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1.
Chichibabin's and Müller's hydrocarbons are classical open‐shell singlet diradicaloids but they are highly reactive. Herein we report the successful synthesis of their respective stable analogues, OxR‐2 and OxR‐3 , based on the newly developed oxindolyl radical. X‐ray crystallographic analysis on OxR‐2 reveals a planar quinoidal backbone similar to Chichibabin's hydrocarbon, in accordance with its small diradical character (y0=11.1 %) and large singlet–triplet gap (ΔES‐T=−10.8 kcal mol−1). Variable‐temperature NMR studies on OxR‐2 disclose a slow cis/trans isomerization process in solution through a diradical transition state, with a moderate energy barrier (ΔG298K=15–16 kcal mol−1). OxR‐3 exhibits a much larger diradical character (y0=80.6 %) and a smaller singlet–triplet gap (ΔES‐T=−3.5 kcal mol−1), and thus can be easily populated to paramagnetic triplet diradical. Our studies provide a new type of stable carbon‐centered monoradical and diradicaloid.  相似文献   

2.
Variable‐temperature NMR and ESR spectroscopic studies reveal that bis(dibenzo[a,i]fluorenylidene) 1 possesses a singlet ground state, 1 (S0), while the 90° twisted triplet 1 (T1) is populated to a small extent already at room temperature. Analysis of the increasing amount of paramagnetic 1 (T1) at temperatures between 300 and 500 K yields the exchange interaction Jex/h c=3351 cm−1 and a singlet–triplet energy splitting of 9.6 kcal mol−1, which is in excellent agreement with calculations (9.3 kcal mol−1 at the UKS BP86/B3LYP/revPBE level of theory). In contrast, the zero‐field splitting parameter D is very small (calculated value −0.018 cm−1) and unmeasurable.  相似文献   

3.
Low‐temperature UV‐photolysis of mesitylphosphiranes under highly anaerobic conditions leads to the formation of the triplet mesitylphosphinidene (MesP). The recorded X‐band EPR spectrum of triplet MesP and the derived zero‐field splitting parameter D =4.116 cm−1 differ significantly from those reported previously for this intermediate. New magnetic parameters of mesitylphosphinidene are discussed along with the results of DFT calculations.  相似文献   

4.
Complex multicomponent, multispin molecular system, consisting of a septet trinitrene, two quintet dinitrenes, and three triplet mononitrenes, was obtained by the photolysis of 2,4,6-triazido-3-cyano-5-fluoropyridine in solid argon. To identify these paramagnetic products, electron paramagnetic resonance spectroscopy in combination with line-shape spectral simulations and density functional theory calculations was used. The products of the photolysis was found to be triplet 2,4-diazido-3-cyano-5-fluoropyridyl-6-nitrene (DT = 1.000 cm−1, ET = 0), triplet 2,4-diazido-3-cyano-5-fluoropyridyl-2-nitrene (DT = 1.043 cm−1, ET = 0), triplet 2,6-diazido-3-cyano-5-fluoropyridyl-4-nitrene (DT = 1.128 cm−1, ET = 0 cm−1), quintet 4-azido-3-cyano-5-fluoropyridyl-2,6-dinitrene (DQ = 0.211 cm−1, EQ = 0.0532 cm−1), quintet 2-azido-3-cyano-5-fluoropyridyl-4,6-dinitrene (DQ = 0.208 cm−1, EQ = 0.0386 cm−1), and septet 3-cyano-5-fluoropyridyl-2,4,6-trinitrene (DS = −0.1017 cm−1, ES = −0.0042 cm−1) in a 38:4:7:22:14:4 ratio, respectively.  相似文献   

5.
The kinetics of the reactions of ethene and propene with triplet oxygen atoms have been studied over a wide temperature range, T = 230–900 K, using a low‐pressure (P = 1 Torr) flow tube reactor coupled with an electron impact ionization quadrupole mass spectrometer: O + C2H4 → products (1) and O + C3H6 → products (2). The rate constants of the title reactions were determined under pseudo–first‐order conditions, either monitoring the kinetics of O‐atom consumption in excess of alkene or alkene loss in excess of oxygen atoms. The temperature dependence of the rate constant of reaction (1), k 1 = 8.64 × 10−17 T 1.70 exp(–206/T ) cm3 molecule−1 s−1 (uncertainty of 20%), was found to be in excellent agreement with multiple previous data that can be considered as a validation of the experimental approach. The measurements of the rate constant of the reaction of O atoms with propene, k 2 = 3.65 × 10−18 T 2.20 exp(455/T ) cm3 molecule−1 s−1 (uncertainty of 20%), allowed to harmonize the results of previous low‐ and high‐temperature measurements and to recommend the expression for k 2 in a wide temperature range, 200–1200 K.  相似文献   

6.
Intersystem crossing (ISC) of triplet photosensitizers is a vital process for fundamental photochemistry and photodynamic therapy (PDT). Herein, we report the co-existence of efficient ISC and long triplet excited lifetime in a heavy atom-free bodipy helicene molecule. Via theoretical computation and time-resolved EPR spectroscopy, we confirmed that the ISC of the bodipy results from its twisted molecular structure and reduced symmetry. The twisted bodipy shows intense long wavelength absorption (ϵ=1.76×105 m −1 cm−1 at 630 nm), satisfactory triplet quantum yield (ΦT=52 %), and long-lived triplet state (τT=492 μs), leading to unprecedented performance as a triplet photosensitizer for PDT. Moreover, nanoparticles constructed with such helical bodipy show efficient PDT-mediated antitumor immunity amplification with an ultra-low dose (0.25 μg kg−1), which is several hundred times lower than that of the existing PDT reagents.  相似文献   

7.
Cyclometalated IrIII complexes with acetylide ppy and bpy ligands were prepared (ppy=2‐phenylpyridine, bpy=2,2′‐bipyridine) in which naphthal ( Ir‐2 ) and naphthalimide (NI) were attached onto the ppy ( Ir‐3 ) and bpy ligands ( Ir‐4 ) through acetylide bonds. [Ir(ppy)3] ( Ir‐1 ) was also prepared as a model complex. Room‐temperature phosphorescence was observed for the complexes; both neutral and cationic complexes Ir‐3 and Ir‐4 showed strong absorption in the visible range (ε=39600 M ?1 cm?1 at 402 nm and ε=25100 M ?1 cm?1 at 404 nm, respectively), long‐lived triplet excited states (τT=9.30 μs and 16.45 μs) and room‐temperature red emission (λem=640 nm, Φp=1.4 % and λem=627 nm, Φp=0.3 %; cf. Ir‐1 : ε=16600 M ?1 cm?1 at 382 nm, τem=1.16 μs, Φp=72.6 %). Ir‐3 was strongly phosphorescent in non‐polar solvent (i.e., toluene), but the emission was completely quenched in polar solvents (MeCN). Ir‐4 gave an opposite response to the solvent polarity, that is, stronger phosphorescence in polar solvents than in non‐polar solvents. Emission of Ir‐1 and Ir‐2 was not solvent‐polarity‐dependent. The T1 excited states of Ir‐2 , Ir‐3 , and Ir‐4 were identified as mainly intraligand triplet excited states (3IL) by their small thermally induced Stokes shifts (ΔEs), nanosecond time‐resolved transient difference absorption spectroscopy, and spin‐density analysis. The complexes were used as triplet photosensitizers for triplet‐triplet annihilation (TTA) upconversion and quantum yields of 7.1 % and 14.4 % were observed for Ir‐2 and Ir‐3 , respectively, whereas the upconversion was negligible for Ir‐1 and Ir‐4 . These results will be useful for designing visible‐light‐harvesting transition‐metal complexes and for their applications as triplet photosensitizers for photocatalysis, photovoltaics, TTA upconversion, etc.  相似文献   

8.
A series of bis[N,N‐di‐(4‐methoxylphenyl)amino]arene dications 1 2+– 3 2+ have been synthesized and characterized. Their electronic structures were investigated by various experiments assisted by theoretical calculations. It was found that they are singlets in the ground state and that their diradical character is dependent on the bridging moiety. 3 2+ has a smaller singlet–triplet energy gap and its excited triplet state is thermally readily accessible. The work provides a nitrogen analogue of Thiele’s hydrocarbon with considerable diradical character.  相似文献   

9.
We report the synthesis of the novel heterometallic complex [Fe3Cr(L)2(dpm)6]?Et2O ( Fe3CrPh ) (Hdpm=dipivaloylmethane, H3L=2‐hydroxymethyl‐2‐phenylpropane‐1,3‐diol), obtained by replacing the central iron(III) atom by a chromium(III) ion in an Fe4 propeller‐like single‐molecule magnet (SMM). Structural and analytical data, high‐frequency EPR (HF‐EPR) and magnetic studies indicate that the compound is a solid solution of chromium‐centred Fe3Cr (S=6) and Fe4 (S=5) species in an 84:16 ratio. Although SMM behaviour is retained, the |D| parameter is considerably reduced as compared with the corresponding tetra‐iron(III) propeller (D=?0.179 vs. ?0.418 cm?1), and results in a lower energy barrier for magnetisation reversal (Ueff/kB=7.0 vs. 15.6 K). The origin of magnetic anisotropy in Fe3CrPh has been fully elucidated by preparing its Cr‐ and Fe‐doped Ga4 analogues, which contain chromium(III) in the central position (c) and iron(III) in two magnetically distinct peripheral sites (p1 and p2). According to HF‐EPR spectra, the Cr and Fe dopants have hard‐axis anisotropies with Dc=0.470(5) cm?1, Ec=0.029(1) cm?1, Dp1=0.710(5) cm?1, Ep1=0.077(3) cm?1, Dp2=0.602(5) cm?1, and Ep2=0.101(3) cm?1. Inspection of projection coefficients shows that contributions from dipolar interactions and from the central chromium(III) ion cancel out almost exactly. As a consequence, the easy‐axis anisotropy of Fe3CrPh is entirely due to the peripheral, hard‐axis‐type iron(III) ions, the anisotropy tensors of which are necessarily orthogonal to the threefold molecular axis. A similar contribution from peripheral ions is expected to rule the magnetic anisotropy in the tetra‐iron(III) complexes currently under investigation in the field of molecular spintronics.  相似文献   

10.
4,4′‐Bis(3‐N‐methoxyformyl thioureido)‐diphenyloxide was prepared via reaction of 4,4′‐diaminodiphenyl alter with potassium sulfocyanate and ethyl chloroacetate in ethyl acetate. The single crystal of the title compound was cultured by slow evaporation method at room temperature. The crystal structure was determined with X‐ray diffractometer. It is a monoclinic crystal, space group C2/c with a=0.95911(19) nm, b=0.75922(15) nm, c=2.7161(5) nm, α=90°, β=97.675 (3) °, γ=90°, V=1.9601(7) nm3, Z=4, Dc=1.472 g·cm−3, F(000) =904, µ=0.311 cm−1, R1=0.0367, wR2=0.1408. The specific heat capacity of the title compound was determined with continuous Cp mode of mircocalorimeter. The thermal behavior of the title compound was studied under a non‐isothermal condition by DSC method.  相似文献   

11.
The electrochemical, UV/Vis–NIR absorption, and emission‐spectroscopic features of (TBA+)( 1 ) and the corresponding neutral complex 1 were investigated (TBA+=tetrabutylammonium; 1 =[AuIII(Pyr,H‐edt)2]; Pyr,H‐edt2−=pyren‐1‐yl‐ethylene‐1,2‐dithiolato). The intense electrochromic NIR absorption (λmax=1432 nm; ε=13000 M −1 cm−1 in CH2Cl2) and the potential‐controlled visible emission in the range 400–500 nm, the energy of which depends on the charge of the complex, were interpreted on the grounds of time‐dependent DFT calculations carried out on the cis and trans isomers of 1 , 1 , and 1 2−. In addition, to evaluate the nonlinear optical properties of 1 x (x=0, 1), first static hyperpolarizability values βtot were calculated (βtot=78×10−30 and 212×10−30 esu for the cis isomer of 1 and 1 , respectively) and compared to those of differently substituted [Au(Ar,H‐edt)2]x gold dithiolenes [Ar=naphth‐2‐yl ( 2 ), phenyl ( 3 ); x=0, 1].  相似文献   

12.
We report the first direct spectroscopic observation by electron paramagnetic resonance (EPR) spectroscopy of a triplet diradical that is formed in a thermally induced rotation around a main‐group π bond, that is, the Si?Si double bond of tetrakis(di‐tert‐butylmethylsilyl)disilene ( 1 ). The highly twisted ground‐state geometry of singlet 1 allows access to the perpendicular triplet diradical 2 at moderate temperatures of 350–410 K. DFT‐calculated zero‐field splitting (ZFS) parameters of 2 accurately reproduce the experimentally observed half‐field transition. Experiment and theory suggest a thermal equilibrium between 1 and 2 with a very low singlet–triplet energy gap of only 7.3 kcal mol?1.  相似文献   

13.
Intersystem crossing (ISC) of triplet photosensitizers is a vital process for fundamental photochemistry and photodynamic therapy (PDT). Herein, we report the co‐existence of efficient ISC and long triplet excited lifetime in a heavy atom‐free bodipy helicene molecule. Via theoretical computation and time‐resolved EPR spectroscopy, we confirmed that the ISC of the bodipy results from its twisted molecular structure and reduced symmetry. The twisted bodipy shows intense long wavelength absorption (?=1.76×105 m ?1 cm?1 at 630 nm), satisfactory triplet quantum yield (ΦT=52 %), and long‐lived triplet state (τT=492 μs), leading to unprecedented performance as a triplet photosensitizer for PDT. Moreover, nanoparticles constructed with such helical bodipy show efficient PDT‐mediated antitumor immunity amplification with an ultra‐low dose (0.25 μg kg?1), which is several hundred times lower than that of the existing PDT reagents.  相似文献   

14.
A new energetic material, 4,5‐diacetoxyl‐2‐(dinitromethylene)‐imidazolidine (DADNI), was synthesized by the reaction of 4,5‐dihydroxyl‐2‐(dinitromethylene)‐imidazolidine (DDNI) and acetic anhydride, and characterized by single crystal X‐ray diffraction. Crystal data for DADNI are monoclinic, space group C2/c, a=15.9167(3) Å, b=8.6816(4) Å, c=8.5209(3) Å, β=103.294(9)°, V=1145.9(3) Å3, Z=4, µ=0.150 mm−1, F(000)=600, Dc=1.682 g·cm−3, R1=0.0565 and wR2=0.1649. Thermal decomposition behavior of DADNI was studied and an intensely exothermic process was observed. The kinetic equation of the decomposition reaction is: dα/dT=(1016.64/β)×4α3/4exp(−1.582×105/RT). The critical temperature of thermal explosion is 163.76°C. The specific heat capacity of DADNI was studied with micro‐DSC method and theoretical calculation method. The molar heat capacity is 343.30 J·mol−1·K−1 at 298.15 K. The adiabatic time‐to‐explosion of DADNI was calculated to be 87.7 s.  相似文献   

15.
Guanidimium‐4,4‐azo‐1‐hydro‐1,2,4‐triazol‐5‐one (GZTO·H2O) was synthesized from 4‐amino‐1,2,4‐triazol‐5‐one as a starting material by two‐step including oxidation coupling using acid KMnO4 and reaction with (NH2)2CNH·HNO3 (GN) in KOH solution. The single crystal of the title compound was obtained by slow evaporation method at room temperature, and its structure was firstly determined with X‐ray single‐crystal diffractometer. It is a orthorhombic crystal, space group Pbca with cell dimensions of a=1.0459(2) nm, b=1.3584(3) nm, c=1.6103(3) nm, α=90.00(10)°, β=90.00(11)°, γ=90.00(11)°, V=2.2878(8) nm3, Z=8, Dc=1.587 g·cm−3, F(000)=1136, µ=0.132 mm−1, R1=0.0455, wR2=0.1397. The thermal behavior of GZTO·H2O was studied under a non‐isothermal condition by DSC‐TGA method, and its thermal decomposition process can be divided into three stages, and the first stage is an intense exothermic decomposition process. The second stage and the third stage are slow exothermic decomposition processes. The critical temperature of thermal explosion is 237.74°C.  相似文献   

16.
The UV (λ>305 nm) photolysis of triazide 3 in 2‐methyl‐tetrahydrofuran glass at 7 K selectively produces triplet mononitrene 4 (g=2.003, DT=0.92 cm?1, ET=0 cm?1), quintet dinitrene 6 (g=2.003, DQ=0.204 cm?1, EQ=0.035 cm?1), and septet trinitrene 8 (g=2.003, DS=?0.0904 cm?1, ES=?0.0102 cm?1). After 45 min of irradiation, the major products are dinitrene 6 and trinitrene 8 in a ratio of ~1:2, respectively. These nitrenes are formed as mixtures of rotational isomers each of which has slightly different magnetic parameters D and E. The best agreement between the line‐shape spectral simulations and the experimental electron paramagnetic resonance (EPR) spectrum is obtained with the line‐broadening parameters Γ(EQ)=180 MHz for dinitrene 6 and Γ(ES)=330 MHz for trinitrene 8 . According to these line‐broadening parameters, the variations of the angles Θ in rotational isomers of 6 and 8 are expected to be about ±1 and ±3°, respectively. Theoretical estimations of the magnetic parameters obtained from PBE/DZ(COSMO)//UB3LYP/6‐311+G(d,p) calculations overestimate the E and D values by 1 and 8 %, respectively. Despite the large distances between the nitrene units and the extended π systems, the zero field splitting (zfs) parameters D are found to be close to those in quintet dinitrenes and septet trinitrenes, where the nitrene centers are attached to the same aryl ring. The large D values of branched septet nitrenes are due to strong negative one‐center spin–spin interactions in combination with weak positive two‐center spin–spin interactions, as predicted by theoretical considerations.  相似文献   

17.
The data on temperature, solvent, and high hydrostatic pressure influence on the rate of the ene reactions of 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione ( 1 ) with 2‐carene ( 2 ), and β‐pinene ( 4 ) have been obtained. Ene reactions 1 + 2 and 1 + 4 have high heat effects: ∆Hrn ( 1 + 2 ) −158.4, ∆Hrn( 1 + 4 ) −159.2 kJ mol−1, 25°C, 1,2‐dichloroethane. The comparison of the activation volume (∆V( 1 + 2 ) −29.9 cm3 mol−1, toluene; ∆V( 1 + 4 ) −36.0 cm3 mol−1, ethyl acetate) and reaction volume values (∆Vr‐n( 1 + 2 ) −24.0 cm3 mol−1, toluene; ∆Vr‐n( 1 + 4 ) −30.4 cm3 mol−1, ethyl acetate) reveals more compact cyclic transition states in comparison with the acyclic reaction products 3 and 5 . In the series of nine solvents, the reaction rate of 1+2 increases 260‐fold and 1+4 increases 200‐fold, respectively, but not due to the solvent polarity.  相似文献   

18.
The rate constants of the reactions of ethoxy (C2H5O), i‐propoxy (i‐C3H7O) and n‐propoxy (n‐C3H7O) radicals with O2 and NO have been measured as a function of temperature. Radicals have been generated by laser photolysis from the appropriate alkyl nitrite and have been detected by laser‐induced fluorescence. The following Arrhenius expressions have been determined: (R1) C2H5O + O2 → products k1 = (2.4 ± 0.9) × 10−14 exp(−2.7 ± 1.0 kJmol−1/RT) cm3 s−1 295K < T < 354K p = 100 Torr (R2) i‐C3H7O + O2 → products k2 = (1.6 ± 0.2) × 10−14 exp(−2.2 ± 0.2 kJmol−1/RT) cm3 s−1 288K < T < 364K p = 50–200 Torr (R3) n‐C3H7O + O2 → products k3 = (2.5 ± 0.5) × 10−14 exp(−2.0 ± 0.5 kJmol−1/RT) cm3 s−1 289K < T < 381K p = 30–100 Torr (R4) C2H5O + NO → products k4 = (2.0 ± 0.7) × 10−11 exp(0.6 ± 0.4 kJmol−1/RT) cm3 s−1 286K < T < 388K p = 30–500 Torr (R5) i‐C3H7O + NO → products k5 = (8.9 ± 0.2) × 10−12 exp(3.3 ± 0.5 kJmol−1/RT) cm3 s−1 286K < T < 389K p = 30–500 Torr (R6) n‐C3H7O + NO → products k6 = (1.2 ± 0.2) × 10−11 exp(2.9 ± 0.4 kJmol−1/RT) cm3s−1 289K < T < 380K p = 30–100 Torr All reactions have been found independent of total pressure between 30 and 500 Torr within the experimental error. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 860–866, 1999  相似文献   

19.
New rate constant determinations for the reactions CH3 + HO2 → CH3O + OH (1) CH3 + HO2 → CH4 + O2 (2) CH3 + O2 → CH2O + OH (3) were made at 1000 K by fitting species profiles from high‐pressure flow reactor experiments on moist CO oxidation perturbed with methane. These reactions are important steps in the intermediate‐temperature burnout of hydrocarbon pollutants, especially at super‐atmospheric pressure. The experiments used in the fit were selected to minimize the uncertainty in the determinations. These uncertainties were estimated using model sensitivity coefficients, derived for time‐shifted flow reactor experiments, along with literature uncertainties for the unfitted rate constants. The experimental optimization procedure significantly reduced the uncertainties in each of these rate constants over the current literature values. The new rate constants and their uncertainties were determined to be, at 1000 K: k1 = 1.48(10)13 cm3 mol−1 s−1 (UF = 2.24) k2 = 3.16(10)12 cm3 mol−1 s−1 (UF = 2.89) k3 = 2.36(10)8 cm3 mol−1 s−1 (UF = 4.23) There are no direct and few indirect measurements of reactions ( 1 ) and ( 2 ) in the literature. There are few measurements of reaction ( 3 ) near 1000 K. These results therefore represent an important refinement to radical oxidation chemistry of significance to methane and higher alkane oxidation. The model sensitivity analysis used in the experimental design was also used to characterize the mechanistic dependence of the new rate constant values. Linear sensitivities of the fitted rate constants to the unfitted rate constants were given. The sensitivity analysis was used to show that the determinations above are primarily dependent on the rate constants chosen for the reactions CH3 + CH3 + M → C2H6 + M and CH2O + HO2 → HCO + H2O2. Uncertainties in the rate constants of these two reactions are the primary contributors to the uncertainty factors given above. Further reductions in the uncertainties of these kinetics would lead to significant reductions in the uncertainties in our determinations of k1, k2, and k3. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 75–100, 2001  相似文献   

20.
The elusive triplet fluorocarbonyl nitrene, FC(O)N (X3A′′), has been generated in high yield from matrix‐isolated FC(O)N3 by ArF excimer laser photolysis (λ=193 nm). As a side product FNCO was formed. The novel nitrene was characterized by IR, UV/Vis, EPR spectroscopy, and quantum‐chemical calculations. All six fundamental vibrations of FC(O)N at 1681.3, 1193.8, 879.8, 646.5, 588.7, and 434.8 cm?1 (argon matrix, 16 K), their 12/13C, 16/18O, and 14/15N isotopic shifts, and four electronic transitions at T0=13 890, 25 428, 29 166, and 30 900 cm?1 that exhibit vibrational fine structures have been detected. Under visible‐light irradiation at λ≥495 nm, FC(O)N reacted with molecular N2 in the matrix cage at 6 K to give back FC(O)N3, whereas near‐UV irradiation at λ≥335 nm yielded FNCO. The singlet–triplet energy gaps of different carbonyl nitrenes are discussed.  相似文献   

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