Intraligand charge transfer complexes

These complexes display an intense absorption at 400-550 nm due to intraligand charge-transfer absorption, which allows visible-light excitation of NIR-emitting Nd(III), Er(III), and Yb(III) ions with excitation wavelengths up to 550 nm. 

Yersin, H. Donges, D. Nagle, J. K. Sitters, R. Glasbeek, M. Intraligand charge transfer in the Pd(II) oxinate complex Pd(qol)(2). Site-selective emission, excitation, and optically detected magnetic resonance. Inorg. Chem. 2000, 39, 770-777. 

Several reports have taken advantage of this unique property to design a variety of photoswitching systems in recent years.Moore and co-workers reported one particularly interesting example. The complexes in their study are yhc-Re(CO)3(bpy) chromophores linked by a styryl pyridine that attaches an amine or an azacrown ether group (see Scheme 4 for structures). The absorption spectra of these complexes feature an intense intraligand charge-transfer (ILCT) band, which can be removed by protonation of the amine or azacrown... 

The complex Pd2(dba)3 in solution shows electronic absorption bands at 350, 380, and 545 nm. The band at 350 nm is due to an intraligand charge transfer transition. The band at 380 nm is due to an intermetallic da pa transition, and the lowest energy band at 545 nm is due to an MLCT transition. " The triplet emission from this complex is observed at 730 nm. By comparison, the absorption bands for Pt2(dba)3 are found at 350,400, and 620 nm, respectively, and the triplet emission is observed at 800 nm. An analysis of the ground state spectroscopic parameters reveals that both the palladium and the platinum complexes have only weak intermetallic interactions. For Pd2(dba>3 the intermetallic stretching frequency V (M-M) is found at 76 cm , which corresponds to a force constant of 0.18 mdyn A By comparison the corresponding stretching frequency in Pt2(dba)3 is found at 72 cm" which corresponds to a force constant of 0.30 mdyn A" when the mass difference is taken into consideration. ... 

It is briefly mentioned that the situation for Pt(II) complexes with qol" and qtl" ligands is different, since in these compounds the lowest excited states result from intraligand-charge transfer transitions ( ILCT) with very small metal admixtures [195,315,318,319]. This class of compounds exhibits highly efficient red to infrared emissions. It is noted that these Pt(II) compounds are related to systems like Al(qol)3 [315,318,319], which are of great interest for light-emitting electroluminescent devices for flat panel display systems [320,321]. 

The complex shown in Figure 3.9 [104] is luminescent in the solid state at 77 K with three emission maxima at 431,448 and 460 nm. The excitation maxima are at 305 and 370 nm. The origin of the luminescence has been attributed to intraligand transitions with contributions of charge transfer character. 

Figure 4.75 Schematic representation of the charge transfer in various excited states of a metal complex. M is the metal centre and L stands for a ligand. LF is a ligand field transition, CTs are the charge transfer transitions, LL is an intraligand transition, and CTTS is a charge transfer to solvent...

TDDFT calculations results were consistent with the band shapes of the optical spectra of the parent complexes and are shown in Fig. 14. The calculated optical transitions are shown as bars under the experimental spectra and consist of MLLCT, ligand-to-ligand charge transfer transitions (LLCT), intraligand n - tt transitions (IL), and metal-complex delocalized-charge transfer transitions (MCDCT). Triplet state energies were also calculated based on a3 MLLCT state and correlated with experimental emission spectral results [53]. 

Figure 6.17(a) shows the time-resolved transient absorption spectra obtained for [Ru(dcbpy)2(bpzt)] in aqueous solution at pH 7. The important features are the bleaching of an absorption feature with a maximum at 450 nm and the growing in of a new band at 350 nm. The bleaching process can be attributed to the disappearance of the metal-to-ligand charge-transfer (MLCT) transitions in the excited state, while the feature at 350 nm is indicative of intraligand transitions of the dcbpy radical formed upon excitation of the complex. This type of behavior which is typical... 

The Ru(phen)2(dppz)2+-chromophore is the electron donor in this study. It has absorbance maxima in aqueous solution at 372 and 439 nm, respectively, e = 2.48 and 2.23 x 104 M 1 cm-1. The absorbance at 439 nm arises from a metal to ligand charge transfer (MLCT) transition that is common to tris(bipyridyl)-ruthenium(II) complexes, while the absorbance at 372 arises from an intraligand... 

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