Doublet states, excited

Consider an atomic system with a singlet ground state a and doublet excited states b, the members of which are denoted by by and b2. The Hamiltonian for the states (ils b2) is assumed to be... 

Manipulation of Doublet Excited State Lifetimes in Chromium (III) Complexes... 

The relaxation rates observed for the lowest energy doublet excited states ( E) of chromium Ill) complexes can be represented, kre k°... 

In this report we describe some of the studies which have been initiated to investigate the factors contributing to the behavior of the lowest doublet excited state in chromium(III). The principle goal of our work has been to explore those steric constraints, introduced by the ligands, which greatly alter the photophysical properties of the 2E excited state. In pursuit of this goal, we have re-investigated some features of well known amine and polypyridyl complexes in order to obtain internally consistent reference systems. 

In point of fact, values of Ttr are not well defined for the trans-Cr(N4)(CN)2 complexes, since their doublet excited states are strongly quenched by OH", even in moderately acidic solutions (Figure 4). It is clear that Ttr for the OH" -independent pathway is wejl above room temperature e.g. Ttr 2 360 K for Crans-Crdiii) (CN) 2 complexes. The N-deuterated analogs have somewhat smaller values of Ttr in D2O (CH3CO2D),... 

ENDICOTT ET AL. Doublet Excited State Lifetimes in CrComplexes... 

The ground state electronic configuration (A,) and doublet excited state ( B,) are estimated by analogy with those for N0 ... 

The Walsh correlation diagram (6) predicts a ground state electronic configuration of A for a 21 valence electron molecule. In addition, the existence of two doublet excited states is highly probable. We omit these excited states since no spectroscopic information is available on these states for isoelectronic molecules which would allow us to estimate the relative term values. 

Quenching of the ( CT)[Ru(bipy)3] by [Cr(bipy)]3 has been studied. This is via electron transfer to the Cr complex and a rapid back reaction. The ruthenium complex will also quench the 727 nm emission of the metal-centred doublet excited state of the chromium species, by a similar mechanism. Evidently both ligand- and metal-centred excited states can be quenched by bimolecular redox processes. A number of Ru complexes, e.g. [Ru(bipy)3] and [Ru(phen)3] also have their luminescence quenched by electron transfer to Fe or paraquat. Both the initial quenching reactions and back reactions are close to the diffusion-controlled limit. These mechanisms involve initial oxidation of Ru to Ru [equation (1)]. However, the triplet excited state is more active than the ground state towards reductants as well as... 

Figure 21. A simplified generalized state diagram for the photoreactions of Cr111 complexes, where Q e is the Franck Condon quartet state formed by vertical excitation, Ql and D0 are the thermally equilibrated quartet and doublet excited states, kn, kr, and kp are the decay pathways direct from the doublet, and k n and k p are the decay pathways from Qj.

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