12-06-2014, 02:16 PM
Molecular Luminescence
[attachment=64699]
Vibrational Relaxation
Excited molecule rapidly transfers excess vibrational energy to the solvent / medium through collisions.
Molecule quickly relaxes into the ground vibrational level in the excited electronic level.
Non-radiative process
10-11 – 10-10 sec.
External Conversion
Non-radiative transition between electronic states involving transfer of energy to other species (solvent, solutes).
Also referred to as quenching.
Modifying conditions to reduce collisions reduces the rate of external conversion.
Occurs on a comparable time scale as fluorescence.
Are you getting the concept?
For a given fluorophore under steady state conditions, excitation of a 1 cm3 sample volume yields the following first-order rate constants: kf = 5 x 107 s-1, knr = 9 x 105 s-1, and ka = 1 x 1014 s-1 and an overall rate of fluorescence photon emission of 9.8 x 1019 photons/second. What is the molecule number density in the ground electronic state?
Quenching
Static Quenching
Lumophore in ground state and quencher form dark complex. Luminescence is only observed from unbound lumophore. Luminescence lifetime not affected by static quenching.
Dynamic Quenching/Collisional Quenching
Requires contact between quencher and excited lumophore during collision (temperature and viscosity dependent). Luminescence lifetime drops with increasing quencher concentration.
Long-Range Quenching/Förster Quenching
Result of dipole-dipole coupling between donor (lumophore) and acceptor (quencher). Rate of energy transfer drops with R-6. Used to assess distances in proteins.
[attachment=64699]
Vibrational Relaxation
Excited molecule rapidly transfers excess vibrational energy to the solvent / medium through collisions.
Molecule quickly relaxes into the ground vibrational level in the excited electronic level.
Non-radiative process
10-11 – 10-10 sec.
External Conversion
Non-radiative transition between electronic states involving transfer of energy to other species (solvent, solutes).
Also referred to as quenching.
Modifying conditions to reduce collisions reduces the rate of external conversion.
Occurs on a comparable time scale as fluorescence.
Are you getting the concept?
For a given fluorophore under steady state conditions, excitation of a 1 cm3 sample volume yields the following first-order rate constants: kf = 5 x 107 s-1, knr = 9 x 105 s-1, and ka = 1 x 1014 s-1 and an overall rate of fluorescence photon emission of 9.8 x 1019 photons/second. What is the molecule number density in the ground electronic state?
Quenching
Static Quenching
Lumophore in ground state and quencher form dark complex. Luminescence is only observed from unbound lumophore. Luminescence lifetime not affected by static quenching.
Dynamic Quenching/Collisional Quenching
Requires contact between quencher and excited lumophore during collision (temperature and viscosity dependent). Luminescence lifetime drops with increasing quencher concentration.
Long-Range Quenching/Förster Quenching
Result of dipole-dipole coupling between donor (lumophore) and acceptor (quencher). Rate of energy transfer drops with R-6. Used to assess distances in proteins.