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  • Author: Amd Vogler x
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Abstract

[Re(riboflavin)(CO)3Cl] shows intraligand (λmax = 476 and 518 nm) and Re(I) to π* (riboflavin) metal-to-ligand charge transfer, MLCT, (λmax = 556 nm, in CH3CN) absorptions in close proximity. The MLCT band undergoes a moderate solvent-dependent shift (negative solvatochromism) indicating a partial charge separation in the excited state. The complex is not photoluminescent.

Abstract

The complex of ReCl(CO)3(PhNH-NH2)2 shows an absorption band at λmax = 272 nm which is assigned to an IL (intraligand) transition of the coordinated phenylhydrazine. Upon IL excitation the complex undergoes a decomposition with ϕ = 0.03 at λirr = 280 nm.

Peroxoborate and the oxidizing cations [Co(NH3)6]3+, [Ru(NH3)6]3+ and N,N′-dimethyl-4,4′- bipyridinium2+ (paraquat2+) form ion pairs in aqueous solutions which display outer-sphere charge transfer (OSCT) bands in their absorption spectra. This CT involves an electronic transition from the peroxo substituents of peroxoborate to the cations. When 10,10′-dimethyl- 9,9′-biacridinium2+ (lucigenin2+, LG2+) is used as an electron acceptor an OSCT absorption is not observed owing to the instability of the ion pair LG2+ peroxoborate which undergoes a chemiluminescent conversion to N-methylacridone.

Re(1,2-diimine)(CO)3Cl complexes with the aliphatic bidentate ligands diiminosuccinodinitrile (DISN), benzilbisanile (BEAN), bisacetylbisanile (BABA), and benzildiimine (BEDIM) are reported. The compounds show Re(I) to π*(diimine) metal-to-ligand charge transfer (MLCT) absorptions in the visible spectral region. The energy of these MLCT-transitions decreases in the series BABA > BEDIM > BEAN > DISN, depending on the π* acceptor properties of the coordinated diimine ligands. The maxima of these CT bands undergo a solvent-dependent shift (negative solvatochromism), which indicates a partial charge redistribution in the excited state. The compounds are not photoluminescent at room temperature and 77 K.

1,3-Dimethyluracil (DMU) forms a complex with copper(I) iodide which shows a green luminescence at λmax = 505 nm. With PF6 - counter ions a photoactive Cu(I)DMU complex is generated which shows a long-wavelength absorption at λmax = 335 nm. Light absorption by this band leads to a dimerization of DMU to its cyclobutane dimer.

The complexes Re(L-L)(CO)3Cl with L-L = 9,10-phenanthrenequinone (PHQ) and 9,10- phenanthrenequinone diimine (PHI) were prepared and characterized spectroscopically. Both compounds show intense Re(I) to L-L metal-to-ligand charge transfer (MLCT) absorptions. In chloroform, the MLCT bands appear at 711 nm (L-L = PHQ) and 553 nm (L-L = PHI).