Highest occupied molecular orbitals HOMOs . electron promotion

This type of probe, often called fluorescent photoinduced electron transfer (PET) sensors, has been extensively studied (for reviews, see Refs. 22 and 23). Figure 2.2 illustrates how a cation can control the photoinduced charge transfer in a fluoroiono-phore in which the cation receptor is an electron donor (e.g., amino group) and the fluorophore (e.g., anthracene) plays the role of an acceptor. On excitation of the fluorophore, an electron of the highest occupied molecular orbital (HOMO) is promoted to the lowest unoccupied molecular orbital (LUMO), which enables photoinduced electron transfer from the HOMO of the donor (belonging to the free cation receptor) to that of the fluorophore, causing fluorescence quenching of the latter. On... 

In the first excited state, an electron in one of the highest occupied molecular orbitals (HOMOs) is promoted to one of the lowest unoccupied molecular orbitals (LUMOs), increasing the energy of the molecule by 2. This transition can be observed spectroscopically, and the value of fi can be determined. 

Figure 14.12 Ultraviolet excitation of 1,3-butadiene results in the promotion of an electron from i / , the highest occupied molecular orbital (HOMO), to 1//3, the lowest unoccupied molecular orbital (LUMO).

The observed femtosecond dynamics of this dissociative CT reaction is related to the nature of bonding. Upon excitation to the CT state, an electron in the highest occupied molecular orbital (HOMO) of benzene (ir) is promoted to the lowest occupied molecular orbital (LUMO) of I2 (a ). Vertical electron attachment of ground state I2 is expected to produce molecular iodine anions in some high vibrational levels below the dissociation limit. In other words, after the electron transfer, the I—I bond is weakened but not yet broken. While vibrating, the entire I2 and benzene complex begins an excursion motion within die coulombic field and the system proceeds... 

In order to perform ah initio molecular dynamics in excited states, the forces on the atoms are computed on the fly. There are two different implementations of force calculations for the two TDDFT schemes, P-TDDFT and LR-TDDFT. In the first case, the excited state is obtained with the promotion of one electron from the highest occupied molecular orbital (HOMO) to a selected unoccupied molecular orbital (the lowest one, LUMO, in our case). The corresponding KS excited single-determinant configuration is taken for the computation of the electronic density, which is then used to compute the forces on the atoms according to the Hellmann-Feynman electrostatic theorem [35]... 

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