Quenching singlet

Stephenson monitored the quenching of aromatic hydrocarbon singlet states by observing a decrease in the sensitizer fluorescence intensity with added diene.158 A marked effect of the structure of both the sensitizer and the quencher was noted, with values of kq ranging from 4 x 109 to 8.7 x 10s however, no quantitative correlation between k and several factors that might influence the stability of the proposed excited complex could be obtained (see below). The important observation that singlet quenching led to... 

The above ideas fit in nicely with the work of Cohen and Guttenplan223 who reported the photoreduction of fluorenone by triethylamine. Dilution of neat triethylamine with cyclohexane increased the quantum yield of reduction by decreasing the amount of singlet quenching.221... 

I he triplet quenching constants are one-ninth of the singlet quenching... 

Diphenyliodonium, at a concentration of 0.05 M, does not quench the Eosin triplet. It decreases the fluorescence intensity by a factor of 20 and shifts the fluorescence wavelength 10 nm toward the red. The calculated rate constant for singlet quenching is 5 times larger than for a diffusion controlled... 

VII. REACTIONS OF SINGLET ARENES WITH STILBENES A. Singlet Quenching and Exciplex Formation... 

The initial distribution for short pulse (p = 0) was first derived in Ref. 263, but then generalized for arbitrary p in Refs. 262 and 265. All distributions differ from n(r, 0) = 1 in that the broad near-contact gap is present in each of them. At long times it is burned by only singlet-triplet quenching because the singlet-singlet quenching is already over. 

Fig. 9. The quantum yield for disappearance of BC as a function of [BC]. The lines represent the best fit to the following equation , and

Singlet Quenching by Energy Transfer and Exciplex Formation.—In a series of papers Shetlar has examined the kinetic consequences of there being more than one quenching process in a system. The non-linear Stern-Volmer type expressions derived will be useful in both luminescence studies and studies of photochemical reactions.108... 

The singlet quenching of 10-methylacridinium chloride by chromium(m) complexes is probably an energy-transfer process,149 and a linear free-energy relationship between -values and the rate constants for fluorescence quenching of substituted anthracenes by triphenylphosphine has been recognized.160... 

---