positions. The electron accepting trifluoro substituents in the diketonate moieties significantly enhance the thermal stability of the complexes with TPDO. Of all the complexes, only [Co(II)(hfac)2]TPDO does not dissociate into the components in solution. In all studied complexes, the Co(II) atom is in a high-spin state and has distorted octahedral surroundings. Distortion of the octahedral polyhedrons appears as axial stretching of the octahedrons along the Co–N bonds; it is due to the specific features of the crystalline structure of the metal polymeric chain in the compounds.

A new copper(II) complex (I) was obtained by the reaction of a sterically crowded 2,4-di-(tert-butyl)-9-chloro-benzo[5,6][1,4]oxazine[2,3-b]phenoxazine bridging ligand with Cu(II) hexafluoroacetylacetonate. Compound I is a quasi-one-dimensional complex in which the Cu(hfac)2 moieties are co-crystallized with the triphenodioxazine molecules through only weak Cu⋯N short intermolecular interactions (the Cu⋯N distances are 2.732 and 2.752 A). The magnetic AC susceptibility data show that in spite of the absence of zero-field splitting in the Cu(II) ion with S = 1/2, the compound demonstrates a slow magnetic relaxation behaviour at a weak applied magnetic field (HDC = 500 Oe). The EPR spectra and DC magnetic measurements show the strong axial anisotropy of the g-tensor. The temperature dependence of the relaxation time is well described by the combination of one-phonon direct and two-phonon Raman processes.

New sterically crowded quinoxalinophenoxazine derivatives containing a crown ether fragment have been synthesized and found to exhibit strong luminescence. The synthesized heteropentacenes are interesting as potential biomarkers of ion exchange processes.

New carboxyl-containing o-aminophenols and phenoxazines were synthesized by condensation of 3,5-di-(tert.-butyl)-quinone with p-aminobenzoic and anthranilic acids. Oxidative transformations of the o-aminophenols and intermediate o-iminoquinones occur with the formation of the ESR detected phenoxazinyl radicals, which furthermore transform to phenoxazines or the dimeric products emerged through the radical attack at the C1 carbon of a formed phenoxazine. Molecular structure of the dimer obtained by oxidation of methyl ester of 4-[3,5-di-(tert.-butyl)-1-(2′-hydroxyphenyl)amino]benzoic acid was X-ray determined. Reaction of 4-[3,5-di-(tert.-butyl)-1-(2′-hydroxyphenyl)amino]benzoic acid with thionyl chloride gives rise to the formation of a derivative of 2-oxido-3H-benzo[d,j][1,2,3]oxathiazol system, the structure of which was established using X-ray crystallography. Solutions of methyl-6,8-di-(tert.-butyl)-10H-phenoxazine-3-carboxylate solvents display intense fluorescence covering a broad spectral region in the range of 400–600 nm.

The redox-active bis-chelate hexacoordinate ruthenium complex 2 Ru(ONO)2 comprising two redox-active 2,4,6,8-tetrakis(tert.-butyl)-9-hydroxyphenoxazin-1-one ligands 1 was synthesized by coupling ruthenium trichloride with 1 or its thallium salt. Reduction of 2 with zinc amalgam produces its radical-anion 2a, which readily reacts with pyridine in aerobic conditions resulting in substitution of one of the tridentate hydroxyphenoxazinone ligand by three pyridine molecules and the formation of a salt of tris(pyridine)(tetra-(tert.-butyl)oxyphenoxazin-1-onate) Ru(II) cation 5. The structure of this salt was established by X-ray crystallography and its redox activity investigated using cyclic voltammetry. The mechanism of the RuIII/RuII conversion observed in this reaction was suggested based on the data of ESR, UV-Vis spectra and DFT B3LYP/6-311++G(d,p)/SDD calculations.

A facile synthesis of derivatives of a new heterocyclic 1H-cyclopenta[b]pyridine-4,5-dione system via coupling sterically crowded 3,5-di(tert-butyl)-6-nitro-1,2-benzoquinone with arylamines and acetone was developed. The reaction mechanism involving intramolecular 1,2-shift and intermolecular transfer of tert-butyl groups of the reaction intermediates was examined on the basis of DFT/B3LYP/6–311++G(d,p) (SMD) calculations.

A series of N-aryl derivatives of heteropentacyclic 12Н-quinoxaline[2,3-b]phenoxazine (QOPO) system were synthesized and spectral, luminescent, electrochemical and optoelectronic properties of the prepared compounds studied. The compounds are well soluble in nonpolar and polar solvents, absorb in the strongest emissive part of the solar spectrum and exhibit sufficiently high photostability at air conditions. The HOMO, LUMO energy levels of the obtained QOPOs were calculated by the DFT B3LYP/6–311++G(d,p) method and assessed using the electrochemical methodology. The double-layered p-n heterojunction organic solar cells constructed on the basis of QOPOs as electron donor components, bathocuproine as the exciton blocking layer and fullerene C60 as electron acceptor displayed promising values of photovoltaic (open circuit voltage and short-circuit current density) parameters.

Reaction between sterically crowded 3,5-di-(tert-butyl)-o-benzoquinone and aromatic amines occurring at the oxidative conditions and developing to the formation of compounds 8, derivatives of the pentaheterocyclic 12Н-quinoxaline[2,3-b]phenoxazine system 2 was studied. The products obtained at the intermediate stages, including di-(tert-butyl) derivatives of the tricyclic 10H-phenoxazine system: (E)-N-3Н-phenoxazin-3-ylidene-4-methoxyaniline 3, N-(aryl)-3-arylimine-3Н-phenoxazine-2-amine 4, 1-phenyl-10H-phenoxazine 5 and 1-phenyl-3H-phenoxazin-3-one 6 were preparatively isolated and their molecular structures determined by X-ray crystallography. A stable 1-phenyl-6,8-di-(tert-butyl)-10H-phenoxazine radical 7, a primary product of oxidation of 5 was prepared and characterized by the ESR spectroscopy. Compounds 8 exhibit strong red luminescence distinguished by small Stokes shifts, short fluorescent lifetimes and high quantum yields.

A series of new nonacoordinated tris-chelate lanthanide (III) complexes was prepared by the reaction of the reduced form of the tricyclic 2,4,6,8-tetrakis(tert-butyl)-9-hydroxyphenoxazin-1-one ligand with Ln(III) acetates (Ln = La, Pr, Sm, Eu, Gd, Tb, Dy, Yb). The coordination polyhedron in all complexes, the molecular structures of which were established by X-ray diffraction studies, is the tricapped trigonal prism composed by six oxygen and three nitrogen atoms of the deprotonated ligand. Electronic absorption spectra of the deeply colored complexes contain a broad long wavelength absorption band ranging from 600 to 900 nm. The values of effective magnetic moments μeff (at 300 K) were found to be equal to 1.78, 3.41, 3.50, 4.35, 7.85, 9.22 and 10.32 μB for the Sm(III), Pr(III), Eu(III), Yb(III), Gd(III), Tb(III) and Dy(III) complexes, respectively.

A strong electron-withdrawing nitro group introduced into the 6-position of 3,5-di-(tert-butyl)-1,2-benzoquinone provides for activation of the sterically blocked Michael addition reaction channel. Addition of amines to the quinone is followed by a concerted 1,2-migration of a tert-butyl group to afford derivatives of 4-amino-3-nitrocyclohexa-3,5-diene-1,2-dione system. The multistep reaction mechanism was examined using DFT computational methods.

Complex formation reaction of redox-active 2,4,6,8-tetra(tert-butyl)phenoxazin-1-one with cobalt(II) chloride leading to the dimeric adduct has been studied. UV spectroscopy studies have revealed the equilibrium of the formed adduct with dissociated form of the complex in the acetonitrile solution. In the presence of ethylene glycol, the complex formation with cobalt(II) perchlorate has afforded the high-spin trimolecular adduct. Crystal structure of the obtained adducts has been studied by means of X-ray diffraction analysis.

The six-coordinate cobalt complexes, C57H63.50N4.50O4Co (IIa), C60H69N5O4Co (IIb), C58H67N3O8Co (IIc), C56H61N5O10Co (IId), C56H63N3O6Co (IIe), C58H66N4O6Co (IIf), and C58H63N7O8Co (IIg), adducts of high-spin tetrahedral Co(II) bis(salicylaldiminates) (C29H24.50N3.50O2Co (Ia), C32H30N4O2Co (Ib), C30H28N2O6Co (Ic), C28H22N4O8Co (Id), C28H24N2O4Co (Ie), C30H27N3O4Co (If), and C30H24N6O6Co (Ig)) and redox-active 2,4,6,8-tetrakis(tert-butyl)phenoxazin-1-one (L), were synthesized and studied for structure and magnetic properties. Complexes IIa–IIg have octahedral structure (CIF files CCDC nos. 1403920 (IIf), 1403922 (IIg)) and exist in the ground low-spin state (ls-CoIII-SQ), which arises upon intramolecular single-electron redox process in the ligand–metal system. The presence of substituents of different nature in the azomethine ligands of IIa–IIg does not induce any significant changes in their magnetic properties.

A new method for the synthesis of the pentacyclic triphenodioxazines (TPDOs) involving condensation of 6,8-di-(tert-butyl)-3H-phenoxazin-3-one with o-aminophenols has been suggested and a series of sterically crowded 2,4-di-(tert-butyl)-benzo[5,6][1,4]oxazino[2,3-b]phenoxazines (TPDOs) 4 has been prepared. The compounds are well soluble in nonpolar and polar solvents, absorb in the strongest emissive part of the solar spectrum, display intense fluorescence and are characterized by excellent photostability at air conditions. X-ray diffraction study reveals planar structures of heteropentacene cores TPDOs and π-π stacking of the molecules of some of them in crystal. The energy levels of the frontier MOs of the studied TPDOs assessed using the electrochemical methodology and calculated by the DFT B3LYP/6–311++G(d,p) method lie outside the energy domain confined by TiO2 conductivity zone and redox-mediator I−/I3−, thus meeting the requirements of dyes suitable for DSSCs. ESR and electron absorption and emission spectra of radical anion and dianion of 4 appeared under reduction with a potassium mirror in THF were reported and interpreted based of the DFT calculations.

A sterically crowded 6,8-di-(tert-butyl)-3H-phenoxazin-3-one 3 was prepared by coupling 3,5-di-(tert-butyl)-o-benzoquinone with p-aminophenol. The molecular structure of 3 was established with the aid of X-ray crystallography and the redox activity studied using cyclic voltammetry and ESR spectroscopy. The reduction of 3 with a potassium mirror led to the formation of persistent radical anion 3a and dianion 3b which were characterized by their absorption and luminescence spectra.

Two six-coordinate Sn(IV) complexes, bis-[2,4,6,8-tetra-(tert-butyl)-9-oxyphenoxazinyl-1-onolate]Sn(IV) 4 and bis-[2,4,6,8-tetra-(tert-butyl)-phenoxazinyl-1-onolate]Sn(IV) dichloride 5 with redox-active tridentate 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 2 and bidentate 1-H-1-oxo-2,4,6,8-tetra(tert-butyl) phenoxazine-1-one 3 ligands were synthesized and their molecular structures determined with the use of X-ray crystallography. Electronic structures of the complexes were investigated with DFT B3LYP*/6-311++G(d,p) calculations, SQUID magnetometry and EPR spectroscopy and assigned to the biradical Sn(IV)(CatNSQ)2 and Sn(IV)(ISQ)2Cl2 electromeric forms, where (CatNSQ)2− and (ISQ)− are radical-anions formed by the ligands 2 and 3, correspondingly. Weak ferromagnetic coupling of the two paramagnetic centers was established in complex Sn(IV)(CatNSQ)2 with ligands 2, whereas in the same type complex formed by ligands 3 the coupling of the paramagnetic centers bears weak antiferromagnetic character. The calculated exchange coupling constants J for 4 and 5 (5 cm−1 and −8 cm−1, respectively) are in sufficiently good agreement with the values obtained from analysis of μeff(T) dependences (3.5 cm−1 and −1 cm−1).

A stable biradical bis-chelate complex 3, bis-[2,4,6,8-tetra-(tert-butyl)phenoxazinonato] Zn(II), based on redox-active ligands has been prepared and structurally characterized by X-ray crystallography. Lengths of the coordination Zn–O bonds are equal to 1.938 and 2.008 A and those of the intraligand C–N and C–O bonds (1.356 and 1.308 A, respectively) point to radical-anion form of the phenoxazinone ligand. Effective magnetic moment of a microcrystalline sample of 3 measured at 70 K is equal 2.53 μB, and steadily decreases to 2.39 μB upon elevation of temperature. EPR, UV–Vis measurements and DFT B3LYP∗/6-311++G(d,p) calculations show that 3 has the ground triplet electronic state characterized with weak ferromagnetic coupling of the unpaired electrons localized on the ligands.

Adducts of cobalt(II) bis(salicylaldiminates) and 2,4,6,8-tetra-tert-butylphenoxazin-1-one were synthesized and their molecular and crystal structures were determined. According to the ESR and magnetochemical data, the metal atom is in the low-spin trivalent state (CoIII) due to the intramolecular electron transfer to the redox-active ligand. In the solid state, the mixedligand complexes are stable in air for several months, but in solution at elevated temperatures they dissociate to the starting components. Such a behavior detected by the temperature dependence of the effective magnetic moment is explained by the quantum chemical DFT calculations of the energy barriers of possible valence tautomeric dynamics, whose values were found to be higher than the enthalpy of dissociation.

A series of pseudo-octahedral metal (M = Mn, Fe, Co, Ni, Cu, Zn) complexes 4 of a new redox-active ligand, 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one 3, have been synthesized, and their molecular structures determined with help of X-ray crystallography. The effective magnetic moments of complexes 4 (M = Mn, Fe, Co, and Ni) measured in the solid state and toluene solution point to the stabilization of their high-spin electronic ground states. Detailed information on the electronic structure of the complexes and their redox-isomeric forms has been obtained using density functional theory (DFT) B3LYP*/6-311++G(d,p) calculations. The energy disfavored low-spin structures of manganese, iron, and cobalt complexes have been located, and based on the computed geometries and distribution of spin densities identified as Mn(IV)[(Cat-N-SQ)](2), Fe(II)[Cat-N-BQ)](2), and Co(II)[Cat-N-BQ)](2) compounds, respectively. It has been shown that stabilization of the high-spin structures of complexes 4 (M = Mn, Fe, Co) is caused by the rigidity of the molecular framework of ligands 3 that sterically inhibits interconversions between the redox-isomeric forms of the complexes. The calculations performed on complex 4 (M = Co) predict that a suitable structural modification that might provide for stabilization of the low-spin electromeric forms and create conditions for the valence tautomeric rearrangement via stabilization of the low-spin electromer and narrowing energy gap between the low-spin ground state tautomer and the minimal energy crossing point on the intersection of the potential energy surfaces of the interconverting structures consists in the replacement of an oxygen in the oxazine ring by a bulkier sulfur atom.

Chemical and electrochemical syntheses of a series of the zinc(II) and cadmium(II) complexes were carried out on the basis of sterically hindered Schiff bases, which are the condensation products of 4,6-di-tert-butyl-2-aminophenol with the salicylaldehyde derivatives (H2L, H2L1). The structures and compositions of the synthesized binuclear complexes M2L2 and M2L21 where M = Zn(II) and Cd(II), were proved by the data of elemental analysis, IR spectroscopy, and 1H NMR spectroscopy. The structures of the Zn2L2 · 2Py and Zn2L2 · 2DMF dimers were proved by X-ray diffraction analysis. The electrochemical dissolution of zero-valence zinc and cadmium in methanol in the presence of equimolar amounts of H2L and H2L1 made it possible to isolate dimeric complexes of the corresponding metals of the composition M2L2 and M221.

The chemical and electrochemical synthesis of cobalt(II), nickel(II), and copper(II) complexes based on sterically hindered tridentate Schiff bases obtained by the coupling of 2-amino-4,6-di-tert-butylphenol with salicylaldehyde derivatives (H2L, H2L’) was performed. The resulting dinuclear complexes were characterized by elemental analysis, IR spectroscopy, and magnetochemical measurements in the 300–2 K temperature range. The structures of the dinuclear nickel(II) and copper(II) complexes with the composition Ni2L2·2AcOH·2MeOH and Cu2L2, respectively, were established by X-ray diffraction. The copper chelates are characterized by the presence of antiferromagnetic exchange interactions. The mononuclear copper(II) complexes (DMSO)bis[2-(5,7-di-tert-butyl-4-hydroxybenzoxazol-2-yl)phenolato]copper(II) and (DMF)2bis[2-(5,7-di-tert-butyl-4-hydroxybenzoxazol-2-yl)phenolato]copper(II) were isolated upon electrochemical dissolution of copper(0) and were structurally characterized.

The reaction of di(tert-butyl) derivatives of pyrocatechol with 2,6-dihydroxyaniline afforded 2,4,6,8-tetra(tert-butyl)-9-hydroxyphenoxazin-1-one. The chemical properties of the reaction product and its ability to form complexes with metal salts as the tridentate ligand were investigated. The structure of hydroxyphenoxazinone was established by X-ray diffraction.

Study of the absorption and luminescence spectra of Schiff bases derived from o-(p-tolylsulfonylamino)benzaldehyde has shown that these systems, like those derived from salicylaldehyde, are characterized by intramolecular proton transfer in the excited and ground electronic states. This process is responsible for the appearance at 77 K of fluorescence with an anomalous Stokes shift and formation of ketone structures. Unlike o-[alkyl(or aryl)iminomethyl]phenols, o-[alkyl(or aryl)iminomethyl]anilines do not give rise to acoplanarization of the ketone fragment, which could follow intramolecular proton transfer in the excited state and is responsible for fluorescence with an anomalous Stokes shift and formation of colored structures.

Under UV-irradiation (365 nm) of their solutions Schiff bases (I) undergo the oxidative photocyctization to give 2-(3′-aryl-norbomadien-2-yl)-benzo-1,3-oxazoles (II) (λmax = 337 nm, hexane), which then convert to the quadricyclane isomers (III) (λmax = 287 nm). The back thermal reaction proceeds on heating the solution (τ1/2 70°C = 2340 s). Under prolonged UV-irradiation a further (2π+2π+2π) photocyctization of the triene moiety of (II) followed by 1,5-sigmatropic migration of a hydrogen atom occurs. The resulting photoproduct (IV) possesses by an intense horescence (λII max=390nm).

Comparative findings of the experimental and quantum-chemical studies of the structures including Intramolecular H-Bond (OH N or MH N) with the endocyclic (A) and exocyclic (B) nitrogen atom have been obtained. The photochromic properties are shown only in the structures of B-type favorable for the diabatic formation of the metastable photocolored structure. The molecules of the A-type reveal the thermochromism and/or fluorescence with the Anomalous Stokes Shift.

A copper complex with 1-H-1-oxo-2,4,6,8-tetrakis(tert-butyl)phenoxazinyl free radical ligands was synthesized, and its magnetic properties and ESR spectra were measured at 77–290 K. It was shown that a ground electron state with one unpaired electron is typical of this complex at 77–290 K. The magnetoresonance parameters of this complex are characterized by ag-factor value (1.978) that is rather unusual for copper-containing compounds and by hyperfine coupling due to Cu nuclei. The considerable broadening of ESR spectral lines with increasing temperature is probably not due to the formation of a quartet state (S=3/2). A model of electron states of the compound investigated was developed in the framework of ligand field theory, which made it possible to explain the pattern of the ESR spectra, which were untypical of copper complexes.

A novel photochromic compound with NH-N intramolecular H-bond (1-p-toluenesulphonylazo- 2,4,6,8-tetrakis(tert-butyl)phenoxazine) and the corresponding model structures (1-oxo-2,4,6,8-tetrakis(tertbutyl) phenoxazine, 2,4,5,7-tetrakis (tert-butyl )-1-( veratroylazo ) phenoxazine, 2,4,5,7-tetrakis ( tert-butyl )-Nacetyl- 1-(p-toluenesulphonylazo)phenoxazine) have been synthesized and their spectral and photochemical properties are studied. The photochromic transformations observed are found to be conditioned by ESIPT (as a primary step) followed by E-Z isomerisation about N–N-bond.