Phosphorescence substitution effects

Fig. 23 Entropy effects on intramolecular reactions of polymethylene chains. Plot of 9AS (e.u.) against number of single bonds for (O) nucleophilic substitutions at saturated carbon ( ) electron-exchange reactions (A) quenching of benzophenone phosphorescence. The straight line has intercept +30 e.u. and slope —4.0 e.u. per rotor. The right-hand ordinate reports the purely entropic EM s calculated as exp(0AS /J )...

Substituents have considerable influence on emission characteristics of aromatic compounds. Heavy atom substituents tend to reduce the fluorescence quantum yield 4>f in favour of phosphorescence emission f. In halogen series the effect increases in the order F < Cl < Br < I. In Table 5.1 are recorded experimental data for halogen substituted Naphthalenes. 

Ring substitution can have a very different effect on the phosphorescent properties depending on its size, polarity and ring position. Oxygen quenching studies are consistent with the presence of at least two types of inclusion sites. 

Benzo-fused pyridinium systems also undergo the reaction and a new example, the photocyclisation of (153) to (154) in the presence of iodine, has been published. The quantum efficiency of photocyclisation of l,2-jbis-(a-naphthyl)ethylene to dihydropicene has been examined in micelles and the cyclisation of [5]-helicene (155) to dihydrobenzperylene (156) has been carried out at 4K (156) was characterised by its fluorescence and phosphorescence emission. The effect of different substituents on the photocyclisation of the symmetrically tetra-substituted stilbene (157) has been probed. 

The effect of heavy atoms on the relative yields of fluorescence and phosphorescence has been investigated both by inserting Br and I substituents in the ring of deuterioporphyrin IX and its Zn derivative,340 and by adding ethyl iodide to the solution of a number of free base porphyrins.341 Other authors discuss the luminescence of protoporphyrin IX dimethylester after pulse radiolysis in benzene,848 and from monomeric and dimeric ethylenediamine-substituted protoporphyrin IX and some metal derivatives.343 Several reports consider the emission from porphyrins in Shpolskii matrices and other crystalline organic hosts.344-340... 

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