Triplet energies

The CNDO and CNDO/S methods apply the ZDO approximation to all integrals, regardless of whether the orbitals are loeated on the same atom or not. In the INDO method, whieh was designed to improve the treatment of spin densities at nuelear eenters and to handle singlet-triplet energy differenees for open-shell speeies, exehange integrals... 

However, contrary to expectation, triplet (6) was formed in 17% yield when its triplet energy was less than that of (3) (R = phenyl), and triplet (6) was still formed in 12% yield when ketone (5) (R = P-naphthyl) had the lower triplet energy. The n — tt triplets, such as (6) might be favored over n — tt triplets, such as (5) (R = P-naphthyl), even when energy considerations would indicate the opposite (26). 

TTie photoreduction can be quenched by known triplet quenchers. The effecti e quenchers are those which have T] states less than 69kcal/moI above S,. Quenchers with higher triplet energies are ineffective because the benzophenone n-n triplet is then not sufficiently energetic to effect energy transfer. 

Dimethylenefuran-, 3,4-dimethylenethiophene- and 3,4-dimethylenepyr-rolediyl radicals as non-Kekule molecules with tunable singlet-triplet energy spacings 97ACR238. 

Unusual photophysical properties of polyazaanthracenes and polyazapentacenes having low values of calculated singlet-triplet energy gap 99PAC295. 

Table 2. Singlet-triplet energy separations (AEsx) in M-H monomers, M—M bond dissociation energies (BDEs), SCF calculated bond lengths for the hypothetical, linear dimers HMMH (M = B, Al, Ga, In, or Tl) ...

Fig. 3 A schematic illustration of through-bond and through-space interactions between the radical centers. The singlet-triplet energy gap, the activation energy (E, and the energy...

Table 1 Spin preference of ground state and the calculated singlet-triplet energy separation of some selected Jt-conjugated diradicals...

Phosphinidenes have either a singlet ground state with two lone pairs and an empty p-orbital on the phosphorus atom or a triplet ground state in which the phosphorus has instead one lone pair and two singly occupied p-orbitals. Not surprisingly, the electronic preference, i.e., the singlet-triplet energy gap (AEst) and thus the stabUity and reactivity of a phosphinidene, is determined by its substituent. 

Table 1. Bond lengths (A) and singlet-triplet energy differences (in kcal/mol) for triplet phosphinidenes ...

Table 2. Singlet-triplet energy differences (A sx) and singlet (BDEj), triplet (BDEx), and composite (BDEsx/xs) bond dissociation energies for phosphinidenes and their W(CO)5 complexes, calculated with BP/TZP...

As demonstrated in the two previous sections, TRIR spectroscopy can be used to provide direct structural information concerning organic reactive intermediates in solution as well as kinetic insight into mechanisms of prodnct formation. TRIR spectroscopy can also be used to examine solvent effects by revealing the inflnence of solvent on IR band positions and intensities. For example, TRIR spectroscopy has been used to examine the solvent dependence of some carbonylcarbene singlet-triplet energy gaps. Here, we will focns on TRIR stndies of specific solvation of carbenes. 

Singlet-triplet Energy Splittings in Carbenes and Diradicals 229... 

A list of singlet-triplet energy splittings measured using photoelectron spectroscopy is give in Table 5.4. 

A number of experimental techniques are available for the determination of triplet energy levels. Those most commonly employed are phosphorescence spectroscopy, phosphorescence excitation spectroscopy, singlet to triplet... 

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