Excited molecules nomenclature

Figure Al.6.20. (Left) Level scheme and nomenclature used in (a) single time-delay CARS, (b) Two-time delay CARS ((TD) CARS). The wavepacket is excited by cOp, then transferred back to the ground state by with Raman shift oij. Its evolution is then monitored by tOp (after [44])- (Right) Relevant potential energy surfaces for the iodine molecule. The creation of the wavepacket in the excited state is done by oip. The transfer to the final state is shown by the dashed arrows according to the state one wants to populate (after [44]).

Before extending this discussion, it is essential to provide a very brief indication of the nomenclature used to describe the electronically excited states of molecules, not only because it is convenient to be able to specify the states under discussion, but also because the types of excitation that are possible become revealed. 

AHOMO and ALUMO may be derived from a perturbational treatment of the union of the [I l]annulenyl cation and C or of the [I3]annulenide anion and C , respectively. This also shows that these molecules have further excited states in addition to those derived from a (4N + 2)-electron perimeter. This is true for the longest-wavelength transitions of both molecules, which therefore cannot be labeled within the framework of Platt s nomenclature. Hence, a prediction of their MCD sign on the basis of the perimeter model is also impossible. However, the next two bands correspond to the L, and Lj states of a (4Af + 2)-electron perimeter and show the expected behavior in the MCD spectra. In acenaphthylene the order of the B terms is -, + and in pleiadiene -f-, -. These signs are not changed by perturbing substituents since the difference between AHOMO and ALUMO is too large. Both molecules represent hard chromophores. 

We adopt the nomenclature of molecular spectroscopy to describe the excitation and relaxation processes in PPV derivatives, since the polymer photophysics is similar to the photophysics of large organic molecules [146]. Figure 22.11 shows schematically the configuration coordinate diagram of all... 

The l Bzu excitation is polarized along the short axis of the naphthalene molecule. In Platt s nomenclature of excited states of polycyclic aromatic hydrocarbons (PAHs), l Bzu corresponds to the La state, which has more ionic character than the 1 B3 (or Lj,) state. Parac and Grimme have pointed... 

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