Triplet spectrum

Fermi golden rule, 268 Filipescu, N., 291 Fisch, M. H., 307 Fischer, F., 379 Flash photolysis, 80-92 of aromatic hydrocarbons, 89, 90 determination of jsc, 228-230 determination of triplet lifetime, 240-242 energy of higher triplet levels, 219-220 flash kinetic spectrophotometry, 82, 83 measurement of triplet spectra, 81,82 nanosecond flash kinetic apparatus, 89 nanosecond flash spectrographic apparatus, 88... 

FIGURE 11.1 Schematic triplet spectra as a function of zero-field splitting. The X-band S = 1 spectra have been calculated for indicated /l-values and with E = D/10 to illustrate increasing intensity of the IAm5l = 2 transition at half field with increasing D-value. 

One of the first applications of this chopped-beam irradiation technitriplet spectra was reported by Labhart From a knowledge of the intensity of the irradiation light, he determined the quantum yield of triplet generation to be 0.55 0.11 for outgassed solutions of 1,2-benzanthrazene in hexane at room temperature. Hunziker 32) has applied this method to the study of the gas-phase absorption spectrum of triplet naphthalene. A gas mixture of 500 torr Na, 0.3 mtorr Hg, and about 10 mtorr naphthalene was irradiated by a modulated low-pressure mercury lamp. The mercury vapor in the cell efficiently absorbed the line spectrum of the lamp and acted as a photosensitizer. The triplet state of naphthalene was formed directly through collisional deactivation of the excited mercury atoms. 

Finally, the S - Sq and Tm -Ti absorption spectra of 15 conjugated hydrocarbons were calculated by Pancir and Zahradnik 45,4C) using a modified semiempirical parameter set. Their description of the singlet-triplet and triolet-triplet spectra achieves about the same accuracy as the PPP method for singlet-singlet spectra. 

The oxygen-perturbed singlet-triplet spectra of aromatic carbonyl compounds were investigated by Warwick and Wells (Fig. 23). Transitions to states were enhanced by the perturbing agent while transitions to (n,7t ) states remained unaffected. It should be mentioned, however, that Evans also observed an oxygen-perturbed increase of the intensity of the Tnn So transitions in pyrazine and acridine. 

Hoijtink, G. J. Triplet-triplet spectra of alternant hydrocarbon molecules. Pure Appl. Chem. 11, 393 (1965). 

Pancir, J., Zahradnik, R. Theoretical study of singlet-triplet and triplet-triplet spectra. 

A.-T. Wu, et have very recently observed triplet spectra from the... 

If molecular gases are considered, infrared spectra richer than those seen in the rare gases occur. Besides the translational spectra shown above, various rotational and rotovibrational spectral components may be expected even if the molecules are non-polar. Besides overlap, other induction mechanisms become important, most notably multipole-induced dipoles. Dipole components may be thought of as being modulated by the vibration and rotation of the interacting molecules so that induced supermolecular bands appear at the rotovibrational frequencies. In other words, besides the translational induced spectra studied above, we may expect rotational induced bands in the infrared (and rotovibrational and electronic bands at higher frequencies as this was suggested above, Eq. 1.7 and Fig. 1.3). Lines at sums and differences of such frequencies also occur and are common in the fundamental and overtone bands. We will discuss the rotational pair and triplet spectra first. 

Although the triplet spectra and the ISC quantum yield of oligothiophenes are well characterized, the location of the lowest triplet state Ti could not be determined in solution and in isolated molecules so far because of a lack of phosphorescence (95PAC9 96JPC18683). Attempts have also been made to detect an So-Ti transition by absorption measurements in highly concentrated solutions, but these attempts were not very successful. The only So-Ti spectrum that has been reported was measured for 3T (90PP(52)655). 

The lowest triplet spectra for some benzenoid hydrocarbons... 

The optical absorption, measurable via the excitation spectra of secondary emissions (delayed fluorescence,143 phosphorescence,142 EPR triplet spectra,166 etc.). The absorption is the response of the crystal to an excitation spatially homogeneous at the microscopic scale ... 

Recently, the response theory formalism was applied for the calculation of singlet-triplet spectra in polyenes and aromatic hydrocarbons [83,133,134,132]. In this section we shall discuss mainly the vertical Tn <— So transitions probability in polyenes. The minimum level of accuracy includes CAS calculations of the ground state correlating all x electrons followed by linear and quadratic multi-configuration response calculations. Because the ethene molecule is the simplest representative of unsaturated hydrocarbons, different types of active spaces and AO basis sets were tested more thoroughly for this molecule in order to study the convergence of the S-T transition probability with respect to the level of accuracy. 

Triplet, radical anion, and radical cation spectra of furocoumarins have been determined by flash photolysis and pulse radiolysis. Triplet spectra are modified by hydrogen bonding and in water the triplets may be regarded as exciplexes. " The triplet states, semi-oxidized and semi-reduced radicals of haematoporphyrin, and three O-acyl derivatives have also been characterized. Triplet-state participation of several 4-hydroxy- and 4-methoxybenzothiazoles has been studied by flash photolysis. " These compounds are models for pheomelonin. 

Triplet-Triplet Spectra of Aromatic Molecules in Mixed Crystals. 

This chapter, far from being exhaustive, is aimed at outlining the properties of the radical ions and of the free radicals derived from photochromic compounds independently of whether or not these paramagnetic species are involved in the photochromic process itself. In particular, it will deal with the EPR of dihydro-and dialkyldipyridyl radical cations (viologens) and of the radical anions of a variety of nitro-substituted spirofmdoline-benzopyrans], spiro[indoline-naphtho-pyrans], and spiro[indoline-naphthoxazines] as well as their triphenylgermyloxy nitroxides and with the triplet spectra observed upon irradiation of 2,2,4,4-tetrachloro-1 -keto-1,4-dihydronaphthalene. 

It is not surprising that the triplet states of porphyrins attract interest. A comprehensive study of some purpurins with Sn(lV) substitution involving observations of absorption, fluorescence and triplet spectra and 2 formation and the triplet state of sapphyrin dication (a large porphyrin like system) shows an unusual spin alignment in the monomer and spin delocalization in dimers " are systems of photophysical interest. The influence of external parameters on time resolved transient hole burning in porphyrins shows the effects of a triplet state bottleneck in the rate of state build up". ... 

ORD measurement, deg cm /dmol temperature (c.g., in Curie—Weiss expressions) metric ton triplet (spectra) triton... 

Earlier reports on carotenoid triplet spectra in site-directed mutants found appreciable Car population at temperatures as low as 6 K in the heterodimer mutant M200(His Leu) of Rb. capsulatus (Bylina et al, 1990). This agrees well with the notion of Be acting as a bridging molecule since in the hetero-... 

In the case of Fe the external field acts as a pertubation on the quadru-pole splitting, but this is not necessarily true for Sn so that the observed spectra are more complicated than the doublet-triplet spectra of the former. In Figs. 14.5 and 14.6 are shown some typical computed curves for a random polycrystalline sample with e qQ positive in sign, t] = 0, and /f either parallel or perpendicular to the axis of observation [45]. Appreciable asymmetry is not seen for quadrupole splittings of less than 1 mm s and fields of less than 30 kG, so that the sign of e qQ is not determined under these conditions. The asymmetry parameter has almost no effect for values of rj less than 0-6 and can only be determined in rare circumstances. 

The intersystem crossing efficiencies of 3 and 21 were very small (1%). The triplet-triplet spectra of these dyes were obtained using the triplet-triplet energy transfer method, employing 9,10-dibromoanthracene (DBA) as the sensitizer (Fig. 4). The transient absorption spectrum, recorded immediately af-... 

Figure 3.3. Flash spectrographic measurement of triplet spectra. (Adapted from Porter. )...

Table 9.8. Second-Order Spin-Orbit Selection Rules for the Appearance of Ungerade Vibrations in Singlet-Triplet Spectra...

Fig. 9.1. Typical triplet spectra of nitroxide radicals in most of spin-label or spin-probe studies (upper) A, rigid state B, rapid motion.

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