Intra-ligand charge transfer states

Shavaleev, N.M., Scopelliti, R., Gumy, R, andBunzli, J.C.G. (2008) Visible-light excitation of infrared lanthanide luminescence via intra-ligand charge-transfer state in 1,3-diketonates containing push-pull chromophores. European Journal of Inorganic Chemistry, (9), 1523-1529. 

Del Guerzo, A. Leroy, S. Fages, F. Schmehl, R. H. Photophysics of Re(I) and Ru(II) diimine complexes covalently linked to pyrene contributions from intra-ligand charge transfer states. Inorg. Chem. 2002, 41, 359-366. 

Fig. 7 Schematic representation of energy absorption, migration, emission (plain arrows) and dissipation (dotted arrows) processes in a lanthanide complex. S or S = singlet state, T or T = triplet state, A = absorption, F = fluorescence, P = phosphorescence, k = rate constant, r = radiative, nr = nonradiative, IC = internal conversion, ISC = intersystem crossing, ILCT (or IL) = intra-ligand charge transfer, LMCT (or LM) = ligand-to-metal charge transfer. Back transfer processes are not drawn for the sake of clarity...

An alternative route to long-lived excited states in transition metal complexes is to populate an excited state localised on a pendant arm. For example, a switch from a very short lived MLCT state in [Pt(tpy)Cl] to a long-lived intra-pyrene excited state in [(4 -pyrene)-tpy-Pt-Cl] , has been demonstrated an electron-rich aryl substituent at the 4 position of the tpy ligand promotes the low-lying excited state with intra-ligand charge-transfer (ILCT) character, enhances the emission intensity, and extends the excited-state lifetime up to 64 ps in r.t. dichloromethane solution [35]. 

Here, the dipole operator r is divided into two contributions r(A/) and r(L) which operate only within the Mg and Eg states, respectively, excluding the possibility of charge transfer effect. Focusing on the matrix elements of dipole operators in Eq. (6), the first and second terms, which contain (Ma r(M) Mc ) and Mg r M) Mb), express intrametal excitations derived from the JO theory and the third and fourth terms, which contain (Lg r(L) Le ) and (Le r(L) Lg), express intra-ligand excitations derived from the DC model. When the Coulombic potential between nonoverlapping transition charge distributions of Mb and... 

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