Electronic excitation Jablonski diagram

Figure 7.4 Schematic representation of different competing decay processes and their timescales from the electronically excited state. Diagrams in the form of a Jablonski diagram (left) and in the form of a two dimensional potential energy diagram (right) as a function of two nuclear coordinates.

Figure 10. Electron excitations in radicals (a) Collective representation of one-electron transitions of the A, B, and C types if denotes MO (b) LCI energy-level scheme (Jablonski diagram) for doublet and quartet states indicating why with radicals fluorescence (- - -) but not phosphorescence is observed. Spin-forbidden transitions are represented by dashed lines.

Just as above, we can derive expressions for any fluorescence lifetime for any number of pathways. In this chapter we limit our discussion to cases where the excited molecules have relaxed to their lowest excited-state vibrational level by internal conversion (ic) before pursuing any other de-excitation pathway (see the Perrin-Jablonski diagram in Fig. 1.4). This means we do not consider coherent effects whereby the molecule decays, or transfers energy, from a higher excited state, or from a non-Boltzmann distribution of vibrational levels, before coming to steady-state equilibrium in its ground electronic state (see Section 1.2.2). Internal conversion only takes a few picoseconds, or less [82-84, 106]. In the case of incoherent decay, the method of excitation does not play a role in the decay by any of the pathways from the excited state the excitation scheme is only peculiar to the method we choose to measure the fluorescence (Sections 1.7-1.11). 

Fluorescence is a process that occurs after excitation of a molecule with light. It involves transitions of the outermost electrons between different electronic states of the molecule, resulting in emission of a photon of lower energy than the previously absorbed photon. This is represented in the Jablonski diagram (see Fig. 6.1). As every molecule has different energy levels, the fluorescent properties vary from one fluorophore to the other. The main characteristics of a fluorescent dye are absorption and emission wavelengths, extinction... 

Fig. 6.1. Jablonski diagram, representing electron energy levels of fluorophores and transitions after photon excitation. S = electronic state, different lines within each state represent different vibrational levels. Blue arrows represent absorption events, green arrows depict internal conversion or heat dissipation, and orange arrows indicate fluorescence emission. Intersystem crossing into triplet states has been omitted for simplicity (see also Chaps. 1 and 12).

Fig. 21. Top The general Jablonski diagram for the flavin chromophore. The given wavelengths for absorption and luminescence represent crude average values derived from the actual spectra shown below. Due to the Franck-Condon principle the maxima of the peak positions generally do not represent so-called 0 — 0 transitions, but transitions between vibrational sublevels of the different electronically excited states (drawn schematically). Bottom Synopsis of spectra representing the different electronic transitions of the flavin nucleus. Differently substituted flavins show slightly modified spectra. Absorption (So- - S2, 345 nm S0 -> Si,450nm 1561) fluorescence (Sj — S0) 530 nm 156)) phosphorescence (Ty Sq, 605 nm 1051) triplet absorption (Tj ->Tn,...

Following the absorption of radiation and the promotion of an electron (71 or n) to the vibrationally excited single state S,f (which occurs very rapidly in 10-15s, the dissipation of this energy may take place in a variety of ways itemised below, some of which may be represented diagrammatically by means of a Jablonski diagram (Fig. 2.67(c)). 

An overview of the energetics and possible depletion mechanisms of excited electronic states is named a Jablonski diagram. Herein, singlet states are symbolized by So, Si, S2, and so on, and triplets by T0, Ti, T2, and so on, where the index labels their energetic order and should not be confused with tensor components. A typical Jablonski diagram for an organic molecule is shown in Figure 19. 

Figure 19 Jablonski diagram (schematic) showing the energetic location of the first excited singlet Si and triplet states Ti with respect to the electronic singlet ground state So and possible transitions between them. Radiative transitions are indicated by straight arrows, nonradiative processes by curly ones. Solid arrows represent spin-allowed transitions, dashed-dotted lines spin-forbidden ones.

Figure 16.3 Modified Jablonski diagram ows the energy absorption effects of near metal surface enhanced fluorescence. The process involves o eating an excited electronic singlet state by optical absorption and subsequent emission of fluorescence with different decay paths.

A Jablonski diagram, shown in Fig. 14.11, is a simplified representation of some possible absorption and emission processes in molecules. Assuming that the ground electronic state is a singlet, designated So, absorption of radiation can occiii to several vibrational levels of the lowest excited singlet state Si. Several things can then happen to the excited molecule. One possibility, which we described above for a diatomic molecule, is radiationless relaxation to the lowest vibrational level of Si followed by emission of a photon, usually within several nanoseconds of the absorption. This is fluorescence, which returns the molecule to one of the... 

---