Steric Shielding Effects in Quenching

For this reason, one might expect the quenching efficiency to increase in more viscous solvents, which slow dissociation of the fluorophore and quencher. The increased dun-lion of each diffesive encounter increases the probability of quenching during this encounter. 

For most fluon ore-quencher pairs, quenching is highly efficient, and the quenching efficiency is not known to depend on solvent or viscosity. However, there is a known example where the efficiency is less than unity and dependent on environment, namely, the quenching of indole by succinimide. In this case the quendiing efficiency is near 0.S in protic solvents and decreases to less than 0.05 in pure dioxane. The reason for the changes in efftciency k not known. Such changes could compromise 

Hgure 9JZ4. Model fordieiutenclioiiofftaufocnlyieectlveqaeaefaer (Q) with a pcot that is medvB in a foffcoe uet deicribed by cone an  

---