Energy gap, singlet-triplet

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

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...

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. 

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. 

The first experimental determination of a singlet-triplet energy gap (Mst) for an organic nitrenium ion was made for the 1,3-dimethylbenzotriazolium ion . A powerful ligand, 4,5-bis(diphenylphosphinoyl)-l,2,3-triazole, has been synthesized and found to possess two different modes of chelation <00ACIE3321>. 

Table 1. Calculated Singlet-Triplet Energy Gap (A St> kcal/mol) in Phenylcarbene (la)0...

Andres, J., Safont, V. S., Queralt, J. and Tapia, O A theoretical study of the singlet-triplet energy gap dependence upon rotation and pyramidalization for 1,2-dihydroxy ethylene. A simple model to study the enediol moiety in rubisco s substrate., J. Phys. Chem., 91 (1993), 7888-7893... 

Mixed-valence compounds. The ground state of monomeric species RM (M = B, Al, Ga, In), which have an electron lone pair at the metal center, is singlet and the singlet-triplet energy gap increases with increasing atomic number. Consequently, these compounds are able to act as Lewis bases. Reactions with Lewis-acidic... 

Calculations of the singlet-triplet energy gaps of a series of nitrenium ions [X(H)N ]+ in the gas phase and in solution indicate that the gap decreases in the order X = H > CN > F as a result of stabilization of the singlet state by r-donation from the substituent. For strong tt-donors (Cl, F), the singlet state is more stable than the triplet. ... 

Lastly, the SF approach implemented within the time-dependent. (TD) density functional theory (DFT) extends DFT to multi-reference situations with no cost increase relative to the non-SF TD-DFT. Similarly to DFT and TD-DFT, the SF-DFT model (27) is formally exact and therefore will yield exact answers with the exact density functional. With the available inexact ftmctionals, the SF-DFT represents an improvement over its non-SF counterparts. It has been shown to yield accurate equilibrium properties and singlet-triplet energy gaps in diradicals (27). 

Kohler A, Wilson JS, Eriend RH, Al-Suti MK, Khan MS, Gerhard A, Bassler H (2002) The singlet-triplet energy gap in organic and Pt-containing phenylene ethynylene polymers and monomers. J Chem Phys 116 9457... 

Relationship between Structure and the Singlet-Triplet Energy Gap. 376... 

RELATIONSHIP BETWEEN STRUCTURE AND THE SINGLET-TRIPLET ENERGY GAP... 

TABLE 13.1. Singlet-Triplet Energy Gaps and Geometric Parameters for Simple Nitreninm Ions... 

TABLE 13.2. Singlet-Triplet Energy Gaps in 4-Snbstitnted Phenylnitrenium Ions (X—C6H4NH ) ... 

The parent nitrenium ion (NH2) is firmly established as a ground-state triplet both extensive ab initio calculations as well as PES experiments all agree that the singlet-triplet energy gap is 30 kcal/mol. There have been several investigations on its behavior in solution. Takeuchi et al. " showed that this species could be generated by photolysis of l-amino-(2,4,6-triphenylpyridinium) ion. These photolyses were carried out in the presence of various aromatic compounds. It was found that the triplet state abstracted hydrogen atoms from traps such as toluene... 

Density functional-based theoretical methods have been demonstrated to give highly accurate predictions of nitrenium ions structures, singlet-triplet energy gaps, and vibrational spectra. Future challenges in the area of theoretical predictions include the accurate modeling of nitrenium ion reactions and reaction rates. 

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