Photophysical parameters

Table 11 Some photophysical parameters of palladium(II) complexes with increasing aromatic annelation compared with those of the corresponding zinc(II) complexes.176...

Photophysical Parameters of Some Polymer Hosts and Phosphorescent Dopants... 

The photophysical properties (extinction coefficient, shifts in absorption and emission spectra, quantum yield, and lifetime) of a variety of probes are modified by pH changes, complexation by metal ions, or redox reactions. The resulting changes in photophysical parameters can be used to determine concentration of H+ and metal cations with suitably designed fluorophores. Most of these resulting sensors involve an equilibrium between the analyte, A, and the free probe (unprotonated or noncom-plexed by metal ion), Pf. If the stoichiometry of this reaction is 1 1, the reaction may be represented by... 

The S2 state fluorescence of metalloporphyrins was first noticed by Bajema et al. ( ) and later the photophysical parameters concerned with the S2 state were determined on several metalloporphyrins (9,10). S2 - Sq emission from large molecules in condensed phases has also been recognized in many other organic compounds, e.g., azulene (11), thiocarbonyl compounds (12), and several polyenes (13). However, in some metalloporphyrins one can observe the S2 state fluorescence even after the excitation to the state (14-17), that is, the blue... 

Observable photophysical parameters, their relationship to rate constants of various photophysical processes and sources of their information. 

Table 5 Photophysical Parameters for/ac-XRe(CO)3L Complexes in the Uncured and Cured Cycloaliphatic (ERL-4221)/Anhydride Epoxy System at 293 Ka...

Table II. Photophysical Parameters for Some Chromium(III) Complexes... 

TABLE 14. Photophysical Parameters of 87—92 in Butyronitrile and in the Solid State at 77 Ka... 

The emission spectra of homobimetallic and heterobimetallic polymers 89 and 91 in PrCN at 77 K are shown in Figure 41 as examples. Details of the photophysical parameters are presented in Table 14. 

Photophysical parameters of the clusters with double cubane structure. Data are from (Kornienko et al., 2005b ... 

The similarity of the results for 4 and 11 confirms that although porphyrins and chlorophylls have somewhat different absorption spectra and other photophysical parameters, porphyrin-based structures may still be used as valid models for certain aspects of natural photosynthetic energy conversion. 

Table 1 Photophysical parameters of Ir(III) tris-bpy and bis-terpy complexes properties for related complexes of Ru(II) and Os(II) are also listed a...

Because of the generally nonemissive nature of LLCT states, their excited-state properties can be studied only by transient spectroscopy, or indirectly analyzed by their effect on the MLCT excited-state lifetimes of the emissive chromophores. However, if the electron-donor ligand is not stable toward oxidation, then subsequent photochemical reactions may occur. Thus, these irreversible photochemical reactions can be monitored to quantitatively determine the photophysical parameters... 

The photochromism of dihydroindolizines (DHIs) - a new class of photo-chromic molecules - was discovered only in 1979.1,2 These molecules are among the few new photochromes discovered in the past 20 years.3 Their synthetic access has been exploited in detail and their photochemical and photophysical parameters have been studied in a broad sense.3 7 The potential applications are vast and compare favorably with those of the known photochromes.8 The chemistry and photochemistry of the DHIs have been described previously in several surveys.3-7 This review will serve as a short introduction to the field. It will as well include typical preparation modes for the class of dihydroindolizines as well as their aza-homologs, typical five-membered heterocycles. A new class of photochromies derived from these photochromic heterocycles (DHIs) that allows for supramolecular interactions is presented. Some typical applications that are close to commercially useful systems are discussed. 

For a structural correlation of photophysical parameters, the DHI molecule is divided into three regions, i.e., A, B, and C.3 7 Typical partial structures are given in Scheme 13. 

PET-sensitization means that the desired radical pair D + A is produced indirectly by first generating another radical pair D + X using an auxiliary sensitizer X and then exchanging X for A by a thermal electron transfer. X is chosen such that the photophysical parameters and redox potentials bar all other pathways except the PET-sensitized one. Of particular significance for the above mechanistic question is that neither D nor A are excited hence, an exciplex (D A) cannot be formed. Chart 9.2 juxtaposes the direct and the PET-sensitized formation of D- + A-. ... 

In the case of the rhenium(I) bipyridine tricarbonyl complexes with a phosphorous ligand such as 3a in Table I, both the MLCT absorption and the emission bands are blue shifted because of the stronger LF induced by the phosphorous ligand. This causes the lifetime of the MLCT excited state to be longer. The photophysical parameters of some t5rpical Re(I) complexes are smnmarized in Table I (5,26). 

Single-molecule spectra as a function of laser intensity provided details of the incoherent saturation behavior and the influence of the dark triplet state dynamics [33]. Clear heterogeneity in the observed saturation intensity was observed indicating that the individual molecules experience modihcations in photophysical parameters due to differences in local environments. It was also possible to measure the linewidth of single pentacene molecules as a function of temperature in order to probe dephasing effects produced by coupling to a local phonon mode [33]. 

Table 5.2 Observable Photophysical Parameters and their Relationship to Rate Constants of Various Photophysical EYocesses and Sources of their Information ...

Eq. 1. CT = area of the CT-band, LE = area of the locally excited state C = constant that contains all photophysical parameters for both the charge transfer and the locally excited state k, t = rate constant for the formation of the CT -state from the LE-state, this value is strongly dependent on the probe mobility. 

Influence in extension of chromophore conjugation on TPA was studied for the fluorinated polyenes 1-3. Pentafluorosubstitution reduces re-electron density at the left aromatic benzene ring. This results in an electron-deficient substituted benzene with a re-electron density comparable with that of cyanobenzene [341]. This was concluded from the reduction potentials of 1,2,4,5-tetrafluorobenzene (El = -2.4 V vs. SCE [342]) and cyanobenzene = -2.3 V vs. SCE [341]). The larger re-conjugation in 3 causes an increase of e compared to 1 but the change of A/i()] was rather modest compared to the increased size of the chromophore [224]. TPA data and representative photophysical parameters are summarized in Table 3.1. 

The effective photophysical parameter is used in a modified Lambert-Beer relationship (Eq. (51)), where m = mass of the sample, ODm,lx = extinction at the maximum for the optical S0 transition, V = volume, and d = thickness. 

It was noted above that measurements of the lifetime of emission provide an alternative way of accessing the photophysical parameters of a polymer. The analogous approach in CL is to subject the oxidizing polymer to an external perturbation and then observe the change in CL as the system returns to the steady state (George, 1981). This will genemlly take the form of a short period of UV irradiation after which there is a burst of CL followed by decay, which may be analysed according to an assumed kinetic model, such as second-order... 

The photophysical properties of a molecule are influenced by its immediate surroundings. Often the effects follow a qualitative empirical rule or, in favorable situations, a well-established quantitative law. Thus, it becomes possible to use photophysical parameters in order to get insight into the microenvironment (e.g. polarity, viscosity) of the emitting molecule. Fluorescence dyes have been used as molecular reporters, not only in solution, but also in membranes, in the solid state, in mixtures of low molecular compounds or... 

Photophysical and photochemical processes in polymer solids are extremely important in that they relate directly to the functions of photoresists and other molecular functional devices. These processes are influenced significantly by the molecular structure of the polymer matrix and its motion. As already discussed in Section 2.1.3, the reactivity of functional groups in polymer solids changes markedly at the glass transition temperature (Tg) of the matrix. Their reactivity is also affected by the / transition temperature, Tp, which corresponds to the relaxation of local motion modes of the main chain and by Ty, the temperature corresponding to the onset of side chain rotation. These transition temperatures can be detected also by other experimental techniques, such as dynamic viscoelasticity measurements, dielectric dispersion, and NMR spectroscopy. The values obtained depend on the frequency of the measurement. Since photochemical and photophysical parameters are measures of the motion of a polymer chain, they provide means to estimate experimentally the values of Tp and Tr. In homogeneous solids, reactions are related to the free volume distribution. This important theoretical parameter can be discussed on the basis of photophysical processes. 

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