Jablonski diagrams

FIGURE 7.4 Modified Jablonski diagram showing transitions between excited states and the ground state. Radiative processes are shown by straight lines, radiationless processes by wavy lines. IC = internal conversion ISC = intersystem crossing, vc = vibrational cascade hvf = fluorescence hVp = phosphorescence. 

Jablonski (48-49) developed a theory in 1935 in which he presented the now standard Jablonski diagram" of singlet and triplet state energy levels that is used to explain excitation and emission processes in luminescence. He also related the fluorescence lifetimes of the perpendicular and parallel polarization components of emission to the fluorophore emission lifetime and rate of rotation. In the same year, Szymanowski (50) measured apparent lifetimes for the perpendicular and parallel polarization components of fluorescein in viscous solutions with a phase fluorometer. It was shown later by Spencer and Weber (51) that phase shift methods do not give correct values for polarized lifetimes because the theory does not include the dependence on modulation frequency. 

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.

Figure 9.1. A Jablonski diagram. So and Si are singlet states, Ti is atriplet state. Abs, absorption F, fluorescence P, phosphorescence IC, internal conversion and ISC, intersystem crossing. Radiative transitions are represented by full lines and nonradiative transitions by dashed lines...

Figure 6. Jablonski diagram for the excited-state proton transfer and energy dissipation in TIN kSo s0> ks,s,-, kT,Tl- rate constants of proton-transfer processes in the ground state, first excited singlet state, and triplet state, respectively, and k,j rate constants of radiationless deactivations and k,- rate constants of intersyslem...

Fig. 1 Jablonski diagram of energy level for describing processes absorption, fluorescence and phosphorescence in complex molecules where kf and /c arc the radiative and nonradiative rates of fluorescence, respectively, kj and kTnr are the radiative and nonradiative rates of phosphorescence, respectively, k-lsc is the interconversion rate, and kmt is the rate of intermolecular processes Av denotes the Stokes shift of fluorescence...

Fluorescent molecules can participate in different intermolecular reactions starting from Si state with rate klnl as a result, their properties, such as the quantum yield, , and the fluorescence lifetime, x, can change. The proper equations for x and , as illustrated in Jablonski diagram (Fig. 1), may be written as [1, 2] ... 

Figure 3 Type I and type II photooxidation processes with a porphyrin sensitizer illustrated with a modified Jablonski diagram. (S0 = ground singlet state, Si = first excited singlet state, S2 = second excited singlet state, T,i— ground triplet state, Ti = first excited triplet state, i.s.c. — intersystem crossing.)...

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,...

Figure 1 Jablonski diagram showing energy levels and transitions F, fluorescence C, chemiluminescence P, phosphorescence CD, collisional deactivation IC, internal conversion ISC, intersystem crossing S0, ground singlet state S1( S2, excited singlet states Tl5 excited triplet state.

Figure 2. Jablonski diagram for the photochemical interconversion of la and 3a. The energies (in kcal/mol) of various electronic states were obtained from spectroscopic data or by quantum chemical calculations (in italics) using CISD+Q/6-31 G(d) and B3LYP/6-31 G(d) calculations for Ti -3a.

The most populated energy state of chemical species at room temperature is the ground state. Once a molecule has absorbed energy in the form of electromagnetic radiation, it returns to the ground state, which can occur via several routes, some of which are shown in the Jablonski diagram (Fig. 9). 

Fig. 9. Jablonsky Diagram for energy conversion pathways of an excited molecule. While fluorescence occurs between states of the same spin, an ISC (inter system crossing) leads to spin inversion and a delay in emission (phosphorescence halftimes from 1CT4 s to minutes or even hours)...

The principle of the electronic processes in molecules can be schematically illustrated with the classical Jablonski diagram, which was first proposed by Prof. A. Jablonski in 1935 to describe absorption and emission of light. Figure 3.8 illustrates the electronic processes of the host-guest molecules. 

Explain the processes of absorption, radiative transitions and radiationless transitions in terms of Jablonski diagrams. 

The properties of excited states and their relaxation processes are conveniently represented by a Jablonski diagram, shown in Figure 3.2 and summarised in Table 3.1. 

Figure 3.2 Jablonski diagram for an organic molecule, illustrating excited-state photophysical processes...

Figure 4.12 Jablonski diagram for the deactivation of a molecule by emission of E-type delayed fluorescence...

The Jablonski diagram for thermally-activated delayed fluorescence is shown in Figure 4.12. 

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