Biacetyl phosphorescence

The biacetyl phosphorescence intensity I is given by the following equation ... 

The first quantitative photochemical study of a Rh111 amine was reported by Moggi,8 who noted that both 254 nm (LMCT) and 365 nm (ligand field) excitation of [Rh(NH3)5Cl]2+ caused chloride labilization (equation 131). Other early reports include Basolo s study of the photoinduced stereo-retentive halide aquation from [M(en)2X2]+ (M = Rh, Ir X = Cl, Br, I), and Broomhead s observation of chloride aquation from [RhCl2(phen)2]+.726 While halide labilization dominates upon photolysis of [Rh(NH3)5Cl]2+, both bromo and ammine loss occur upon photolysis of the bromo analog (equation 132)685,707 and ammine is labilized from the iodo analog (equation 133).70 Biacetyl sensitization of the bromo complex quenches the biacetyl phosphorescence, but not the fluorescence,707 consistent with a photoreactive triplet state. 

The increase in the yield of the induced biacetyl phosphorescence with increasing aldehyde pressure is probably due to the competition between... 

Sensitized biacetyl phosphorescence and sensitized decomposition occur in the vapour phase as a result of electronic energy transfer from benzene to biacetyl. Some fluorescence was also observed however, the ratio of phosphorescence to fluorescence was very high. In fluid solutions benzene and some other organic compounds sensitize the biacetyl fluorescence but not the phosphorescence (refs. 316-318), in contrast to the findings for the vapour phase. A satisfactory explanation for this difference is not available at present. 

By competitive methods Ishikawa and Noyes (226) (sensitized biacetyl phosphorescence) and Cundall and Davies (159) (butene-2 isomerization) both estimated the triplet lifetime to be of the order of 10 ys. In a reexamination of the butene-2 system, Lee (227) estimated a value of 100 ys, a finding confirmed by Cundall and Dunnicliff (105). An examination of the kinetics of the benzene photosensitized composition of cyclopentanone decomposition allowed a value of longer than 3 ys to be deduced. This type of experiment is far from satisfactory since photochemical processes can Intervene at low pressures, and impurities and the quenching effects of photoproducts can affect the results. These problems can only be overcome by some form of direct measurement. Parmenter and Ring (228) used a flash method in which 20 torrs of benzene and 0.01 torr of biacetyl were submitted to a 20 J,... 

Under benzophenone-sensitization the quantum yields and the photostationary state are practically independent of the stilbene concentration [25,196], Similar results were obtained with azastilbene sensitized by biacetyl [132] or anthraquinone [206] except for rather low concentrations [120,128], Energy transfer from biacetyl to StPs has also been studied by monitoring the biacetyl phosphorescence [221], With azastilbenes systematic studies have been made concerning the influence of structure on the sensitized isomerization [128, 130, 132, 206]. The results are, however, not easily understood. Relatively low d> -, values were found, the sums of d> c and d>sc, are considerably less than unity and ([e]/[t])scns does not equal Wi-c/Vc. ... 

Figure 14. Absorption spectrum (top) and fluorescence excitation spectrum (middle) of isoquinoline vapor at room temperature, and the excitation spectrum of biacetyl phosphorescence (bottom), sensitized by energy transfer from the triplet isoquinoline. The band positions (in cmT1) are relative to the starred 0+ band at 31,925cm-1. (From ref. [45] with permission.)...

The room-temperature biacetyl phosphorescence sensitized by PNA was much more intense in the presence of P-CD [202]. This was attributed to the organization of the donor-acceptor pair in a smaller reaction volume, which facilitates the triplet-triplet energy transfer. The dimensions of the CD cavity set restrictions on the number of triplet energy donors for which the enhancement was observed. The large cavity of the y-CD is, in general, the best medium to observe this phenomenon [203],... 

In author s group, Gao et al. [65] used PAHs to sensitize biacetyl phosphorescence emission in CD medium and obtained quite good analytical properties as listed in Table 6. 

The claim [12] that the spectrum of 2-butanone chemiluminescence is identical with that of product (biacetyl) phosphorescence, has been confirmed [10]. 

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