Singlet-triplet energy splitting

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. 

In order to increase the experimental benchmarks available for comparison with theoretical calculation, Mcllroy et al., determined the singlet triplet energy splitting in a diaminosubstituted nitrenium ion, 1,3-dimethylbenzotriazolium ion 37 (Fig. 13.22). This species can be viewed a nitrenium ion by virtue of mesomer 37a, which places a positive charge on the central nitrogen. Because this species... 

Accordingly, the singlet-triplet energy splitting is slightly enlarged... 

TABLE 37. Calculated and experimental (in parentheses) geometries and singlet-triplet energy splittings (A st) of MH2 and MX2 (X = halogens) metallylenes"... 

They found that, as the box radius is reduced, the singlet-triplet energy splitting increases, as can be seen in Figure 4. 

Hydroxytetramethylene (12), the 1,4-biradical intermediate in the Norrish type II reaction, has been studied by 2-in-2 MCSCF calculations and all possible gauche and trans minima have been located on the singlet and triplet PE surfaces [45]. The singlet-triplet energy splitting and SOC values vary with the conformational geometry and have no correlation to the distance between the two radical... 

The photophysical investigation of the exciplex formed between 4,4, 4"-tris[3-methylphenyl(phenyl)amino] triphenylamine (m-MTDATA) and 2-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-l,3,4-oxadiazole (PBD) in a 50 50 blended film showed that the mechanism behind extra singlet production was consistent with the photoluminescence being enhanced via thermally activated delayed fluorescence (E-type nature). Measurements of the emission intensity change with temperature were used to estimate the exciplex singlet-triplet energy splitting to be around 5 meV. 

Kobori Y, Akiyama K and Tero-Kubota S. Theoretical Analysis of Singlet-Triplet Energy Splitting Generated by Charge-Transfer Interaction in Electron Donor-Acceptor Radical Pair Systems. J. Chem. Phys. 2000 113 465-468. 

As the CCC angle at the carbene center is larger than in 5, a smaller singlet-triplet energy splitting is expected. The B3LYP/6-311+G level gives To =-5.8 kcal mol" this value increases to —8.5 kcal mol" when corrected with equations (1) to (3). 

Hayden, C.C., D.M. Neumark, K. Shobatake, R.K. Sparks, and Y.T. Lee (1982), Methylene singlet-triplet energy splitting by molecular beam photodissociation of ketene, J. Chem. Phys., 76, 3607-3613. 

---