Intra-ligand charge-transfer

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. 

LC ligand centered MLCT metal-to-ligand charge transfer ILCT intra-ligand charge transfer. 

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]. 

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