Singlet excited state absorption

Vivas, M., Fernandes, R. Mendonca, R. (2012). Study of singlet excited state absorption spectrum of lutetium bisphthalocyanine using the femtosecond Z-scan technique Chemical Physics Letters 531, 173-176. 

Not only the stationary band maxima of absorption and fluorescence match this formula but also the radical absorption and even the triplet and singlet excited state absorption. Thereby the fitting parameters have been altered. 

Hilinski, E.F., McGowan, W.M., Sears, D.F., Jr., and Saltiel, J., Evolutions of singlet excited-state absorption and fluorescence of all-frflns-l,6-diphenyl-l,3,5-hexatriene in the picosecond time domain,/. Phys. Chem., 100, 3308-3311, 1996. 

Fluorescence from the ExcitedSj State. In Figure 1, after absorption (A) and vibrational deactivation (VD) occur, the lowest or nearly lowest level of the singlet excited state is reached. If the molecule is fluorescent with a high quantum efficiency, fluorescent emission of a quantum of... 

Anthraquinones are nearly perfect sensitizers for the one-electron oxidation of DNA. They absorb light in the near-UV spectral region (350 nm) where DNA is essentially transparent. This permits excitation of the quinone without the simultaneous absorption of light by DNA, which would confuse chemical and mechanistic analyses. Absorption of a photon by an anthraquinone molecule initially generates a singlet excited state however, intersystem crossing is rapid and a triplet state of the anthraquinone is normally formed within a few picoseconds of excitation, see Fig. 1 [11]. Application of the Weller equation indicates that both the singlet and the triplet excited states of anthraquinones are capable of the exothermic one-electron oxidation of any of the four DNA bases to form the anthraquinone radical anion (AQ ) and a base radical cation (B+ ). 

Fig. 2 Jablonski energy level diagram illustrating possible transitions, where solid lines represent absorption processes and dotted lines represent scattering processes. Key A, IR absorption B, near-IR absorption of an overtone C, Rayleigh scattering D, Stokes Raman transition and E, anti-Stokes Raman transition. S0 is the singlet ground state, S, the lowest singlet excited state, and v represents vibrational energy levels within each electronic state.

Carotenoids are characterised by two low lying singlet excited states. The S2( Eu) state has a high absorption dipole strength and is very weakly fluorescent ( F 10 -10 ) [200, 201-204], The state is dipole forbidden... 

The transient absorption formed from laser flash photolysis of 15 was not quenched in oxygen-saturated solutions, presumably because the photoenolization to form 16 takes place from a singlet excited state of 15. Furthermore, Schworer and Wirz did not observe any transient absorption that can be attributed to the formation of the triplet excited state of 15 from direct irradiation. In contrast. Hurley and Testa used energy transfer to estimate that the triplet excited state of 15 is formed in 67% yield,whereas Takezaki et al. have measured the yields for forming the triplet excited state of 15 to be slightly higher or above 80%. They estimated the lifetime of the lowest triplet excited state of 15 to be 350 ps in ethanol. 

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