Calculated first singlet excitation

Figure 2. Calculated (INDO/S) first singlet excitation energy all-trans [(CHj)2Si]n (dot-dash) all-Irons [H2Si]n (full) all-gauche [H2Si]n (dashed).

Comparisons of experimental data with the results of calculations using eqns. (11) and (12) has shown that the experimental data can be better described by a model implying electron tunneling from the first singlet excited state of naphthalene, llNh. 

A model for the light/dark behavior of GFP has been proposed [40]. It is based on quantum mechanical calculations of the energy barriers for the cp and z one-bond flips (OBF) and the (p/z hula twists (HTs) that were calculated in the ground and first singlet excited states for a small nonpeptide model compound. Figure 5.5 shows the calculated energy profiles. 

Throughout this paper the HPHF model is described and applied to determine the optimal geometry of the first singlet excited state of some molecular systems. The procedure yields only one electronic state in each calculation but it is found to converge quickly. The results are in relatively good agreement with the available experimental data. The procedure permits also the use of different basis sets for the different states. 

Relative pK calculations are also useful to predict the acidity of electronically excited species, taking the ground-state value as reference. Gao et al. [59] used the TCI cycle to predict the pK of the first singlet excited state of phenol (PhOH ). The calculations were performed using a hybrid quantum mechanical and molecular mechanical method (QM/MM) where the solute is treated quantum mechanically while the solvent molecules are represented by an MM force field. They obtained a ApK (PhOH PhOH ) of —8.6 + 0.1 pK units, implying a pK value of 1.4 for PhOH. ... 

As an illustration of the performance of TDDFT, we compare various density functionals and wave function methods for the first singlet excited states of naphthalene in Tables 4, 5, and 6. All calculations were performed using the aug-TZVP basis set, while the complete active space self-consistent field (SCF) with second-order perturbation theory (CASPT2) results from Ref. 200 were obtained in a smaller double-zeta valence basis set with some diffuse augmentation. The experimental results correspond to band maxima from gas-phase experiments however, the position of the band maximum does not necessarily coincide with the vertical excitation energy, especially if... 

The results of these calculations show that the excited states of benzene fall into three classes covalent, ionic, and Rydberg. An example of a covalent state is the first singlet excited state, B2 , lying at an energy of 4.90 eV above the ground state. It may be represented to an excellent approximation simply as ... 

The output of the calculation will be the new CASSCF description of the triplet state. We will use this as the starting point for further calculations first, another CAS on the triplet with the target basis set, and then a CAS on the singlet excited state ... 

This situation occurs when excitation brings the fluorophores to an excited state other than the first singlet state from which fluorescence is emitted. Let a be the angle between the absorption and emission transition moments. The aim is to calculate cos dE and then to deduce r by means of Eq. (5.20). 

It has been known experimentally(4) that much of the second order susceptibility generally arises from the lowest singlet excited state. For any particular molecule, the recently introduced Missing States Analysis (MSA)(5,6). can show, via calculation, to what extent P is dominated by the first excited state. For instance, the P of p-nitroaniline has been shown by MSA to be heavily dominated by the first excited state, at least with a PPP (Pariser-Pople-Parr) Hamiltonian and standard basis. The result of these findings is that one can often approximate Equation (4) by including only one excited state in the sum, there-by arriving at a two-level model ... 

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