Benzene, absorption spectrum triplet excited

Example 5.4-1 The absorption spectrum of benzene shows a strong band at 1800 A, two weaker bands at 2000 A and 2600 A, and a very weak band at 3500 A. As we shall see in Chapter 6, the ground state of benzene is 1A, and there are singlet and triplet excited states of Btu, B2u, and Elu symmetry. Given that in D6h, (x, y) form a basis for Elu and z transforms as A2u, find which transitions are allowed. 

Taking advantage of the fact that the triplet state of metalloporphyrins with tetrabenzopor-phyrin (H2TBP or H2I, fig. 10) lies around 12 500 cm-1, a team from Minsk succeeded in sensitizing Ybm luminescence in solutions of [Yb(TBP)L], where L = Cl or acac (acetyl-acetonate), in several solvents like benzene, dimethylformamide (dmf), pyridine, quinoline or a mixture of octane and benzene (Kachura et al., 1974). Energy transfer from the porphyrin chromophore was ascertained by the excitation spectrum of the Ybm luminescence being identical to the absorption spectrum of the complex. In benzene, the quantum yield of... 

This description of the relative spectral linewidths of the lowest excited toi states applies to the whole family of aromatic hydrocarbons. It also applies to the manifold of triplet jui states. In the case of benzene, Burland, Castro and Robinson 24> and Burland and Castro 25> have used phosphorescence and delayed fluorescence excitation techniques, respectively, to measure the absorption spectrum of the lowest triplet state, 3Biu of ultrapure crystals at 4 K. The origin is located at 29647 cm-1. Unlike all the earlier studies on the lowest singlet triplet absorption spectrum, this was not an 02 perturbation experiment. Here widths of less than 3 cm-1 were obtained. This result should be compared with the much broader bands 150-1 observed for the suspected second triplet ZE i in 5 cm crystals of highly purified benzene 26>. The two triplet states are separated by 7300 cm"1. 

Biczok, L, Linschitz, H., and Walter, RL, Extinction coefficients of fullerene triplet and anion radical and one-electron reduction of the triplet by aromatic donors, Chem. Phys. Lett., 195,339,1992. Dimitrijevic, N.M. and Kamat, P.V., Triplet excited state behavior of fullerenes pulse radiol) is and laser flash photolysis of fullerenes (C60 and C70) in benzene, /. Phys. Chem., 96,4811, 1992. Bensasson, R.V., Hill, T., Lambert, C., Land, E.J., Leach, S., and Truscott, T.G., Pulse radiol) is study of buckminsterfuUerene in benzene solution. Assignment of the 60 triplet-triplet absorption spectrum, Chem. Phys. Lett., 201, 326, 1993. 

When polyvinylbenzophenone is irradiated at 365 nm in benzene solution containing 0.1 mole l1 isopropanol, photoreduction occurs as demonstrated by the formation of acetone and the disappearance of the carbonyl absorption in the infrared spectrum [65]. The reaction is assumed to proceed by a mechanism similar to that of the photoreduction of benzophenone, which involves the excited triplet state of the ketone ... 

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