Photophysics and electron transfer reactions of complexes (original) (raw)
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Inorganic Chemistry, 1997
We synthesized a new macrocycle (1) which is made of a 56-membered ring and contains two 2,9-bis(p-biphenylyl)-1,10-phenanthroline ligands. Then we prepared the complexes [Cu(1)(2)] + (a catenate species), [Cu(3) 2 ] + , [Cu(2)(3)] + (a threaded species), Re(1)(CO) 3 Cl, and Re(3)(CO) 3 Cl, where 2 is a 33-membered macrocycle containing a 2,9-di-p-phenyl-1,10-phenanthroline ligand and 3 is an acyclic ligand containing the same 2,9-bis-(p-biphenylyl)-1,10-phenanthroline unit which is present in 1. The absorption spectra of the free ligands in CH 2 -Cl 2 solution show very intense bands in the near-UV region, characteristic of their aromatic moieties. In the Cu(I) complexes, besides the perturbed ligand-centered bands, weak metal-to-ligand charge-transfer (MLCT) bands can be observed in the 400-700 nm region. In the Re(I) complexes the MLCT bands lie at higher energy because the oxidation potential of Re(I) is much more positive than that of Cu(I). At room temperature, ligands 1 and 3, which contain an extensively conjugated aromatic unit, show a very strong (Φ ) 0.89), short-lived (1.7 ns) fluorescence band with λ max ) 419 nm. The fluorescence of 2 is blue shifted (λ max ) 387 nm) and less intense (Φ ) 0.29) because of the less extended conjugation and rigidity of its chromophoric unit. Besides fluorescence, also a long-lived (second time scale) phosphorescence is displayed by the three ligands in a rigid matrix at 77 K. At room temperature the [Cu(1)(2)] + , [Cu(3) 2 ] + , and [Cu(2)(3)] + species exhibit a weak (Φ ∼ 10 -3 ), relatively long-lived (10 2 ns time scale) emission with λ max around 750 nm, which can be assigned to a triplet metal-toligand charge-transfer ( 3 MLCT) excited state. This emission is slightly red shifted and considerably longer lived (τ ∼ 2 µs) at 77 K. The Re(1)(CO) 3 Cl and Re(3)(CO) 3 Cl complexes at room temperature show a moderately weak (Φ ∼ 10 -2 ), long-lived (10 2 ns time scale) 3 MLCT emission with λ max around 610 nm. At 77 K this emission is blue shifted (λ max ) 560 nm) and considerably longer lived (τ ∼ 10 µs). In the [Cu(1)(2)] + catenate and in the Re(1)(CO) 3 Cl complex one of the two chelating sites of the macrocycle 1 is coordinated to the metal and the other one is free. Besides a 3 MLCT emission, these species exhibit the fluorescence band of the 2,9bis(p-biphenylyl)-1,10-phenanthroline unit, strongly quenched by the nearby metal-based chromophoric unit (k q ) 1.6 × 10 10 and 1.4 × 10 10 s -1 for the Cu(I) and the Re(I) complex, respectively). In aerated solution all of the complexes sensitize the 1 ∆ g (O 2 ) luminescence at 1269 nm. De Cola, L.; Balzani, V.; Sauvage, J.-P.; Dietrich-Buchecker, C. O.; Kern, J.-M. J. Chem. Soc., Faraday Trans. 1992, 88, 553. (b) Armaroli, N.; De Cola, L.; Balzani, V.; Sauvage, J.-P.; Dietrich-Buchecker, C. O.; Kern, J.-M.; Bailal, A.
Inorganic Chemistry, 2004
Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the Re(I) halide bipyridine complex ReCl(CO) 3 (bpy) (1) and the related complexes ReCl(CO) 3 (5,5′-dibromo-bpy) (2), ReCl-(CO) 3 (4,4′-dimethyl-bpy) (3), and ReCl(CO) 3 (4,4′-dimethylformyl-bpy) (4) (where bpy ) 2,2′bipyridine). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using the B3LYP functional. Excited singlet and triplet states are examined using time-dependent DFT (TDDFT). The low-lying excited-state geometries are optimized at the ab initio configuration interaction singlets (CIS) level. As shown, the occupied orbitals involved in the transitions have a significant mixture of the metal Re and the group Cl, by the amount of metal 5d character which varies from 30 to 65%. The lowest unoccupied molecular orbital (LUMO) is a π* orbital of the ligand bpy for the series of molecules. The TDDFT result indicates that the absorption maxima are at relatively high energy and are mainly assigned to bpy-based ππ* transitions with somewhat metal-to-ligand charge transfer (MLCT) [d(Re) f π*(bpy)] and ligand-to-ligand charge transfer (LLCT) [p(Cl) f π*(bpy)] except for complex 3, in which this band is mainly assigned to mixed MLCT/LLCT, and overlaps bpy ππ* character. All the low-lying transitions are categorized as mixed MLCT/LLCT. The absorption bands are blue shifted when substituted by an electron-releasing group (-CH 3 ), and they are red shifted when substituted by an electron-withdrawing group (-Br or -COOCH 3 ). The luminescence of all complexes is assigned as a triplet metal/chlorine to bpy charge transfer (MLCT/LLCT).
0riginal article, 2020
To cite this article: Dereje Fedasa, Dunkana Negussa, Alemu Talema. Effect of Substituents on Electronic Structure and Photophysical Properties of Re(I)(CO) 3 Cl(R-2, 2'-Bipyridine) Complex: DFT/TDDFT Study. Abstract: The electronic structure, absorption and emission spectra, as well as phosphorescence efficiency of Re(I) tricarbonyl complexes of a general formula fac-[Re(I)(CO) 3 (L)(R-N^N)](L = Cl; N^N = 2, 2'-bipyridine; R =-H, 1;-NO 2 , 2;-PhNO 2 , 3;-NH 2 , 4;-TPA (triphenylamine), 5) were investigated by using density functional theory(DFT) and time dependents density functional theory (TDDFT) methods. The calculated results reveal that introductions of the Electron with drawing group (EWG) and Electron donating group (EDG) on the R position of 2, 2'-bipyridine ligand. When EWG (-NO 2 and-PhNO 2) are introduced into complex 2 and 3, the lowest energy absorption and emission bands are red shifted compared with that of complex 1. On the contrary, the introduction of the EDG (-NH 2 and-TPA) in complex 4 and 5 cause corresponding blue shifted. The solvent effect on absorption and emission spectrum indicates that the lowest energy absorption and emission bands have red shifts with the decrease of solvent polarity. The electronic affinity (EA), ionization potential (IP) and reorganization energy (λ) results show that complex 5 is suitable to be used as an emitter in phosphorescence organic light emitting diodes (PHOLEDs). Meanwhile the emission quantum yield of complex 5 is possibly higher than that of other complexes.
Journal of Physical Chemistry A, 2004
Density functional theory (DFT) is applied to analyze ground-and excited-state properties of the Re(I) halide bipyridine complex ReCl(CO) 3 (bpy) (1) and the related complexes ReCl(CO) 3 (5,5′-dibromo-bpy) (2), ReCl-(CO) 3 (4,4′-dimethyl-bpy) (3), and ReCl(CO) 3 (4,4′-dimethylformyl-bpy) (4) (where bpy ) 2,2′bipyridine). The electronic properties of the neutral molecules, in addition to the positive and negative ions, are studied using the B3LYP functional. Excited singlet and triplet states are examined using time-dependent DFT (TDDFT). The low-lying excited-state geometries are optimized at the ab initio configuration interaction singlets (CIS) level. As shown, the occupied orbitals involved in the transitions have a significant mixture of the metal Re and the group Cl, by the amount of metal 5d character which varies from 30 to 65%. The lowest unoccupied molecular orbital (LUMO) is a π* orbital of the ligand bpy for the series of molecules. The TDDFT result indicates that the absorption maxima are at relatively high energy and are mainly assigned to bpy-based ππ* transitions with somewhat metal-to-ligand charge transfer (MLCT) [d(Re) f π*(bpy)] and ligand-to-ligand charge transfer (LLCT) [p(Cl) f π*(bpy)] except for complex 3, in which this band is mainly assigned to mixed MLCT/LLCT, and overlaps bpy ππ* character. All the low-lying transitions are categorized as mixed MLCT/LLCT. The absorption bands are blue shifted when substituted by an electron-releasing group (-CH 3 ), and they are red shifted when substituted by an electron-withdrawing group (-Br or -COOCH 3 ). The luminescence of all complexes is assigned as a triplet metal/chlorine to bpy charge transfer (MLCT/LLCT).
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2005
h i g h l i g h t s Spectroscopic investigations on the interaction of 2-hydroxypyridine as an electron donor with rand p-acceptors. rand p-acceptors used in this study are iodine, chloranilic acid and 2,3-dichloro-5,6-dicyano-p-benzoquinone. The prepared CT-complexes have the general formula [(HPyO)(acceptor)]. Formation constant, charge transfer energy and thermal analyses data of CT-complexes are presented.
Inorganica Chimica Acta, 1996
We have synthesized a number of dinuclear species containing both identical or different metal-based components by employing new bridging ligands having either atiphatic or aromatic spacers and taking advantage of the "'complexes as metals and complexes as ligands'" synthetic strategy. The bridging ligands are dpt-S-dpt (S is 1,4-cyclohexyt, 1,4-phenyl, 4,4'-biphenyl; dpt is 4-amino-3,5-bis(2-pyridyl)-1,2,4-triazole; the connections between S and dpt are provided by amide links). The complexes synthesized are: [(bpy):Ru(dpt-Sdpt)Ru(bpy).~](PF6)4 (bpy-2,2'-bipyridine; biq=2,2'-biquinoline; S=l,4-cyclohexyl (1), 1,4.-phenyl (4), 4,4'-biphenyl (7)); [(biq)2Ru(dpt-S-dpt)Ru(biq)2](PF6)4 (S=l,4-cyclohexyl (2), i,4-phenyl (5), 4,4'-biphenyl (8)); [(bpy._Ru(dpt-S-dpt)-Ru(biq)-, ] (PF6)4 (S = 1,4-cyclohexyl (3), 1,4-phenyl (6), 4,4'-biphenyl (9)). The absorption spectra, luminescence properties and redox behavior of all the compounds have been studied, in the complexes containing different metal-based components, photoinduced energy transfer occurs from the higher-lying Ru-~ bpy CT level, centered on a metal subunit, to the lower-lying Ru ~ biq CT excited state, centered on the other metal component. In fluid solution at room temperature, the energy transfer is suggested to be mediated by a two-step electron transfer mechanism, whereas direct energy transfer between the chromophores most likely occurs at 77 K in rigid matrix. At the momenl we are not able to say if the energy transfer at 77 K takes place via electron exchange or coulombic mechanisms. The results obtained indicate that the efficiency of the processes depends on the donor-aeceptor distance, as expected, and that occasional rr bonds which are present within the bridging ligands cannot be used for speeding up electron transfer in multicomponent systems if the main skeleton of the bridge is made by o" bonds.
International journal of computational and theoretical chemistry, 2020
The electronic structure, absorption and emission spectra, as well as phosphorescence efficiency of Re(I) tricarbonyl complexes of a general formula fac-[Re(I)(CO) 3 (L)(R-N^N)](L = Cl; N^N = 2, 2'-bipyridine; R =-H, 1;-NO 2 , 2;-PhNO 2 , 3;-NH 2 , 4;-TPA (triphenylamine), 5) were investigated by using density functional theory(DFT) and time dependents density functional theory (TDDFT) methods. The calculated results reveal that introductions of the Electron with drawing group (EWG) and Electron donating group (EDG) on the R position of 2, 2'-bipyridine ligand. When EWG (-NO 2 and-PhNO 2) are introduced into complex 2 and 3, the lowest energy absorption and emission bands are red shifted compared with that of complex 1. On the contrary, the introduction of the EDG (-NH 2 and-TPA) in complex 4 and 5 cause corresponding blue shifted. The solvent effect on absorption and emission spectrum indicates that the lowest energy absorption and emission bands have red shifts with the decrease of solvent polarity. The electronic affinity (EA), ionization potential (IP) and reorganization energy (λ) results show that complex 5 is suitable to be used as an emitter in phosphorescence organic light emitting diodes (PHOLEDs). Meanwhile the emission quantum yield of complex 5 is possibly higher than that of other complexes.
Optics and Spectroscopy, 2010
Cyclometalated [M(C^N)(µ (N-S))] 2 complexes ((M = Pd(II), Pt(II)), (C^N)are the depro tonated forms of 2 tolylpyridine and benzo[h]quinoline, and (N⎯S)are pyridine 2 thiolate and benzothi azole 2 thiolate ions) are studied by 1 H NMR, IR, electronic absorption, and emission spectroscopy, as well as by voltammetry. It is shown that the formation of the metal-metal chemical bond and the orbital as a HOMO of complexes leads to the long wavelength spin allowed (410-512 nm) and spin forbidden (595-673 nm) optical transitions in the absorption and phosphorescence spectra, as well as to the two electron and successive one electron oxidation with the formation of binuclear Pt(III) and Pd(III) com plexes. The substitution of Pt(II) by Pd(II) is characterized by hypso and bathochromic shifts of the spin allowed and forbidden optical transitions in the absorption and phosphorescence spectra of com plexes, by phosphorescence quenching of Pd(II) complexes in liquid solutions, and by an anodic shift of the oxidation potential of Pd(II) complexes compared with Pt(II) complexes.
Inorganic Chemistry, 1989
A series of dirhenium complexes of the type Re2(CO),(p-H)(p-py)(L), where L = CO or py and py = pyridine or 4-benzoylpyridine, have been synthesized. Excited-state properties of these and related rhenium carbonyl complexes containing pyridine or 4benzoylpyridine as a-bound or p-bridged ligands have been investigated in an effort to design organometallic complexes that possess long-lived excited states generated from the photoexcitation of the M-M a-bond. Emissive metal-to-ligand charge-transfer states of the type dl(M)r*L or UM-MT*L have been observed in complexes containing bridging ligands, and their intermolecular electron-transfer reactions with a variety of neutral or charged donors and acceptors have been studied by emission and transient absorption spectroscopic techniques. Quenching of [Re2(C0)7(p-H)(p-py)(L)] * (py = L = 4-benzoylpyridine) by a series of trialkyl-and triarylphosphines is shown to proceed solely by electron-transfer pathways. We have also studied the electron-transfer reduction of a series of substituted N-methylpyridinium salts by the same excited-state molecule and attempted to correlate the rate of electron tranfser with the reduction potential of the quencher.