Naphthalene intersystem crossing

S - S absorption and intersystem crossings from the state of naphthalene in cyclohexane at room temperature were studied by Bonneau et al i using a neodymium laser ( X = 1.0 /x,... 

An alternate method can be used to obtain separate from the intersystem crossing quantum yield. In this case, we will also use benzophenone (BP) and naphthalene (N) as our example. Now one of our samples will contain both compounds, and we will choose the concentration of naphthalene so that it will quench at least 98% of the benzophenone triplets. This will require knowledge of the... 

Evidence for photoassociation in the triplet manifold is at present inconclusive. Although Hoytink et al.20 have reported excimer phosphorescence from cooled ethanolic solutions of phenanthrene and naphthalene, concentration and temperature-dependent studies of the emission characteristics must be extended in order to distinguish photoassociation of the triplet state from intersystem crossing of the singlet excimer and possible triple-triplet annihilation. Certainly the decay constant of the molecular triplet state in fluid media is relatively insensitive to solute concentration21 although this... 

Spectroscopic evidence has also been adduced for the ability of the anthracene T2 to transfer energy to other substances.239 Selective excitation of guest anthracene in a host dibenzofuran crystal also containing napthalene-d8 as a guest resulted in naphthalene phosphorescence. As shown in Figure 8, the path of the energy is S0 -> Sj excitation of anthracene, intersystem crossing... 

Wilkinson has recently described a novel approach.113 It has long been known that solvents containing heavy atoms markedly quench the fluorescence of aromatic hydrocarbons, and it has been shown that this effect arises from an enhancement of the rate of intersystem crossing. Thus the ratio of phosphorescence to fluorescence for naphthalene irradiated at 77°K can be increased more than a hundredfold upon addition of some isopropyl iodide to the solvent.114 The same effect has been noted upon changing from hydrocarbon glasses to frozen krypton and xenon matrices.115 Wilkinson found that the decrease in fluorescence intensity from irradiated solutions of anthracene and some of its derivatives upon addition of bromobenzene is attended by an increase in T-T absorption intensity.116 The fluorescence quenching follows the Stern-Volmer law ... 

Quantum yields for isomerization of t-1 to c-1 via intersystem crossing are similar to those obtained in triplet sensitization, indicating that t is formed with near unit efficiency. Similar results were reported for the interaction of t with inorganic anion electron donors (127b). Rate constants for intersystem crossing of the t-1-ethyldiisopropylamine and triethylamine exciplexes obtained from the measured exciplex lifetimes are 5 x 107 s"1 (116), similar to the values for the exciplexes of pyrene (128) and naphthalene (121) with triethylamine. Larger intersystem crossing rate constants are observed for the exciplexes of t-1 with the bicyclic amines l-azabicyclo[2.2.2]-... 

Table I shows that in either dioxane or acetonitrile the quantum yield for degradation of I, is unaffected by the presence of 0.1 M of triplet quencher, either sorbic acid, naphthalene or cyclohexadiene. In ethanol, triplet quenchers reduce < >d from 0.34 to 0.14. Quantum yields for intersystem crossing, as determined by a laser opto-acoustic technique ( ), were 0.36 in ethanol and 0.59 in dioxane. These results agree with our earlier report (3), and indicate that significant reactivity occurs from St of I in protic solvents, and that reaction occurs exclusively from Sx in aprotic solvents. While triplet quenching experiments cannot rigorously exclude participation by short-lived higher triplet states, Palm et al (9) have obtained conclusive evidence from CIDNP experiments for singlet-state participation in a series of aryloxy-acetophenones. Note that the triplet state of I is formed in aprotic solvents, and that in deaerated solutions at room temperature it decays by first-order kinetics with a lifetime of 200 ns (3). Remarkably, despite having lifetimes about 100 times longer than other, differently-substituted, aryloxyacetophenones (the longer lifetimes may...

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