Luminescence Spectroscopy (Chapter 15) fluorescence ...

How likely is fluorescence?Fluorescence Quantum Yield - ratio of number of moleculesfluorescing to number excitedΦ fluor =# photons fluor# species excited(Φ fluor = 0.0 to 1.0)=k fluork fluor + k int con + k ext con + k ISC + k pre dis + k disWhat Factors Affectfluor?(1) Excitation λShort λ's break bonds increase k pre-dis and k disrarely observedmost commonσ* → σ π* → n π* → πemission usually from lowest lying excited state(2) Lifetime of stateTransition probability measured by εLarge ε implies short lifetimeLargest fluorescence from short lifetime/high ε stateπ*→π > π*→n (10-9-10-7 s > 10-7-10-5 s)CEM 333 page 5.8