Intraligand-charge transfer absorption

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. 

It is also possible that coordination of a metal alters the electron affinity of a portion of the ligand, resulting in observation of absorption and emission from a eharge transfer state localized on the ligand (intraligand charge transfer, ILCT). ... 

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. ... 

Electronic absorption spectroscopy charge transfer transitions, 19 71 d-d transitions, 19 70, 71 flavocytochrome b, 36 269-271 intraligand transitions, 19 71-80 of organometallics, 19 69-80 Electronic coupling, between donor and acceptor wave functions, 41 278 Electronic nuclear double resonance spectroscopy, molybdenum center probes, 40 13... 

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... 

FIGURE 1 A schematic absorption spectrum of a transition metal complex ion in the UV-VIS region. The central ion bands correspond to d d transitions the ligand bands correspond to charge transfer transitions and/or to intraligand transitions. 

Optical properties. The energetic differences between the ground state and the few lowest excited states, mainly d-d transition, correspond to the absorption bands in the spectral region with X > 300-700 nm, with extinction coefficient of 10 -10. There are also bands with much higher extinction coefficient (10 -10 ) which normally correspond to charge transfer band or intraligand transition. These bands are responsible for the color of the compound (Section III). 

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