Correlation between the Luminescence Behavior of Octahedral Chromium(III) Complexes and the Ligand-Field Strength

Abstract

An empirical rule for the type of luminescence (fluorescence only, fluorescence and phosphorescence, phosphorescence only) to be expected, which depends on the position of the respective ligands in the spectrochemical series, has been found for octahedral chromium (III) complexes. This correlation is discussed in terms of the shape and intersection of potential-energy surfaces.

Metal centered ligand field excited states: Their roles in the design and performance of transition metal based photochemical molecular devices

“…This same relationship between spectral width and distortion applies to the emission spectra ( Fig. 8) [47]. Cr(III) complexes of O h symmetry typically show two broad spin allowed "quartet" absorption bands for 4 A 2g → 4 T 1g and 4 A 2g → 4 T 2g (e.g., see Fig.…”

“…NH 3 , CN − ). Dual emission (i.e., P accompanied by F) is sometimes observed for the intermediate case of oxygen donors [47]. A classic example is the dual emission observed for the complex Cr(urea) 6 3+ in a 78 K glass [48].…”

“…From the thermally equilibrated doublets, there is the possibility of (i) BISC, (ii) phosphorescence, or (iii) NR (another Adapted from Ref. [47].…”

Excited States of Metal Complexes and their Reactions

“…Two semiempirical procedures have been reported for predicting the type of emission of a chromium complex from measurable quantities of the absorption spectrum (42,46,60). Both of these methods have made use of 4L1 energies, but both have had failures even among complexes with nominally octahedral ground state symmetry.…”

“…Both of these methods have made use of 4L1 energies, but both have had failures even among complexes with nominally octahedral ground state symmetry. For example, in the earlier proposal (42,46) the energy difference AE = E(4L1) -E('D) was used to predict phosphorescence, fluorescence, or both types of emission, but complexes 4, 5, and 6 in Table I1 are exceptions to the rule (55). Furthermore, when the results of solution-and solid-phase studies of these and other complexes (43,61,62) are compared, peculiar behavior, not consistent with the AE relationship, is observed.…”