Acenaphthene. fluorescence quenching

The steroidal ketone 51 quenches acenaphthene fluorescence at a diffusion controlled rate211 and the rearrangement shown214 is sensitized by acenaph-... 

In a careful study of cyclopentenone photocycloaddition reaction, DeMayo and coworkers215 have noted that ketone sensitizers of triplet energy less than 71.2 kcal did not sensitize cycloaddition to cyclohexene. Triphenylene (Et = 66.6 kcal) and acenaphthene (ET = 59.3 kcal) were exceptional since they resulted in quantum yields of 0.10 and 0.21, respectively. This behavior, as well as the fact that 0.1 M cyclopentenone quenched acenaphthene fluorescence by 90% in an EPA (ether-isopentane-alcohol) glass at 77°K strongly implicate singlet energy transfer. 

Naphthalene, 1-methyl-naphthalene, and acenaphthene fluorescence in water is quenched by trimethylamine (TMA) without the formation of an... 

ABSTRACT. The fluorescence quenching of naphthalene, 1-methylnaph-thalene, and acenaphthene by trimethylamine (TMA) was studied in aqueous 3-cyclodextrin (3-CD) solutions to know the structural requirements for guest molecules to form three-component complexes. The apparent rates for the fluorescence quenching of the naphthalene derivatives by TMA markedly increased in the presence of3-CD. The fluorescence quenching of 1-methylnaphthalene and acenaphthene by TMA was accelerated by 3-CD more efficently than that of naphthalene. These results suggest the structures of the three-component complexes as the arene-capped 3-CD including TMA in its cavity. 

The fluorescence quenching can be regarded as a probe reaction for investigating the effects of CD on bimolecular reactions. Especially, the structural requirements for guest molecules to form three-component complex can be studied by this method. Formation of three-component complexes is essentially important to realize CD-catalyzed bimolecular reactions. In the present work, we studied the fluorescence quenching of naphthalene, 1-methylnaphthalene, and acenaphthene by TMA in aqueous 3-CD solutions to clarify the steric factors affecting the formation of the three-component complexes. 

A. Meanwhile, 1-methylnaphthalene has a size of 8.5 A x 7.6 A and may bind shallowly to 3-CD. Acenaphthene will bind more shallowly than 1-methylnaphthalene. We studied how the difference in the structures between these naphthalene derivatives affects the fluorescence quenching of these fluorescers by TMA in 3-CD solutions. 

This phenomenon appears to be quite general since triethylamine quenches acenaphthene singlets in acetonitrile at the rate of 2 x 109 M-1 sec-1 as determined by intensity and lifetime measurements. Quenching of triphenylene fluorescence also occurs at this rate in acetonitrile but is two orders of magnitude slower in isooctane. P. S. Engel, Unpublished results. 

The K values suggest that over 50% of the naphthalene derivative molecules does not bind to 3-CD under the conditions of [naphthalene derivative] = 1 x 10" M and [B-CD] = 1 x 10 M, the ratios of the free molecules being 58% for naphthalene, 6. % for 1-methylnaphthalene, and 79% for acenaphthene. The K value of TMA with 3-CD has been determined as 51 M at 25 C (3b), suggesting that the concentration of the TMA-3-CD complex is 3 3 x 10 M when TMA was added into the 1 x 10 M 3-CD solution to adjust [TMA] = 1 x 10 M. If the fluorescer molecules distribute between the 3-CD cavities and the aqueous bulk phase, it is expected that the plot of Iq/I vs. [TMA] for each system levels off. The plot of Iq/I vs. [TMA], however, was linear till over 80% of the added fluorescer molecules was quenched. This novel phenomenon may be interpreted as that the TMA-3-CD complex tends to bind strongly with naphthalene derivatives. Further studies need to clarify this point. 

---