Excited states transition metal complexes

Keywords TDDFT Excitation energies Excited states Transition metal complexes Electronic spectra Metallotetrapyrroles Metallocarbonyls a-diimine complexes Porphyrins Porphyrazines Phthalocyanines Werner complexes Sandwich complexes... 

Electronic transitions and excited states of metal complexes are traditionally described in terms of text-book categories such as MLCT, LLCT (XLCT), IL, MC (=LF or dd), LMCT, etc. It was mentioned several times above that MLCT, LLCT, and IL characters in the case of [Re(L)(CO)3(N,N)] represent only limiting cases. In reality, electronic transitions and excited states have mixed character owing to two factors (1) delocalization of the optical orbitals (i.e., frontier orbitals involved in electronic transitions), and (2) combining several one-electron excitations in an electronic transition. 

For the sake of simplicity, electronic transitions in metal complexes are usually classified on the basis of the predominant localization, on the metal or on the ligand(s), of the molecular orbitals involved in the transition (4). This assumption leads to the well-known classification of the electronic excited states of metal complexes into three types, namely, metal-centered (MC), ligand-centered (LC), and charge-transfer (CT). The CT excited states can be further classified as ligand-to-metal charge-transfer (LMCT) and metal-to-ligand charge-transfer (MLCT). 

Coppens, P, Fomitchev, D. V., Carducci, M. D. and Culp, K. (1998). Crystallography of molecular excited states. Transition-metal nitrosyl complexes and the smdy of transient species. J. Chem. Soc., Dalton Trans., 865-72. [30, 234]... 

The electronically excited state of a molecule is a new species with chemical properties that can differ from those of the corresponding ground state. Many of the properties of excited states can be predicted from those of ground-state species with comparable electronic configurations, especially the electron-transfer properties of excited states of metal complexes. In this section the relations between ground- and excited-state electron-transfer reactions of transition-metal complexes are discussed. 

A number of other techniques have been applied to the analysis of metal complex luminescence. Pressure effects on luminescence of coordination complexes in single crystals (either pure or doped) can also provide information of value in evaluating excited-state distortion or metal-metal interactions of ordered solid matrices." " The magnitude of transition dipole moments and polarizability can be determined using Stark spectroscopy, and Bublitz and Boxer wrote a recent review of the technique. Two-photon excitation of transition metal complex chromophores has also been observed to yield luminescence. Recent work in this area has been reviewed by Lakowitz and co-workers. ... 

A. V. Soudackov, A. L. Tchougreeff and I. A. Misurkin Ground-state multiplicities and d-d excitations of transition-metal complexes by effective Hamiltonian method, Int. J. Quantum Chem. 58, 161-173 (1996). 

INORGANIC COMPLEXES. The cis-trans isomerization of a planar square form of a rt transition metal complex (e.g., of Pt " ) is known to be photochemically allowed and themrally forbidden [94]. It was found experimentally [95] to be an inhamolecular process, namely, to proceed without any bond-breaking step. Calculations show that the ground and the excited state touch along the reaction coordinate (see Fig. 12 in [96]). Although conical intersections were not mentioned in these papers, the present model appears to apply to these systems. 

Relaxation of excited states in transition-metal complexes. M. K. DeArmond, Acc. Chem. Res., 1974,7,309-315(39). 

Busch DH (2005) First Considerations Principles, Classification, and History. 249 in press Bussiere G, Beaulac R, Belisle H, Lescop C, Luneau D, Rey P, Reber C (2004) Excited States and Optical Spectroscopy of Nitronyl Nitroxides and Their Lanthanide and Transition Metal Complexes. 241 97-118 Cadierno V, see Majoral J-P (2002) 220 53-77 Camara M, see Chhabra SR (2005) 240 279-315 Caminade A-M, see Majoral J-P (2003) 223 111-159 CantriU SJ, see Arico F (2005) 249 in press... 

The interconversion between different spin states is closely related to the intersystem crossing process in excited states of transition-metal complexes. Hence, much of the interest in the rates of spin-state transitions arises from their relevance to a better understanding of intersystem crossing phenomena. The spin-state change can alternatively be described as an intramolecular electron transfer reaction [34], Therefore, rates of spin-state transitions may be employed to assess the effect of spin multiplicity changes on electron transfer rates. These aspects have been covered in some detail elsewhere [30]. 

Balzani, V., Bolletta, F., Gandolfi, M. T., and Maestri, M. Bimolecular Electron Transfer Reactions of the Excited States of Transition Metal Complexes. 75, 1-64 (1978). 

A variety of transition metal complexes including organometallics was subjected to an ac electrolysis in a simple undivided electrochemical cell, containing only two current-carrying platinum electrodes. The compounds (A) are reduced and oxidized at the same electrode. If the excitation energy of these compounds is smaller than the potential difference of the reduced (A ) and oxidized (A ) forms, back electron transfer may regenerate the complexes in an electronically excited state (A+ + A A + A). Under favorable conditions an electrochemiluminescence (eel) is then observed (A A + hv). A weak eel appeared upon electrolysis o t]jie following complexes Ir(III)-(2-phenylpyridine-C, N ) [Cu(I)(pyridine)i],... 

The excited states which are responsible for the eel of the previous examples are of the CTML type or involved in metal-metal bonding of polynuclear complexes. Photoluminescence, or eel in our case, can also originate from intraligand (IL) excited states provided these states are the lowest excited states of such complexes. IL emissions are characteristic for many transition metal... 

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