Luminescence Spectrometry Molecular Luminescence Spectrometry Chap 15

Factors Affecting Fluorescence and Phosphorescence Quantum Yield Expressed in terms of rate constants: where knr = kvib + kic + kec +kisc + kpd + kd varies from 0 to 1

Factors Affecting Fluorescence and Phosphorescence Transition Types in Fluorescence σ* → σ Transitions (seldom observed) π* → π Transitions (most common, higher ) π*→ n (longer lifetime, lower ) Fluorescence typically from lowest vib. level, vʹ = 0, of excited electronic state

Factors Affecting Fluorescence and Phosphorescence Fluorescence and Structure Most intense from aromatic π* → π transitions increases with: number of fused rings rigidity of structure (lowers kic) Fluorescence and Temperature, Solvent, & pH All must be monitored to minimize kec

Excitation and Emission Spectra of Phenanthrene Fig. 15-5

Components of a Fluorometer or Spectrofluorometer Fig. 15-8 λ λ

Filter Fluorometer Fig. 15-10 Less expensive, rugged, good for concentration measurements

Components of a Spectrofluorometer Fig. 15-11 ∼300 W at 300-1100nm

Fig. 15-11 Resulting emission is isotropic If source is at fixed λ and monochromator is scanned an emission spectrum results. If source is scanned, and monochromator is at a fixed λ, an excitation spectrum results.

Fluorescence Spectra for 1 ppm anthracence in alcohol Fig. 15-9 Fluorescence Spectra for 1 ppm anthracence in alcohol Emission Spectrum: Constant λex Variable Info on vib levels in S1 λem Excitation Spectrum Constant λem Variable λex Info on vib levels in S0