Question

Why is the anthracene fluorescence quenching rate diffusion controlled as opposed to chemically controlled? Justify why the reaction between AN* and CBr₄ is very fast.

Answer 1

For diffusion limited quenching, time for quenching particles to diffuse toward and collide with excited particels to diffuse towards and collide with excited particles is the limiting factor.if anyhracene floresence quenching rate is chemically it shud obey volmers equation. The limiting factor should be only the concentration of quenchee.but that is not the case.rate depends on viscosity of solution and diffusion rates too. There for it is a diffusion controlled process.

2. Floresence intensityof a substance depends on natural life time of it's excited single state,rate constant of which first excited state is deactivated by non radioactive processes.some substances are efficient at deactivating or quenching excited states.these are usually substances with heavy atoms. ( halogens ). Floresence of most compounds are efficiently quenched by halogenated alkenes such as ccl4 and cbr4. So rraction is very fast in case 2