Ligand field phosphorescence

Many other rhodium(III) complexes exhibit ligand field phosphorescence, including a number of amine complexes (186-188) RhCl/L (L = phen and substituted phen) (189) Rh(dtp) and Rh(dmtc)3 (190) Rh(dppe)2Cl2 and Rh(dpae)2Cl2 (191) and Rh(py)2Cl4 (163). 

II Ligand field effects (from unpaired electrons in transition metal ions and complexes) Phosphorescence, lasers... 

Luminescence spectrocopy is potentially a powerful technique for studying chromium(III) complexes and a series of fluoro and aqua complexes have been studied.1066 The luminescence correlates well with ligand field strength and, at. liquid air temperatures, the lifetime of the doublet state from which phosphorescence originates is 2 x 1CT7 s 1. 

In a very important study of the quartet-doublet reactivity question,72 it was found that ligand-field irradiation of [Cr(CN)6]3 in degassed dimethylformamide results in both phosphorescence from the doublet and substitution of cyanide. In air-saturated solution, however, phosphorescence is quenched completely while the photoreaction is unaffected. The two processes appear to be uncoupled and thus originate from different excited states. The most straightforward conclusion is that the lowest quartet excited state in [Cr(CN)6]3 is the sole precursor to photoreaction. 

The first quantitative photochemical study of a Rh111 amine was reported by Moggi,8 who noted that both 254 nm (LMCT) and 365 nm (ligand field) excitation of [Rh(NH3)5Cl]2+ caused chloride labilization (equation 131). Other early reports include Basolo s study of the photoinduced stereo-retentive halide aquation from [M(en)2X2]+ (M = Rh, Ir X = Cl, Br, I), and Broomhead s observation of chloride aquation from [RhCl2(phen)2]+.726 While halide labilization dominates upon photolysis of [Rh(NH3)5Cl]2+, both bromo and ammine loss occur upon photolysis of the bromo analog (equation 132)685,707 and ammine is labilized from the iodo analog (equation 133).70 Biacetyl sensitization of the bromo complex quenches the biacetyl phosphorescence, but not the fluorescence,707 consistent with a photoreactive triplet state. 

Cobalt(II,III) sepulchrates have been used in the chemical education [415] and considerable number of the chemical and physicochemical studies as efficient quencher of the phosphorescence [416] and electronic excited states [417, 418], as a reductant in kinetic studies of redox reactions [419, 420], as a model for study of magnetodynamic [421], solvent [422] and pressure [423] effects on the outer-sphere electron-transfer reactions. Transfer chemical potentials (from solubility measurements) [424], electrochemical reduction potentials [425] and ligand-field parameters [426] for cobalt sepulchrates have been calculated. Solvent effect on Co chemical shift of cobalt(III) ion encapsulated in the sepulchrate cavity [427]... 

Binding of a paramagnetic, redox-inactive [Cr(CN)6]3- anion to specific sites of a blue copper protein, amicyanin, has been used in NMR-spectroscopic studies of the protein structure in solutions.285Ab initio calculations of the ligand-field spectra of [Cr(CN)6]3 have been performed and the results compared with those for cyano complexes of the other first-row transition metals.286 The role of Cr—C—N bending vibrations in the phosphorescence spectra... 

Typical transition metal complexes with a partially filled d-shell at the metal are characterized by low-energy dd (or ligand field, LF) states [8]. Frequently, these dd states are not luminescent but reactive [9-13]. Ligands are then substituted because LF states are often antibonding with respect to metal-ligand interactions. Nevertheless, a considerable number of transition metal compounds with emissive LF excited states are known. However, in many cases this luminescence appears only at low temperatures. Moreover, spin selection rules are not strictly obeyed, in particular by metals of the second and third transition series. Intersystem crossing is then facifitated and the rate of spin-forbidden emission (phosphorescence) is increased. As a consequence a phosphorescence may also be observed at room temperature. 

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