Level scheme singlet-triplet

Scheme 1 Electronic states involved in the absorbtion bands in the region of the first singlet—triplet intersection for octahedral, tetragonal and trigonal complexes of nickel(II).336 Solid arrows denote spin-allowed absorbtion transitions, dotted arrows connect pairs of interacting levels. (reprinted with permission from ref. 336 1998, American Chemical Society).

The level schemes for [Ru(phen)3] and [Os(phen)3] (phen == 1,10-phenanthroline) are representative of the clusters of low lying electronic states that arise from dv configurations of many ruthenium (II), osmium (II), and iridium (III) complexes. They are highly unusual since they have decay parameters that lie between the ranges expected for conventional singlet and triplet states and because of the magnitudes of the splittings themselves. These parameters control the nature of dir" ... 

Figure 6. Energy level scheme for a typical aromatic hydrocarbon. So denotes the electronic ground state, S the first excited singlet state and T the first excited triplet state. The triplet state is actually split into three sublevels by magnetic dipolar interaction of the triplet electrons (zero-field splitting). The dots and arrows denote the approximate populations and lifetimes of the sublevels for a typical, planar aromatic hydrocarbon. The lower panel shows schematically the time distribution of fluorescence photons (photoelectric pulses) for a single emitter undergoing singlet-tiiplet transitions leading to photon bunching.

Fig. 20 Energy level scheme and electronic transitions in 35. Upon excitation (ex) of HBC, either singlet energy transfer (EET) to the PMI periphery or intersystem crossing (ISC) to the HBC triplet state (Tj) occurs. In the case of EET, PMI fluorescence ( / ) is observed while population of Ti leads to a dark state. After ISC, singlet-triplet annihilation (STA) may quench excited singlet states (Si) of the PMI periphery through energy transfer to Ti. Subsequently, in this example, the higher excited triplet state (r ) decays non-radiatively...

The first term of Eq. 4 represents the electronic Zeeman term, Si and 2 the spin operators for tvro triplet carbenes, and the second term represents the electronic exchange interaction. If Si and 2 couple to a quintet state (S = 2), ( 1 + 2) = S = S(S + 1) = 6. If they couple to a singlet, S = 0. Therefore, this term directly results in the energy level scheme, indicated in the inset of Fig. 9.13. The pure singlet and the pure quintet states are split by Assq which turns out to be the characteristic property of each dicarbene. The third term of Eq. 4 represents the magnetic dipole-dipole coupling of the two triplet carbenes ... 

Optical limiting by materials exhibiting RSA has been widely studied. - These materials, for example, C60 molecules, possess a molecular energy level scheme as depicted in Figure 12.27, in which the excited state absorption cross sections G] (of the singlet state) and/or CTj of the triplet excited state are greater than the ground state cross section ct. ... 

Figure 7.8 Energy levels and relevant coupling scheme for singlet-triplet coupling with virtual transition between two triplet states caused by vibronic interactions.

---