Chromophores quencher pairs

In this chapter results of the picosecond laser photolysis and transient spectral studies on the photoinduced electron transfer between tryptophan or tyrosine and flavins and the relaxation of the produced ion pair state in some flavoproteins are discussed. Moreover, the dynamics of quenching of tryptophan fluorescence in proteins is discussed on the basis of the equations derived by the present authors talcing into account the internal rotation of excited tryptophan which is undergoing the charge transfer interaction with a nearby quencher or energy transfer to an acceptor in proteins. The results of such studies could also help to understand primary processes of the biological photosynthetic reactions and photoreceptors, since both the photoinduced electron transfer and energy transfer phenomena between chromophores of proteins play essential roles in these systems. 

Scheme m illustrates the concept in which complexation of a cation by the crown stiffens the crown ring and enforces a separation of the quencher and c omophore. Complexation may also help to tie up electron pairs that may act as electron-donor-acceptor quenchers. Two early examples in the literature were reported by Konopelski et al. (6) and de Silva et al. (if), and many cases of enhanced fluorescence are likely to have this concept as a basis. We synthesized crown ether 2, a simple molecule that we hoped would illustrate some of the principles of Scheme III (22). Crown 2 has a naphthalene fluorescent chromophore and an aniline electron donor quencher. 

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