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Loukova, G. V.; Smirnov, V. N.

doi:10.1023/a:1009515409620

Cited by 21 publications

(40 citation statements)

References 4 publications

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“…At the same time, some luminescence characteristics of these complexes 8, 16 (for instance, the lifetimes at 77 K are 2 ms (Zr) and ∼0.3 ms (Hf)) and the catalytic 9,10 and redox 13,14 proper ties differ appreciably due to the strong spin orbital inter action for Hf compared to that for Zr (see Ref. 20).…”

Section: Resultsmentioning

confidence: 98%

“…Quenching of luminescence of the zirconium and hafnium π complexes was found in glassy solutions, which seems to be due to chemical inter actions. (The absorption spectra of the metallocenes have very broad structureless bands 8, 16 and are much less infor mative than the luminescence characteristics.) The inter action of the metallocenes with unsaturated triplet accep tors revealed unexpected features: none of the UHCs, except for cyclopentadienes, quenches Cp 2 ZrCl 2 lumi nescence.…”

Section: Resultsmentioning

confidence: 99%

“…[1][2][3][4][5][6] No systematic studies of excited states formed due to the ligand to metal charge transfer (LMCT) are known. [4][5][6][7][8] Metallocene complexes play an important role in the catalytic production of polyethylene and polypropylene and activation of small inert molecules (N 2 , CO, CO 2 , and others). Based on bent metallocenes of Group IVB elements, viz., 16 electron complexes of d 0 metal ions with polyhapto and monodentate ligands (π L) 2 M IV X 2 (X is halogen, alkyl, etc.…”

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Effect of the coordination sphere of d0 metallocene on triplet-triplet energy transfer

2007

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The triplet nature of rare long lived states of d 0 metallocenes formed upon ligand to metal energy transfer was confirmed by studies of triplet triplet charge transfer in biscyclopentadienyl complexes Cp 2 MCl 2 (М = Zr (1), Hf (2)). The interaction between precatalysts and substrates of catalytic polymerization systems, viz., complexes 1 and 2 and unsaturated hydrocarbons (alkenes and dienes), was studied in the region of concentrations close to catalytic values. For organometallic π complexes, it has been shown for the first time that, in the case of the unsaturated hydrocarbons, the efficiency of energy transfer obeys the Perrin equation. The process occurs at distances R 0 close to the diameter of the interacting molecules and is well described by the exchange resonant mechanism of interaction. In the case of the cyclo pentadiene-Cp 2 MCl 2 (М = Zr, Hf) systems, R 0 = 14.6 Å. A linear relationship between the critical radius of the quenching sphere R 0 and the number of carbon atoms in a linear α olefin has been revealed for the first time and evidences the formation of a π complex between the precatalyst and substrate molecules.Key words: energy transfer, triplet triplet quenching of luminescence, excited states of organometallic compounds, ligand to metal charge transfer, phosphorescence, zirconinum complexes, hafnium complexes.Traditionally, investigations on photochemistry of co ordination and organometallic compounds were focused on search for long lived excited states and their use in solar energy storage and conversion, data recording and processing, and photocatalysis. 1-6 The presence of tran sition metal ions in coordination molecules causes partial or complete removal of the spin forbidden nature due to a strong spin orbital interaction and also results in nonradiative energy degradation due to vibrational cou pling because of high convalence of metal-ligand bonds. In contrast to various phosphorescent states based on or ganic molecules, long lived radiative states based on co ordination (especially organometallic) compounds are vir tually unknown; the properties of compounds of late tran sition metals are mainly studied. 1-6 No systematic studies of excited states formed due to the ligand to metal charge transfer (LMCT) are known. 4-8Metallocene complexes play an important role in the catalytic production of polyethylene and polypropylene and activation of small inert molecules (N 2 , CO, CO 2 , and others). Based on bent metallocenes of Group IVB elements, viz., 16 electron complexes of d 0 metal ions with polyhapto and monodentate ligands (π L) 2 M IV X 2 (X is halogen, alkyl, etc.), a large number of practically valuable systems were proposed (e.g, catalysts for olefin polymerization 9-12 ).For the metallocene triad Cp 2 M IV X 2 (M = Ti, Zr, Hf) we developed an experimental approach to essessment of the properties and estimation of the relative energies of the frontier MOs (HOMO, LUMO) of organometallic π complexes 8,13-16 and started systematic investigations of rare radiative LMCT states of...

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Section: Resultsmentioning

confidence: 98%

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

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Effect of the coordination sphere of d0 metallocene on triplet-triplet energy transfer

2007

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“…The long lived excited state of complex 1 is formed due to the ligand to metal charge transfer, which is rarely observed in the photophysics of organometallic compounds. [10][11][12] Solutions of single crystals were studied. All solvents used were multiply purified from traces of impurities, oxy gen, and moisture and subjected to freezing-thawing out cycles using known procedures.…”

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Intense luminescence of the group IVB metal π-complex in solutions at room temperature

2007

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Studies of luminescence, in particular, phosphore scence, are significant in development of the theory of triplet state. 1-3 An important role in photophysics and photochemistry belongs to the solvent, which can also be a reactant and specific quencher of luminescence: the majority of molecules do not luminesce in the liquid phase. Compounds of Group IVB metals 4,5 gained special sig nificance as catalysts of many organic reactions, includ ing olefin polymerization 6-8 and activation of small inert molecules (N 2 , CO, CO 2 , etc.). 9 However, no systematic studies on the interaction of organometallic complexes of early transition metals (in particular, Group IVB metals) with the medium were carried out.The previous study of the Cp 2 M IV Cl 2 complexes (Cp = η 5 C 5 H 5 , M = Ti, Zr, Hf) has revealed 10 their lumines cence in solid solutions at low temperature and in poly crystals at low and elevated temperatures. In the present work, we studied for the first time the d 0 metallocene complex based on the Group IVB metal, namely, racemate of trans 1,2 [(bis(η 5 tetrahydroindenyl)cyclohexane]zir conium(IV) dichloride, rac C 6 H 10 (IndH 4 ) 2 ZrCl 2 (1), which intensely luminesces in liquid solutions. The long lived excited state of complex 1 is formed due to the ligand to metal charge transfer, which is rarely observed in the photophysics of organometallic compounds. 10-12Solutions of single crystals were studied. All solvents used were multiply purified from traces of impurities, oxy gen, and moisture and subjected to freezing-thawing out cycles using known procedures. 10-12 The concentration of the complex in solutions was 10 -5 -10 -4 mol L -1 . Spec tral measurements were conducted by an earlier described procedure. 13 Complex 1 luminesces in the liquid phase at room temperature (the luminescence lifetime in hydrocarbon media is ∼2 ms at 77 K). The absorption and lumine scence spectra of complex 1 at 20 °C in acetonitrile and methylcyclohexane are shown in Fig. 1. It can be seen that an increase in the polarity of the solvent results in the red shift of the absorption spectra and (to a greater extent) luminescence spectra: up to 1000 cm -1 and more. The quantum yields (Φ) of luminescence of solutions pre sented in Fig. 2 (to Φ ∼30% in dichloromethane) are Fig.

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“…All solvents were subjected to spe cial repetitive purification from traces of admixtures, oxy gen, and moisture using freezing-thawing out cycles in a high vacuum line according to known procedures. [1][2][3][4] The concentration of the complex in solutions was 3•10 -5 -2•10 -4 mol L -1 . The lifetimes were determined upon the excitation of solutions of metallocene 1 by a photodiode laser with λ exc = 375 nm on a Fluotime 200 fluorimeter (PicoQuant GmbH, Germany) using the pho ton counting method and the commercial FluoFit pro gram package.…”

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Simple correlation between the main luminescence parameters of the metallocene complex in the liquid phase

2007

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Metallocene complexes of Group 4B metals possess rather uncommon phosphorescent states 1-5 appearing due to the ligand to metal charge transfer (LMCT). 1-12 The luminescence quantum yields (Φ L ) and lifetimes of elec tronically excited states (τ) of metallocenes of the tita nium subgroup are among highest and longest ones for the known LMCT states and other radiative states (T→S 0 ) of coordination compounds. In the present work, we stud ied the lifetimes of the LMCT excited states of metallocene rac C 6 H 10 (IndH 4 ) 2 ZrCl 2 (1) 13 (Ind is indenyl) in solu tions. This metallocene intensely luminesces in the liquid state at room temperature. The proportional dependence Φ L ∝ τ of the radiative characteristics of compound 1 was observed in solvents of different solvating ability.Solutions prepared from single crystals of com pound 1 were studied. All solvents were subjected to spe cial repetitive purification from traces of admixtures, oxy gen, and moisture using freezing-thawing out cycles in a high vacuum line according to known procedures. 1-4 The concentration of the complex in solutions was 3•10 -5 -2•10 -4 mol L -1 . The lifetimes were determined upon the excitation of solutions of metallocene 1 by a photodiode laser with λ exc = 375 nm on a Fluotime 200 fluorimeter (PicoQuant GmbH, Germany) using the pho ton counting method and the commercial FluoFit pro gram package. The luminescence quantum yields of solu tions of compound 1 were determined by a comparison of the integral luminescence intensities of the sample (D x ) and standard solution (D st ) with a correction for the dif ference of the refractive coefficients of the solvent in the sample (n x ) and in the standard (n st ) using the known formula Φ L,x /Φ L,st = (n x 2 /n st 2 )(D x /D st ).An anthracene solution in ethanol (Φ L,st = 0.27) was used as standard. 14 The accuracy of determination of Φ L was at least ±10%.We obtained a linear correlation for the main emission parameterswhere k r is the radiative deactivation constant for the excited state (for solutions of 1 k r = 2.36•10 4 s -1 ; Fig. 1), which was observed for the first time for the luminescence of all known molecules in solutions. The solvent deter mines the nonradiative deactivation rate (k nr ) rather than k r , which is expressed as the relation Φ L ∝ τ. Note that the Φ L and τ parameters strongly depend nonlinearly on the medium effects, most probably, because of specific

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Cited by 21 publications

References 4 publications

Effect of the coordination sphere of d0 metallocene on triplet-triplet energy transfer

Effect of the coordination sphere of d0 metallocene on triplet-triplet energy transfer

Intense luminescence of the group IVB metal π-complex in solutions at room temperature

Simple correlation between the main luminescence parameters of the metallocene complex in the liquid phase

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