Toluene Complex Research Articles

SYNTHESIS AND PROPERTIES OF PERIPHERALLY AND NONPERIPHERALLY SUBSTITUTED ZINC AND MAGNESIUM PHTHALOCYANINES BASED ON 3/4-(4-BROMO-2-((4-METHOXYPHENYL)DIAZENYL)PHENOXY)PHTHALONITRILE

The work describes the optimization of the procedure for the synthesis of 4-bromo-2-methoxyphenyldiazenylphenol, which is used as a nucleophile in the presence of 3- and 4-nitrophthalonitriles. The resulting 3-(4-bromo-2-((4-methoxyphenyl)diazenyl)phenoxy)- and 4-(4-bromo-2-((4-methoxyphenyl)diazenyl)phenoxy)phthalonitriles were used for template condensation with magnesium or zinc acetate. Methods for isolating and purifying the synthesized compounds are described. The structure and composition were confirmed using IR, 1H NMR and electron spectroscopy. Peripheral functionalization of macrocycle by a conjugate azochromophore fragment gives molecules phthalocyanine with special optical properties. This class of phthalocyanines containing an additional chromophore system in their composition is attractive for potential use not only as pigments and dyes traditional for phthalocyanine compounds, but also as chemical sensors, dye-sensitized solar cells and photosensitizers for PDT. The resulting nitriles and phthalocyanine complexes dissolve in chloroforms, toluene, THF, and DMF. The influence of the substituent location on the spectral properties of the obtained metal complexes (Zn, Mg) in organic solvents has been studied. For non-peripherally substituted metal phthalocyanines, acid-base properties are studied. To observe and study the acid-base effect, spectrophotometric titration of the trifluoroacetic acid complex in toluene is used. It is shown that the magnesium complex is more basic than the zinc complex. In this work, the luminescent properties are also studied and the quantum yields of singlet oxygen formation for synthesized complexes in THF are determined. The influence of the substituent location on the quantum yield of fluorescence, as well as on the generation of singlet oxygen, is noted in the work.

Periphery-Core Strategy to Access a Bowl-Shaped Molecule Bearing Multiple Heteroatoms.

Most of the bowl-shaped molecules are synthesized via a core-periphery strategy with the bowl rim closed at the final stage. However, the construction of heteroatom-doped buckybowls by the periphery-core method with the bowl bottom sealed by inserting new atoms in the last step is quite limited. Herein we report the synthesis of a bowl-shaped compound containing four sulfur atoms and two embedded N-B bonds with the ratio of carbon atom and heteroatom as low as four through a periphery-core strategy. Crystallographic analysis confirms the formation of a bowl-shaped structure. The multiple heteroatoms alter the molecular electronic structure, thus resulting in the distinct aromaticity when compared with its all-carbon congener. The electron-rich buckybowl shows a strong interaction with the electron-deficient fullerene C60 by forming a 1 : 1 complex in toluene.

Periphery‐Core Strategy to Access a Bowl‐Shaped Molecule Bearing Multiple Heteroatoms

AbstractMost of the bowl‐shaped molecules are synthesized via a core‐periphery strategy with the bowl rim closed at the final stage. However, the construction of heteroatom‐doped buckybowls by the periphery‐core method with the bowl bottom sealed by inserting new atoms in the last step is quite limited. Herein we report the synthesis of a bowl‐shaped compound containing four sulfur atoms and two embedded N−B bonds with the ratio of carbon atom and heteroatom as low as four through a periphery‐core strategy. Crystallographic analysis confirms the formation of a bowl‐shaped structure. The multiple heteroatoms alter the molecular electronic structure, thus resulting in the distinct aromaticity when compared with its all‐carbon congener. The electron‐rich buckybowl shows a strong interaction with the electron‐deficient fullerene C60 by forming a 1 : 1 complex in toluene.

A lead(II) toluene complex

A well-defined intermolecular toluene complex of lead(II) supported by a pincer-type saNHC (saturated N-heterocyclic carbene) ligand was prepared through deprotonation of the bis(imidazolinium) salt with Pb[N(SiMe3)2]2 or metalation of the free carbene and subsequent salt metathesis with Tl(OTf), followed by crystallization from toluene. Combined computational and experimental results indicate that noncovalent interactions with the lead atom (σ-sss-hole type interaction, dispersion) and the diisopropylphenyl side groups of the ligand (dispersion) stabilize the complex.

Cation−π Complexes of Silver Studied with Photodissociation and Velocity-Map Imaging

Ag+(aromatic) ion-molecule complexes of benzene, toluene, or furan are generated in the gas phase by laser vaporization in a supersonic expansion. These ions are mass selected in a time-of-flight spectrometer and studied with ultraviolet laser photodissociation and photofragment imaging. UV laser excitation results in dissociative charge transfer (DCT) for these ions, producing neutral silver atom and the respective aromatic cation as the photofragments. Velocity-map imaging and slice imaging techniques are employed to investigate the kinetic energy release in these photodissociation processes. In each case, DCT produces significant kinetic energy, and evidence is also found for excitation of the internal rovibrational degrees of freedom for the molecular cations. Analysis of the kinetic energy release together with the known ionization energies of silver and the molecular ligands provides new information on the cation-π bond energies.

Rare‐Earth Metal Alkyl Complexes with 3‐Arylamido‐Functionalized Indolyl Ligands: Synthesis, Characterization and Reactivity†

Summary of main observation and conclusionA series of dinuclear rare‐earth metal alkyl complexes {[μ‐η2:η1:η1‐3‐(LNCH)(CH2SiMe3)Ind]RE(CH2SiMe3)(THF)}2 (L1 = 2‐tBuC6H4, RE = Y, Gd, Dy, Er, Yb; L2 = 2,4,6‐Me3C6H2, RE = Dy, Er; Ind = indolyl) and {[μ‐η2:η1:η1‐3‐(LNCH2)Ind]RE(CH2SiMe3)(THF)}2 (L1, RE = Y, Dy, Er, Yb; L2, RE = Er, Yb) bearing 3‐arylamido functionalized indolyl ligands having diverse bonding modes with metal ions were synthesized either by the insertion reaction of the imino group to the RE—C bond or by the alkane elimination reaction. In the preparation of above complexes, rare‐earth metal alkyl complexes [μ‐η5:η1:η1‐3‐(L2NCH)(CH2SiMe3)Ind]Gd(CH2SiMe3)(THF)}2 with a μ‐η5:η1:η1 coordination mode to the gadolinium ion and {[μ‐η3:η1:η1‐3‐(L2NCH2)Ind]Dy(CH2SiMe3)(THF)}2 with a μ‐η3:η1:η1 coordination mode to the dysprosium ion were unexpectedly isolated. The reactions of 3‐(L2N=CH)Ind with Er(CH2SiMe3)3(THF)2 at room temperature, generated a tetranuclear imino‐indolyl erbium intermediate {[μ‐η1:η1‐3‐(L2N=CH)Ind]Er(CH2SiMe3)2(THF)}4, which can transform into the amido functionalized indolyl erbium complex in hot toluene. Moreover, the reactivities of the newly synthesized ytterbium complex with N‐heterocyclic compounds were investigated, affording the corresponding products of the mixed pyridyl‐indolyl, imidazolyl‐indolyl, and ortho‐metalated complexes. The yttrium complexes showed a high regioselectivity and steroselectivity for the isoprene polymerization with 1,4‐trans selectivity up to 91.7% and 1,4‐cis selectivity up to 96.1% in the presence of cocatalysts, respectively.

Crystal structures of two charge-transfer com-plexes of benzo[1,2-c:3,4-c':5,6-c'']tri-thio-phene (D 3h -BTT).

Benzo[1,2-c:3,4-c':5,6-c'']tri-thio-phene (D 3h -BTT) is an easily prepared electron donor that readily forms charge-transfer complexes with organic acceptors. We report here two crystal structures of its charge-transfer complexes with 7,7,8,8-tetra-cyano-quinodi-methane (TCNQ) and buckminsterfullerene (C60). The D 3h -BTT·TCNQ complex, C12H6S3·C12H4N4, crystallizes with mixed layers of donors and acceptors, with an estimated degree of charge transfer at 0.09 e. In the D 3h -BTT·C60·toluene complex, C12H6S3·C60·C7H8, the central ring of BTT is 'squeezed' by the C60 mol-ecules from both faces. However, the degree of charge transfer is low. The C60 unit is disordered over two sites in a 0.766 (3):0.234 (3) ratio and was refined as a two-component inversion twin.

Mesityl(amidinato)tetrylenes as ligands in iridium(i) and iridium(iii) complexes: silicon versus germanium and simple κ1-coordination versus cyclometallation.

Reactions of the mesityl(amidinato)tetrylenes E(tBu2bzam)Mes (tBu2bzam = N,N'-bis(tert-butyl)benzamidinate; Mes = mesityl; E = Ge (1Ge), Si (1Si)) with the iridium precursors [Ir2(μ-Cl)2(η4-cod)2] (cod = 1,5-cyclooctadiene) and [Ir2Cl2(μ-Cl)2(η5-Cp*)2] (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl) at room temperature led to simple coordination of the tetrylene in the case of the germylenes ([IrCl(η4-cod){κ1Ge-Ge(tBu2bzam)Mes}] (2Ge) and [IrCl2(η5-Cp*){κ1Ge-Ge(tBu2bzam)Mes}] (3Ge), respectively, but to cyclometallated products in the case of the silylenes ([IrHCl(η4-cod){κ2C,Si-Si(tBu2bzam)CH2C6H2Me2}] (4Si) and [IrCl(η5-Cp*){κ2C,Si-Si(tBu2bzam)CH2C6H2Me2}] (5Si), respectively. While the cyclometallation of the germylene ligand of the iridium(i) complex 2Ge could not be achieved by heating this complex in toluene at 90 °C, a similar treatment of the iridium(iii) complex 3Ge led to [IrCl(η5-Cp*){κ2C,Ge-Ge(tBu2bzam)CH2C6H2Me2}] (5Ge), which is the germanium analogue of 5Si. DFT calculations have shown that the mononuclear κ1E-tetrylene iridium(i) complexes [IrCl(η4-cod){κ1E-E(tBu2bzam)Mes}] (E = Si, Ge; isolated only for E = Ge, 2Ge) should not participate as intermediates in the synthesis of the cyclometallated iridium(iii) derivatives [IrHCl(η4-cod){κ2C,E-E(tBu2bzam)(CH2C6H2Me2)}] (E = Ge, Si; isolated only for E = Si, 4Si).

Structural diversity in multinuclear tantalum polyhydrides formed via reductive hydrogenolysis of metal-carbon bonds.

Using H2 as a reducing agent, we demonstrate controlled reduction of tri- and tetramethyl tantalum bis(N-heterocyclic carbene)borate complexes to yield low-valent, multinuclear tantalum polyhydrides. Reaction of a Ta(v)Me3 complex with H2 afforded a bimetallic, hydride-bridged Ta(iv) complex. The analogous reaction of a Ta(v)Me4 complex in benzene or toluene yielded bimetallic Ta(iii) complexes in which both metals are bound to the same face of a μ-η4:η4-arene2- ligand.

Molecular interactions in the complexes of toluene with butyronitrile: A DFT approach

Density Functional Theory (DFT) has been employed to investigate the self association of butyronitrile and the heterointeractions in the 1:2 (toluene: butyronitrile) and 1:1 complexes of toluene with butyronitrile. For this investigation the B3LYP functional with Grimme's dispersion correction (D3) term and ωB97XD functionals were used. The theoretical frequency analysis shows the unsuitability of B3LYP with D3 for the present investigation. Therefore, Natural Bonding Orbital analysis was done at the functional ωB97XD. It is found through this work that only the methylene hydrogens of butyronitrile are responsible for the self association among the butyronitrile molecules. In 1:1 complex, the red shift in the butyronitrile methyl asymmetric stretching mode is not due to the active participation of this group in heterointeractions and it is solely due to the other interactions happening in its vicinity. Only the interaction (TOL)C−H⋯N(BN) is present in the complex. In 1:2 complex the butyronitrile methyl/methylene hydrogens interact with the delocalized electron cloud of toluene and the toluene hydrogens interact with the butyronitrile nitrogen. Comparison of interaction energies shows that the stability of 1:2 complex is more than that of butyronitrile dimer and 1:1 complex.

Ligand "Brackets" for Ga-Ga Bond.

The reactivity of digallane (dpp-Bian)Ga-Ga(dpp-Bian) (1) (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) toward acenaphthenequinone (AcQ), sulfur dioxide, and azobenzene was investigated. The reaction of 1 with AcQ in 1:1 molar ratio proceeds via two-electron reduction of AcQ to give (dpp-Bian)Ga(μ2-AcQ)Ga(dpp-Bian) (2), in which diolate [AcQ](2-) acts as "bracket" for the Ga-Ga bond. The interaction of 1 with AcQ in 1:2 molar ratio proceeds with an oxidation of the both dpp-Bian ligands as well as of the Ga-Ga bond to give (dpp-Bian)Ga(μ2-AcQ)2Ga(dpp-Bian) (3). At 330 K in toluene complex 2 decomposes to give compounds 3 and 1. The reaction of complex 2 with atmospheric oxygen results in oxidation of a Ga-Ga bond and affords (dpp-Bian)Ga(μ2-AcQ)(μ2-O)Ga(dpp-Bian) (4). The reaction of digallane 1 with SO2 produces, depending on the ratio (1:2 or 1:4), dithionites (dpp-Bian)Ga(μ2-O2S-SO2)Ga(dpp-Bian) (5) and (dpp-Bian)Ga(μ2-O2S-SO2)2Ga(dpp-Bian) (6). In compound 5 the Ga-Ga bond is preserved and supported by dithionite dianionic bracket. In compound 6 the gallium centers are bridged by two dithionite ligands. Both 5 and 6 consist of dpp-Bian radical anionic ligands. Four-electron reduction of azobenzene with 1 mol equiv of digallane 1 leads to complex (dpp-Bian)Ga(μ2-NPh)2Ga(dpp-Bian) (7). Paramagnetic compounds 2-7 were characterized by electron spin resonance spectroscopy, and their molecular structures were established by single-crystal X-ray analysis. Magnetic behavior of compounds 2, 5, and 6 was investigated by superconducting quantum interference device technique in the range of 2-295 K.

η(6) -Arene-Zirconium-PNP-Pincer Complexes: Mechanism of Their Hydrogenolytic Formation and Their Reactivity as Zirconium(II) Synthons.

The cyclometalated monobenzyl complexes [(Cbzdiphos(R) -CH)ZrBnX] 1 (iPr) Cl and 1 (Ph) I reacted with dihydrogen (10 bar) to yield the η(6) -toluene complexes [(Cbzdiphos(R) )Zr(η(6) -tol)X] 2 (iPr) Cl and 2 (Ph) I (cbzdiphos=1,8-bis(phosphino)-3,6-di-tert-butyl-9H-carbazole). The arene complexes were also found to be directly accessible from the triiodide [(Cbzdiphos(Ph) )ZrI3 ] through an in situ reaction with a dibenzylmagnesium reagent and subsequent hydrogenolysis, as exemplified for the η(6) -mesitylene complex [(Cbzdiphos(Ph) )Zr(η(6) -mes)I] (3 (Ph) I). The tolyl-ring in 2 (iPr) Cl adopts a puckered arrangement (fold angle 23.3°) indicating significant arene-1,4-diido character. Deuterium labeling experiments were consistent with an intramolecular reaction sequence after the initial hydrogenolysis of a Zr-C bond by a σ-bond metathesis. A DFT study of the reaction sequence indicates that hydrogenolysis by σ-bond metathesis first occurs at the cyclometalated ancillary ligand giving a hydrido-benzyl intermediate, which subsequently reductively eliminates toluene that then coordinates to the Zr atom as the reduced arene ligand. Complex 2 (Ph) I was reacted with 2,6-diisopropylphenyl isocyanide giving the deep blue, diamagnetic Zr(II) -diisocyanide complex [(Cbzdiphos(Ph) )Zr(CNDipp)2 I] (4 (Ph) I). DFT modeling of 4 (Ph) I demonstrated that the HOMO of the complex is primarily located as a "lone pair on zirconium", with some degree of back-bonding into the C≡N π* bond, and the complex is thus most appropriately described as a zirconium(II) species. Reaction of 2 (Ph) I with trimethylsilylazide (N3 TMS) and 2 (iPr) Cl with 1-azidoadamantane (N3 Ad) resulted in the formation of the imido complexes [(Cbzdiphos(R) )Zr=NR'(X)] 5 (iPr) Cl-NAd and 5 (Ph) I-NTMS, respectively. Reaction of 2 (iPr) Cl with azobenzene led to N-N bond scission giving 6 (iPr) Cl, in which one of the NPh-fragments is coupled with the carbazole nitrogen to form a central η(2) -bonded hydrazide(-1), whereas the other NPh-fragment binds to zirconium acting as an imido-ligand. Finally, addition of pyridine to 2 (iPr) Cl yielded the dark purple complex [(Cbzdiphos(iPr) )Zr(bpy)Cl] (7 (iPr) Cl) through a combination of CH-activation and C-C-coupling. The structural data and UV/Vis spectroscopic properties of 7 (iPr) Cl indicate that the bpy (bipyridine) may be regarded as a (dianionic) diamido-type ligand.

Synthesis, electrochemical and complexation studies of Zn(II) aryloxyporphyrins with fullerene C60

A new series of aryloxyporphyrins bearing benzyl and naphthyl substituents viz., ZnTBPP (1), ZnTNPP (2) and ZnONPP (3) has been synthesized and characterized by UV-vis, fluorescence and 1H NMR spectroscopic techniques and mass spectrometry. 1–3 have been utilized as donors to interact with fullerene (C[Formula: see text] acceptor to form 1:1 complex in toluene at 298 K. The subsequent investigation into quenching measurements with concomitant increase in fullerene concentration revealed effective quenching constants. The calculated association constants were in the order of 103 M[Formula: see text]. However, ZnTNPP (2) exhibited higher binding constant as compared to other analogs due to effective [Formula: see text]–[Formula: see text] interactions. ZnONPP (3) exhibited 3.4 times lower association constant than ZnTNPP (2) due to steric hindrance offered by meso-(3,5-dinapthyloxyphenyl) groups. The geometric and electronic structure of Zn(II) porphyrin-fullerene dyad was probed by DFT calculations which suggested the possibility of charge transfer from meso-aryloxyporphyrin core to fullerene C[Formula: see text].

Preparation of nacrite nanorolls and their reinforcing effect in LLDPE matrix

Nacrite nanorolls were prepared by the delamination and rolling of the platy nacrite particles and the nacrite nanorolls were melt‐compounded with LLDPE to prepare a novel Nacrite/LLDPE composite. In this method, hexylamine was intercalated into the interlayer space of methoxy‐modified nacrite precursor and the deintercalation of nacrite‐hexylamine intercalation complex in toluene resulted in the delamination and rolling of nacrite layers. The nacrite nanorolls were composed with linear low‐density polyethylene (LLDPE) to prepare a novel Nacrite/LLDPE composite. X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N2 adsorption–desorption test were used to evaluate the prepared nacrite nanorolls. The results showed that the interlayer octahedral surface of nacrite was grafted with methanol and the methoxy‐modified nacrite was intercalated with hexylamine. The deintercalation of nacrite‐hexylamine intercalation complex in toluene disturbed the orderly arrangement of nacrite layers, leading to a delamination of the layered particles and subsequent formation of aluminosilicate nanorolls. The specific surface area (SSA) and Vpor value of nacrite nanorolls reached 34.69 m2/g and 0.22 cm3/g (4.52 m2/g and 0.13 cm3/g for raw nacrite). Furthermore, the mechanical properties test confirmed that the introduction of nacrite nanorolls into LLDPE matrix could improve the tensile and tear strength. 6.4% and 6.8% higher tensile strength than the pure LLDPE were observed for Nacrite/LLDPE composite with 2 wt% and 4 wt% nacrite nanorolls filler. POLYM. COMPOS., 39:448–456, 2018. © 2016 Society of Plastics Engineers

Formation of long-lived “colored” spiroantrooxazine isomers incorporated into fluoroplast F-42 matrix in a supercritical carbon dioxide medium

It has been demonstrated that formation of isomeric “colored” merocyanine forms B and Bx of indoline spiroantrooxazine (SAO) introduced into Fluoroplast F-42 matrix from supercritical carbon dioxide (SC-CO2) depends on the volume concentration of toluene in the medium, which plays a role of an aromatic electron donor cosolvent. It also has been shown that observed dependencies of changes in the content of introduced photochrome forms, forming in the Fluoroplast F-42 matrix, can be described by a scheme which reflects the redistribution kinetics of SAO molecules between the medium (SC-CO2) and the polymer. In this case, the “blue” form B is formed by SAO molecules solvated by toluene, which localize at specific fragments of the matrix and form triple SAO/F-42/toluene complexes. The “Red” form Bx is formed under the coordination of desolvated SAO molecules, which transfer into the matrix from the SC-CO2 medium, near F-42 matrix fragments.

Gas phase double-resonance IR/UV spectroscopy of an alanine dipeptide analogue using a non-covalently bound UV-tag: observation of a folded peptide conformation in the Ac-Ala-NH2–toluene complex

The conformation-selective IR spectroscopy of the alanine dipeptide analogue Ac-Ala-NH2, a molecule deprived of a UV chromophore, has been obtained by laser double-resonance IR/UV spectroscopy, using a UV-tag (toluene) non-covalently bound to the peptide. The Ac-Ala-NH2–toluene complex, as detected through a resonant multiphoton ionisation process, is composed of a folded peptide monomer (C7 conformation) attached to the toluene molecule through an NH–π H-bond. Quantum chemistry calculations suggest that the structure of this complexed folded peptide is very similar to that of the isolated peptide, legitimating this experimental strategy for investigating the peptide structure. The population of exclusively folded peptides, in contrast to the C5/C7 conformational mixture observed on isolated monomers measured with other techniques, suggest that conformational changes might not only be induced by complexation of a single polar solvent molecule as previously reported, but also by an apolar, weakly interacting molecule like toluene.

Dinuclear palladium(I) sandwich complexes of furan and toluene

The reaction of a dinuclear palladium complex [Pd 2 (CH 3 CN) 6 ][X] 2 (X = BF 4 , PF 6 ) with excess furan afforded the sandwich-type bis-furan dinuclear palladium(I) complex [Pd 2 (μ-furan) 2 (CH 3 CN) 2 ][X] 2 . The substitutionally labile bridging furan ligands in the dipalladium sandwich complex can be readily replaced with toluene to give the bis-toluene dipalladium(I) sandwich complex [Pd 2 (μ-toluene) 2 (CH 3 CN) 2 ][X] 2 .

Synthesis, chemical characterization and nonlinear optical properties of thallium(III) phthalocyanine halide complexes

The synthesis, chemical characterization and nonlinear optical properties of a family of soluble thallium(III) phthalocyanine(Pc) halide complexes are reported. Tl(t-Bu4Pc)X (X = Cl, Br, or I) were made from 4-t-butylphthalonitrile via oxidation of a dithallium(I) phthalocyanine complex and were characterized by elemental analysis, spectroscopy (UV-vis, 1H NMR and X-ray fluorescence) and MALDI-TOF mass spectrometry. Transient white light absorption measurements of the iodo complex in toluene showed a broad band (440 – 610 nm) excited state absorption with a multiexponential decay dominated by species with lifetimes of ~4.8 ± 1 ps and > 20 ns. The ratio of the long lived excited state absorption coefficient to that of the ground state is ~100 at 500 nm. Nonlinear transmission and Z-scan experiments (532 nm, f5 optics) confirmed the above and also showed that the real part of the nonlinear refractive index is negative.

Interaction of aromatic compounds with xenon: spectroscopic and computational characterization for the cases of p-cresol and toluene.

We have investigated noncovalent interactions of two aromatic compounds (toluene and p-cresol) with Xe atoms by using infrared spectroscopy in a Ne matrix and quantum chemical calculations. The present results show that the methyl group of these molecules is a sensitive probe of the interaction with Xe. We have used the molecules with the deuterated methyl group, possessing a relatively simple spectrum, which allows us to detect characteristic vibrational shifts in the complexes, in which a Xe atom interacts with the aromatic π electron system (π structure). For the p-cresol···Xe complex, we also observed evidence of the 1:1 H-bonded structure. The amount of the H-bonded structure of the cresol···Xe complex is relatively small, which agrees with the calculated interaction energies (stronger interaction for the π structure). The bands of the 1:1 complexes of p-cresol and toluene with Xe appear at low Xe concentration and their intensities relative to the monomer bands are nearly proportional to the Xe/Ne concentration ratio. For the p-cresol-Xe system, additional OH stretching bands appear at higher Xe concentrations, which are suitable for the complexes with several Xe atoms. The π structures studied in this work can probably be formed in the case of aromatic amino acids, for which these simple aromatic compounds are useful models.

Solvatochromic fluorescence properties of pyrazine-boron complex bearing a β-iminoenolate ligand.

Pyrazine-based monoboron complexes bearing two fluorine atoms (BF2 complex) or two phenyl groups (BPh2 complex) on the boron atom were synthesized, and the fluorescence properties were investigated. The BPh2 complexes exhibited red-shifted maximum absorption and maximum fluorescence wavelengths and lower molar absorption coefficients than the corresponding BF2 complexes in n-hexane. The fluorescence quantum yields of the BPh2 complexes were higher than or comparable to the corresponding BF2 complexes owing to the relatively low nonradiative rate constants. Although the nonsubstituted and trifluoromethyl-substituted derivatives did not show solvatochromism, the dimethylamino-substituted BF2 and BPh2 complexes exhibited pronounced solvatochromism in the fluorescence spectra. Dual fluorescence was observed for the dimethylamino-substituted BF2 complex in toluene, 1,4-dioxane, and chloroform, corresponding to locally excited (LE) and twisted intramolecular charge-transfer (TICT) states.