Intersystem crossing and internal conversion from the lowest excited singlet state of diazanaphthalenes

1982 ◽  
Vol 86 (11) ◽  
pp. 1976-1979 ◽  
Author(s):  
David W. Boldridge ◽  
Gary W. Scott ◽  
Thomas A. Spiglanin
Keyword(s):  
Internal Conversion ◽  
Singlet State ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet

Photolysis of ketene. I

1968 ◽  
Vol 46 (14) ◽  
pp. 2353-2360 ◽  
Author(s):  
A. N. Strachan ◽  
D. E. Thornton
Keyword(s):  
Carbon Monoxide ◽  
Quantum Yield ◽  
Triplet State ◽  
Singlet State ◽  
Inert Gases ◽  
Inert Gas ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Increasing Temperature

Ketene has been photolyzed at 3660 and 3130 Å both alone and in the presence of the inert gases C4F8 and SF6. The quantum yield of carbon monoxide has been determined at both wavelengths as a function of pressure and temperature. At 3660 Å the quantum yield decreases with increasing pressure but increases with increasing temperature. At 3130 Å the quantum yield with ketene alone remains 2.0 at both 37 and 100 °C at pressures up to 250 mm. At higher pressures of ketene or with added inert gas the quantum yield decreases with increasing pressure. The results are interpreted in terms of a mechanism in which intersystem crossing from the excited singlet state to the triplet state occurs at both wavelengths, and collisional deactivation of the excited singlet state by ketene is single stage at 3660 Å but multistage at 3130 Å.

Fluorescence of chloropentafluoroacetone

1970 ◽  
Vol 48 (16) ◽  
pp. 2611-2616 ◽  
Author(s):  
H. S. Samant ◽  
A. J. Yarwood
Keyword(s):  
Rate Constant ◽  
High Pressures ◽  
Singlet State ◽  
Radiative Lifetime ◽  
Heavy Atom ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Gaseous State ◽  
Fluorescent State

The fluorescence of chloropentafluoroacetone in the gaseous state at room temperature is reported. The fluorescence extends from 337 nm to greater than 560 nm with a maximum intensity at 420 nm and is unaffected by low pressures of oxygen. The energy of the first excited singlet state is estimated as about 83 kcal and the fluorescence data for 313 and "290" nm excitation indicate that fluorescence enhancement occurs as the pressure increases. The fluorescent yield at high pressures [Formula: see text] is independent of the nature of the gas used to attain the high pressure. The lifetime of the fluorescent state is 35.1 ± 0.3 ns.A simple mechanism correlates the experimental observations and the values of the rate constants are considered. The reciprocal of the natural radiative lifetime is calculated to be 6.6 × 105 s−1 and the rate constant assigned to intersystem crossing to the triplet is 2.8 × 107 s−1. A comparison with the data in the literature for hexafluoroacetone shows the effect of substitution by a heavy atom in the fluorinated ketone. It about doubles the value of the rate constant associated with intersystem crossing from the first excited singlet state in the gas phase.

The primary process in the photolysis of hexafluoroacetone vapour III. The efficiency of intersystem crossing

1968 ◽  
Vol 306 (1487) ◽  
pp. 529-536 ◽  
Keyword(s):  
Quantum Yield ◽  
Lower Limit ◽  
Singlet State ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Primary Process ◽  
Excited Singlet ◽  
A Value ◽  
Low Concentrations

The value of k 6 /( k 4 + k 5 + k 6 ) (mechanism of part I) was determined by two techniques, namely the sensitization of the isomerization of cis - to trans -butene-2 and the sensitization of the phosphorescence of biacetyl. Both techniques yielded a value for the ratio of 0⋅9 ± 0⋅1. The value obtained by the isomerization technique is a lower limit because the quantum yield for the isomerization did not attain a value independent of [ cis -butene-2], but reached a maximum at low concentrations of olefine and then decreased. A similar scavenging of the excited singlet state of hexafluoroacetone was observed when biacetyl was present as an addend. However, in both cases the measurements were made with sufficiently low concentrations of addend that the singlet scavenging should have introduced less, than 10% error. It is concluded that reaction (5) of the mechanism cannot be an important mode of disappearance of excited ketone molecules.

The radiation-induced formation of excited states of aromatic hydrocarbons in benzene and cyclohexane. III. Effect of singlet state quenchers

1972 ◽  
Vol 328 (1575) ◽  
pp. 481-496 ◽  
Keyword(s):  
Triplet State ◽  
Excited States ◽  
State Formation ◽  
Aromatic Hydrocarbons ◽  
Extinction Coefficient ◽  
Singlet State ◽  
Excited Singlet State ◽  
Intersystem Crossing ◽  
Excited Singlet ◽  
Radiation Induced

The contribution to naphthalene and pyrene triplet state formation of intersystem crossing from the excited singlet state has been determined for both cyclohexane and benzene solutions using the singlet state quenchers nitromethane and xenon. In agreement with the conclusions reported in part II, intersystem crossing plays an important role; under certain conditions up to 50 % of the total triplet yield in naphthalene-cyclohexane solutions has this origin. The extinction coefficient for naphthalene triplet absorption in cyclohexane at λ max = 412.5 nm is 20 000 ± 5000 1 mol -1 cm -1 .

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