Intra-ligand charge transfer ILCT

A ligand itself may consist of a reducing and oxidizing part [20]. The spectrum of the metal complex should then show an ILCT band which 

The donor site is the reducing thiolate moiety while the diimine is the accepting part of the chelate ligand. Such ILCT bands were also detected in the spectra of similar Zn(II) and Ni(II) complexes [72]. 

An interesting case of ILCT occurs in the complex [PtH(l-naphthylamine)2Cl2l [73]. Light absorption by the free naphthylamine leads to a shift of electron density from the nitrogen lone pair into the aromatic ring system. Ground and excited state are described by two limiting resonance structures. 

This electronic transition appears as an ILCT absorption of the platinum complex at = 293 nm. 

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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]. 

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

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...

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