Triplet, energy levels, determination state

The triplet energy of thianaphthene 1,1-dioxide was determined by two indirect methods. The first involved the use of several sensitizers of decreasing triplet energy. The results summarized in Table 1 indicate that triplet lies between 53 and 49 kcal mol-1. The second method is more precise and involves the use of thianaphthene 1,1-dioxide as a sensitizer to establish a photostationary state of the a—methylstilbenes. The composition of the photostationary state of a-methylstilbene has been determined as a function of the triplet energy level of the sensitizer. The results indicate a triplet energy for thianaphthene 1,1-dioxide of 50 1 kcal mol-1. Quantum yields of the photodimerization of thianaphthene 1,1-dioxide were determined in benzene as a function of concentration. Oisc is 0.18. The product distribution as a function of solvent polarity demonstrates the ratio of the head-to-head to head-to-tail dimer (HH/HT) increases with the polarity of the solvents. This is consistent with preferential solvatation of the head-to-head transitions state. 

The triplet-state energy level of oxytetracycline, the excitation maximum (412 nm), lifetimes of Eu-OxTc (58 p.s) and Eu-OxTc-Cit (158 p.s), were determined. A 25-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. It s accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu(III) and citrate (C = T lO mol-E ), pH 7.2. Eor determination of citrate, the optimal conditions concentrations of Eu(HI) and OxTc are 1 0,5 (Cg = MO Huol-E-i, = 5-10-HuohE-i) at pH 7.2. 

In contrast to the case of ZnCh-Ceo, no transient formation of Ceo" was detected at 1000 nm for any other dyad in Scheme 4b [65]. In each case, only the triplet-triplet absorption due to the chlorin or porphyrin moiety was observed due to the higher energy of the radical ion pair as compared to the triplet excited state as is expected from the redox potentials. Thus, the energy level of the radical ion pair in reference to the triplet energy of a component is an important factor in determining the lifetime of the radical ion pair. 

Conjugated dienes have very high excited singlet levels, while the excitation energies of the lowest triplet states are less than 60 kcal.276 Intersystem crossing of diene singlets is quite inefficient, so that the chemistry of diene triplets has been determined by photosensitization. 

Photoexcitation of MP-Ceo in Solution. The photoexcitation of MP Cgo in toluene or ODCB results in weak fluorescence at 1.74 eV and a long-lived triplet excited state. The fluorescence quantum yield in toluene is known to be 6 x 10-4 [107]. Singlet excited state lifetimes of 1.45 ns [103] and 1.28 ns [107] have been reported for toluene solutions. The quantum yield for intersystem crossing from MP G eofA i) to MP-Ceo(Ti) is near unity [107] and the lifetime of this triplet state is about 200 (is [103]. The triplet state PIA spectrum of MP Ceo exhibits a Tn <— Ti absorption at 1.78 eV with a characteristic shoulder at 1.54 eV [103]. The energy level of the MP -Coo(7j) triplet state has been determined from phosphorescence to be at 1.50 eV above the ground state level [107]. 

Triplet excited states of four derivatives of ubiquinone-6 (256), in which various ring substituents are progressively altered, have been studied by laser flash photolysis (265 nm) and pulse radiolysis (9—12MeV electrons). The triplet absorption spectra, extinction coefficients, lifetimes, energy levels, and quantum efficiencies of formation were determined.117... 

Fig. 5. Energy level diagram for Pd(2-thpy)2 dissolved in n-octane. The Tj state at 18,418 cm is zero-field split on the order of 0.2 cm. The emission decay times refer to the individual triplet suhstates I, II, and III, respectively, at T = 1.3 K. (Compare Fig. 6.) These suhstates are radiatively deactivated as purely electronic transitions, as well as by Franck-Condon (FC) and Herzberg-Teller (HT) vibrational activity, respectively. This leads the different vibrational satellites. (Compare also Sects. 4.2.2 and 4.2.3.) The lifetime of the S, state is determined from the homogeneous linewidth of the spectrally resolved Sq —> S, electronic origin. (Sect. 3.2) The electronic state at 24.7 x 10 cm is not yet assigned...

The efficiency in the transfer of energy from the triplet states of various compounds to ground singlet states of isoprene, 1,3-pentadiene, and 2,3-dimethylbutadiene have been studied. The diene molecules become excited to their lowest triplet states and undergo chemical reactions which may be dimerization or stereoisomerization. As in the case of butadiene, the energy level of the sensitizer in its lowest triplet state determines the magnitude of the energy that is transferred to the diene and the course of its subsequent reactions. Typically, in the case of... 

The first reported application of the technique by Kessler and Wilkinson [12] in 1981, deals with various aromatic hydrocarbons chemisorbed on Y-alumina. The samples were adsorbed at less than monolayer levels, and the transient spectra observed were shown to be due to triplet-triplet absorptions. Figure 6 shows the time resolved triplet-triplet absorption spectra obtained from 3% coverage of acridine on powdered silica [14] demonstrating the sensitivity of the method and its ability to probe acid-base reactions at catalytic surfaces. Turro and his coworkers [25,26] have studied various molecules on silica surfaces. The lifetimes of the triplet states of valerophenone and diphenyl-butyrophenone adsorbed on powdered silica were determined to be 0.3 and 0.9 [is, respectively [25] which is at least two orders of magnitude greater than in homogeneous solution. Turro et al [26] also demonstrated triplet energy transfer from benzophenone to naphthalene on silica surfaces via static and dynamic pathways. 

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