Quantum yield triplet

When C60 is irradiated with visible light, it is excited from the S0 ground state to a short-lived (-1.3 ns) S,-excited state (Es 46.1 keal/mol). The St state rapidly decays at a rate of 5.0 x 108 s and a triplet quantum yield (0T) of 1.0 to a lower lying triplet state Tj (/. ., . 37.5kcal/mol) with a long hfetime of 50-lOOps. The Sj—>Tt decay is... 

Triplet quantum yields for eosin and some other dyes have been determinded by Soep et al. The system to be studied is exposed to a dye laser pulse (with tunable wavelength) and the transient absorb-tion changes in the system due to triplet population are recorded with the light from a dc xenon lamp. 

Logarithmic plots of the fluorescence decays for the lowest excited singlet state of H2TPP, H2OEP, and their deuterium analogues were described by single exponential forms. Fluorescence lifetimes of all compounds were obtained by deconvolution and fluorescence quantum yields were determined relative to rhodamine 640 in ethanol (32). Triplet quantum yields (0r) were determined relative to benzophenone in benzene by using the transient absorption (33). Quantum yields and lifetimes determined are summarized in "Table II". 

Fluorescence Lifetimes (T ), Fluorescence Quantum Yields (0f), Triplet Quantum Yields (0 ), and Quantum Yields of Internal Conversion... 

The triplet quantum yield tplsc is for the helicenes nearly (1 — radiationless decay approximates klsc. The low value of kfl shows that the fluorescence of all the compounds occurs from the Lb state. The fluorescence rate (kfj of the helicenes with an odd number of benzene rings decreases more slowly than of the helicenes with an even number of rings. This is explained by the difference in molecular rigidity of the two groups. The even ring helicenes are symmetric about a naph-... 

This biradical-like concerted mechanism, in which the kinetic features reflect the biradical character and the formation of excited-state products can best be rationalized by the concerted nature of the complex reaction coordinate, was proposed to optimally reconcile the experimentally determined activation and excitation parameters of most 1,2-dioxetanes studied and has been called the merged mechanism51-87. Specifically, both thermal stability and singlet and triplet quantum yields in the series of methyl-substituted 1,2-dioxetanes, including the parent 1,2-dioxetane11 50 51, could be readily rationalized on the basis of the merged mechanism and qualitative quantum mechanics considerations86. 

Total quantum yields in the absence of quencher for 2-pentanone and 2-hexanone are 0.20 and 0.25, respectively.326 Subtraction of the quantum yields for singlet reaction from the total quantum yields furnishes values of triplet quantum yields. Stern-Volmer plots of reciprocals of the triplet quantum yields versus piperylene concentration indicate that triplet 2-hexanone is five times as reactive as triplet 2-pentanone.273 Rough measurements have been made with methoxyacetone which suggest that at least 60% of its total photoelimination occurs from an unquenchable singlet state.273... 

Two-substituted naphthalene thienyl oligomers have been characterized for their photophysical properties (09PCCP8706). The compound 7 showed absorption at 405 nm and an emission at 475 and 502 nm. The fluorescence quantum yield was 0.27 and tf 0.56 ns. The quantum yield for the internal conversion was 0.05, while the triplet quantum yield resulted to be 0.68. 

Triplet-triplet absorption maximum Xmax/nrn Extinction coefficient s-T/mol-1 cm-1 Triplet-lifetime T/p,S Triplet quantum yield T t... 

The fullerene triplet quantum yields in 8 72 were determined by the quantitative conversion of the triplet excited states of the porphyrin (0.78) and fullerene (i.e. 0.98) fragments into singlet oxygen. By analyzing the singlet oxygen emission at 1275 nm (see Fig. 8.22), we derived a quantum yield of 0.84. 

Triplet quantum yields (high rate of intersystem crossing (much faster than for typical aromatic hydrocarbons) and the inefficient fluorescence. These values were determined by photothermal and spectroscopic methods and agree with lower limits determined from singlet oxygen quantum yields [9,10]. (see below). A cyclodextrin complex also produces the triplet state efficiently in water [39]. 

The heavy-atom effect of substituents introduced in a porphyrin will depend on the substitution pattern and may be different for Si Ti and Ti So transitions. Thus, it should be possible to control the electronic factor to increase the triplet quantum yield without compromising its lifetime. This hypothesis was investigated in detail using various meso- and beta-substituted free-base and Mg, Zn, or Cd metalloporphyrins (53). It was considered that the spin-orbit coupling of atoms in identical substitution patterns gives additive contributions to the nonadiabatic factor... 

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